CK
C. Kasbergen
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1
Micromechanical Modelling of Asphalt Concrete Mixtures with RAP-Modified Binders
Upscaling Sustainable Pavement Materials
Asphalt mixtures are multiscale composites composed of bituminous binder and aggregates of varying sizes. While testing is possible at each level, mixture-scale testing remains standard due to its direct relevance for pavement design. However, mixture-scale testing is time-consuming and resource-intensive. With growing use of sustainable practices, such as higher reclaimed asphalt pavement (RAP) content, lower production temperatures and alternative binders, uncertainty in mixture performance increases. This research investigates the potential of micromechanical models to upscale mechanical properties from mortar to mixture level in five AC16 mix designs that reflect current sustainability practices. These include mix designs with 60% RAP, a warm mix additive, a bio-based binder, and natural bitumen. Specimens were prepared from each mix design and tested using a dynamic shear rheometer (DSR) for mortars and a cyclic indirect tension (CIT-CY) device for mixtures. Nine Eshelby-based micromechanical models were evaluated for predicting the mixture properties. Among the evaluated models, the generalized self-consistent (GSC) model showed the most consistent performance, with prediction errors for mixture stiffness remaining below 10% at intermediate and high loading frequencies. However, none of the models were able to accurately capture the mixture stiffness observed at low frequencies (below 0.1 Hz), which is mainly attributed to particle-contact reinforcement. To address this limitation, a linear regression function was introduced. When combined with the GSC model, this hybrid approach successfully predicted the mixture stiffness across a wide frequency range in all five AC16 mix designs. Furthermore, fatigue behaviour was predicted by upscaling stiffness–load cycles (S-N) curves from mortar to mixture level. Three upscaling approaches were assessed to predict mixture fatigue behaviour: (i) direct upscaling from linear amplitude sweep (LAS) tests, (ii) direct upscaling from time sweep (TS) tests, and (iii) simulation-based upscaling using a Burgers model with a damage component. LAS-based S-N curves proved unsuitable for direct upscaling because the accelerated nature of the test caused rapid damage accumulation, which is reflected in the measured curves. In contrast, TS tests produced more representative S-N curves at the mortar-scale. When combined with a calibrated strain scaling factor, direct upscaling of TS-based S-N curves aligned well with the measured mixture fatigue lives. The simulation-based method showed promise for reproducing measured fatigue behaviour but was ultimately constrained by high computational demands. This study concludes that stiffness in AC16 mixtures with RAP-modified binders can be reliably predicted from the mortar level using micromechanical models. For predicting fatigue behaviour, the study provides a valuable contribution by evaluating LAS-based, TS-based, and simulation-based approaches, advancing the development of fatigue prediction methods for asphalt mixtures.
...
Asphalt mixtures are multiscale composites composed of bituminous binder and aggregates of varying sizes. While testing is possible at each level, mixture-scale testing remains standard due to its direct relevance for pavement design. However, mixture-scale testing is time-consuming and resource-intensive. With growing use of sustainable practices, such as higher reclaimed asphalt pavement (RAP) content, lower production temperatures and alternative binders, uncertainty in mixture performance increases. This research investigates the potential of micromechanical models to upscale mechanical properties from mortar to mixture level in five AC16 mix designs that reflect current sustainability practices. These include mix designs with 60% RAP, a warm mix additive, a bio-based binder, and natural bitumen. Specimens were prepared from each mix design and tested using a dynamic shear rheometer (DSR) for mortars and a cyclic indirect tension (CIT-CY) device for mixtures. Nine Eshelby-based micromechanical models were evaluated for predicting the mixture properties. Among the evaluated models, the generalized self-consistent (GSC) model showed the most consistent performance, with prediction errors for mixture stiffness remaining below 10% at intermediate and high loading frequencies. However, none of the models were able to accurately capture the mixture stiffness observed at low frequencies (below 0.1 Hz), which is mainly attributed to particle-contact reinforcement. To address this limitation, a linear regression function was introduced. When combined with the GSC model, this hybrid approach successfully predicted the mixture stiffness across a wide frequency range in all five AC16 mix designs. Furthermore, fatigue behaviour was predicted by upscaling stiffness–load cycles (S-N) curves from mortar to mixture level. Three upscaling approaches were assessed to predict mixture fatigue behaviour: (i) direct upscaling from linear amplitude sweep (LAS) tests, (ii) direct upscaling from time sweep (TS) tests, and (iii) simulation-based upscaling using a Burgers model with a damage component. LAS-based S-N curves proved unsuitable for direct upscaling because the accelerated nature of the test caused rapid damage accumulation, which is reflected in the measured curves. In contrast, TS tests produced more representative S-N curves at the mortar-scale. When combined with a calibrated strain scaling factor, direct upscaling of TS-based S-N curves aligned well with the measured mixture fatigue lives. The simulation-based method showed promise for reproducing measured fatigue behaviour but was ultimately constrained by high computational demands. This study concludes that stiffness in AC16 mixtures with RAP-modified binders can be reliably predicted from the mortar level using micromechanical models. For predicting fatigue behaviour, the study provides a valuable contribution by evaluating LAS-based, TS-based, and simulation-based approaches, advancing the development of fatigue prediction methods for asphalt mixtures.
Enhanced Jack-Up Vessel Modelling with Superelements for Structural Integrity Analysis
A Study Balancing Computational Time and Accuracy to improve FEM Modelling
The increasing demand for renewable energy sources presents challenges to the offshore wind industry. As wind turbine generators grow in size, their foundations must scale accordingly. The growing monopile weights are posing risks to existing jack-up vessels that install these components. The increasing weight of monopiles results in larger deck loads, which requires engineers to assess the structural integrity of these vessels using the finite element method. However, due to the substantial size of these vessels, finite element models require significant computational resources. Therefore, efficient methods are needed to reduce model size and complexity.
While the literature does not specifically address finite element techniques for jack-up vessels, similar challenges have been extensively studied in the field of aerospace engineering. Such finite element techniques include, surrogate models, adaptive mesh refinement, submodelling, substructuring and model order reduction. The application of these techniques is mainly due to the significant size of the structures they are used to deal with, resulting in a reduction of computational time. A combination of substructuring and model order reduction results in a superelement. Its potential in this engineering discipline is the main reason for its selection in this research.
To understand the behaviour of superelements and their impact on computational time and accuracy, an exploratory study was conducted, comparing the results to a reference model without superelements. Parameters that potentially influence the performance and outcome of the results are studied. These parameters include model complexity (1D versus 2D finite elements), the number of superelements applied to the model, the mesh size of the superelement, the number of modes incorporated in the superelements solution, and the connection type. Based on the outcome of the exploratory study, the parameters are reevaluated and used to validate the applicability to an existing model of a jack-up vessel via a case study.
The case study utilises the outcomes of the exploratory study to a real-world model of a jack-up vessel. Several locations at the structural elements of a jack-up vessel are compared while reducing the size of the model's stiffness matrix with five variations. The first serves as the reference model with no superelements. The second introduces superelements for the legs, the third adds the stern, the fourth incorporates the bow, and the fifth further includes detailed deck geometry to the superelement of the stern already made in the third iteration. As a result, the stiffness matrix decreases up to 42%, reducing the computational time by 47% in the fifth variation. However, the fifth variation shows inaccuracies in total deformation and underestimates the von Mises stress by up to 15%. In contrast, the fourth variation demonstrated a more reliable balance between efficiency and accuracy, with a 21% reduction in the size of the stiffness matrix, a 23% improvement in computational time per single run, and deformation and stress deviations of 3% and 10%, respectively.
A more representative measure for evaluating computational efficiency is the scenario in which an engineer is required to solve a model 50 times due to changes in its geometry. In this case, the superelements computational time is included, but it should be noted that this is only required for the initial run. The cumulative computational time for variation four demonstrates that the application of superelements becomes more efficient than the conventional approach from the sixth run onwards. This results in a 26% increase in efficiency over 50 runs.
This study shows that superelements can effectively reduce model size and computational effort when assessing jack-up vessels' structural integrity. While accuracy deviations must be evaluated carefully, this research presents that superelements can substantially increase the efficiency with minimal loss in accuracy. This suggests that superelements are a promising method to apply for structural integrity analysis on large structures such as jack-up vessels.
...
While the literature does not specifically address finite element techniques for jack-up vessels, similar challenges have been extensively studied in the field of aerospace engineering. Such finite element techniques include, surrogate models, adaptive mesh refinement, submodelling, substructuring and model order reduction. The application of these techniques is mainly due to the significant size of the structures they are used to deal with, resulting in a reduction of computational time. A combination of substructuring and model order reduction results in a superelement. Its potential in this engineering discipline is the main reason for its selection in this research.
To understand the behaviour of superelements and their impact on computational time and accuracy, an exploratory study was conducted, comparing the results to a reference model without superelements. Parameters that potentially influence the performance and outcome of the results are studied. These parameters include model complexity (1D versus 2D finite elements), the number of superelements applied to the model, the mesh size of the superelement, the number of modes incorporated in the superelements solution, and the connection type. Based on the outcome of the exploratory study, the parameters are reevaluated and used to validate the applicability to an existing model of a jack-up vessel via a case study.
The case study utilises the outcomes of the exploratory study to a real-world model of a jack-up vessel. Several locations at the structural elements of a jack-up vessel are compared while reducing the size of the model's stiffness matrix with five variations. The first serves as the reference model with no superelements. The second introduces superelements for the legs, the third adds the stern, the fourth incorporates the bow, and the fifth further includes detailed deck geometry to the superelement of the stern already made in the third iteration. As a result, the stiffness matrix decreases up to 42%, reducing the computational time by 47% in the fifth variation. However, the fifth variation shows inaccuracies in total deformation and underestimates the von Mises stress by up to 15%. In contrast, the fourth variation demonstrated a more reliable balance between efficiency and accuracy, with a 21% reduction in the size of the stiffness matrix, a 23% improvement in computational time per single run, and deformation and stress deviations of 3% and 10%, respectively.
A more representative measure for evaluating computational efficiency is the scenario in which an engineer is required to solve a model 50 times due to changes in its geometry. In this case, the superelements computational time is included, but it should be noted that this is only required for the initial run. The cumulative computational time for variation four demonstrates that the application of superelements becomes more efficient than the conventional approach from the sixth run onwards. This results in a 26% increase in efficiency over 50 runs.
This study shows that superelements can effectively reduce model size and computational effort when assessing jack-up vessels' structural integrity. While accuracy deviations must be evaluated carefully, this research presents that superelements can substantially increase the efficiency with minimal loss in accuracy. This suggests that superelements are a promising method to apply for structural integrity analysis on large structures such as jack-up vessels.
...
The increasing demand for renewable energy sources presents challenges to the offshore wind industry. As wind turbine generators grow in size, their foundations must scale accordingly. The growing monopile weights are posing risks to existing jack-up vessels that install these components. The increasing weight of monopiles results in larger deck loads, which requires engineers to assess the structural integrity of these vessels using the finite element method. However, due to the substantial size of these vessels, finite element models require significant computational resources. Therefore, efficient methods are needed to reduce model size and complexity.
While the literature does not specifically address finite element techniques for jack-up vessels, similar challenges have been extensively studied in the field of aerospace engineering. Such finite element techniques include, surrogate models, adaptive mesh refinement, submodelling, substructuring and model order reduction. The application of these techniques is mainly due to the significant size of the structures they are used to deal with, resulting in a reduction of computational time. A combination of substructuring and model order reduction results in a superelement. Its potential in this engineering discipline is the main reason for its selection in this research.
To understand the behaviour of superelements and their impact on computational time and accuracy, an exploratory study was conducted, comparing the results to a reference model without superelements. Parameters that potentially influence the performance and outcome of the results are studied. These parameters include model complexity (1D versus 2D finite elements), the number of superelements applied to the model, the mesh size of the superelement, the number of modes incorporated in the superelements solution, and the connection type. Based on the outcome of the exploratory study, the parameters are reevaluated and used to validate the applicability to an existing model of a jack-up vessel via a case study.
The case study utilises the outcomes of the exploratory study to a real-world model of a jack-up vessel. Several locations at the structural elements of a jack-up vessel are compared while reducing the size of the model's stiffness matrix with five variations. The first serves as the reference model with no superelements. The second introduces superelements for the legs, the third adds the stern, the fourth incorporates the bow, and the fifth further includes detailed deck geometry to the superelement of the stern already made in the third iteration. As a result, the stiffness matrix decreases up to 42%, reducing the computational time by 47% in the fifth variation. However, the fifth variation shows inaccuracies in total deformation and underestimates the von Mises stress by up to 15%. In contrast, the fourth variation demonstrated a more reliable balance between efficiency and accuracy, with a 21% reduction in the size of the stiffness matrix, a 23% improvement in computational time per single run, and deformation and stress deviations of 3% and 10%, respectively.
A more representative measure for evaluating computational efficiency is the scenario in which an engineer is required to solve a model 50 times due to changes in its geometry. In this case, the superelements computational time is included, but it should be noted that this is only required for the initial run. The cumulative computational time for variation four demonstrates that the application of superelements becomes more efficient than the conventional approach from the sixth run onwards. This results in a 26% increase in efficiency over 50 runs.
This study shows that superelements can effectively reduce model size and computational effort when assessing jack-up vessels' structural integrity. While accuracy deviations must be evaluated carefully, this research presents that superelements can substantially increase the efficiency with minimal loss in accuracy. This suggests that superelements are a promising method to apply for structural integrity analysis on large structures such as jack-up vessels.
While the literature does not specifically address finite element techniques for jack-up vessels, similar challenges have been extensively studied in the field of aerospace engineering. Such finite element techniques include, surrogate models, adaptive mesh refinement, submodelling, substructuring and model order reduction. The application of these techniques is mainly due to the significant size of the structures they are used to deal with, resulting in a reduction of computational time. A combination of substructuring and model order reduction results in a superelement. Its potential in this engineering discipline is the main reason for its selection in this research.
To understand the behaviour of superelements and their impact on computational time and accuracy, an exploratory study was conducted, comparing the results to a reference model without superelements. Parameters that potentially influence the performance and outcome of the results are studied. These parameters include model complexity (1D versus 2D finite elements), the number of superelements applied to the model, the mesh size of the superelement, the number of modes incorporated in the superelements solution, and the connection type. Based on the outcome of the exploratory study, the parameters are reevaluated and used to validate the applicability to an existing model of a jack-up vessel via a case study.
The case study utilises the outcomes of the exploratory study to a real-world model of a jack-up vessel. Several locations at the structural elements of a jack-up vessel are compared while reducing the size of the model's stiffness matrix with five variations. The first serves as the reference model with no superelements. The second introduces superelements for the legs, the third adds the stern, the fourth incorporates the bow, and the fifth further includes detailed deck geometry to the superelement of the stern already made in the third iteration. As a result, the stiffness matrix decreases up to 42%, reducing the computational time by 47% in the fifth variation. However, the fifth variation shows inaccuracies in total deformation and underestimates the von Mises stress by up to 15%. In contrast, the fourth variation demonstrated a more reliable balance between efficiency and accuracy, with a 21% reduction in the size of the stiffness matrix, a 23% improvement in computational time per single run, and deformation and stress deviations of 3% and 10%, respectively.
A more representative measure for evaluating computational efficiency is the scenario in which an engineer is required to solve a model 50 times due to changes in its geometry. In this case, the superelements computational time is included, but it should be noted that this is only required for the initial run. The cumulative computational time for variation four demonstrates that the application of superelements becomes more efficient than the conventional approach from the sixth run onwards. This results in a 26% increase in efficiency over 50 runs.
This study shows that superelements can effectively reduce model size and computational effort when assessing jack-up vessels' structural integrity. While accuracy deviations must be evaluated carefully, this research presents that superelements can substantially increase the efficiency with minimal loss in accuracy. This suggests that superelements are a promising method to apply for structural integrity analysis on large structures such as jack-up vessels.
Vibrational Analysis of Conical Shells
Development of a Semi-Analytical Finite Element Method
This thesis presents the development and validation of a Semi-Analytical Finite Element (SAFE) model for conical shells. The motivation behind this research is to provide a computationally efficient and accurate numerical model for analysing conical shells. Starting with general equations of motion, kinematic equations, constitutive equations, and boundary conditions, the SAFE method is used to construct a numerical framework for conical shells.
Validation of the SAFE method is performed through comparative analyses with a detailed COMSOL model. The comparison focuses on the natural frequencies, mode shapes, and responses to both uniform and non-uniform harmonic loading. The results demonstrate that the SAFE method achieves accurate predictions in all analyses.
To demonstrate the robustness of the SAFE model, the analysis is extended to include a coupled conical-cylindrical shell system. Similar analyses are performed, and the model continues to provide accurate predictions.
These findings highlight the capability of the SAFE method in delivering both computationally efficient and accurate solutions for the analysis of conical shells. ...
Validation of the SAFE method is performed through comparative analyses with a detailed COMSOL model. The comparison focuses on the natural frequencies, mode shapes, and responses to both uniform and non-uniform harmonic loading. The results demonstrate that the SAFE method achieves accurate predictions in all analyses.
To demonstrate the robustness of the SAFE model, the analysis is extended to include a coupled conical-cylindrical shell system. Similar analyses are performed, and the model continues to provide accurate predictions.
These findings highlight the capability of the SAFE method in delivering both computationally efficient and accurate solutions for the analysis of conical shells. ...
This thesis presents the development and validation of a Semi-Analytical Finite Element (SAFE) model for conical shells. The motivation behind this research is to provide a computationally efficient and accurate numerical model for analysing conical shells. Starting with general equations of motion, kinematic equations, constitutive equations, and boundary conditions, the SAFE method is used to construct a numerical framework for conical shells.
Validation of the SAFE method is performed through comparative analyses with a detailed COMSOL model. The comparison focuses on the natural frequencies, mode shapes, and responses to both uniform and non-uniform harmonic loading. The results demonstrate that the SAFE method achieves accurate predictions in all analyses.
To demonstrate the robustness of the SAFE model, the analysis is extended to include a coupled conical-cylindrical shell system. Similar analyses are performed, and the model continues to provide accurate predictions.
These findings highlight the capability of the SAFE method in delivering both computationally efficient and accurate solutions for the analysis of conical shells.
Validation of the SAFE method is performed through comparative analyses with a detailed COMSOL model. The comparison focuses on the natural frequencies, mode shapes, and responses to both uniform and non-uniform harmonic loading. The results demonstrate that the SAFE method achieves accurate predictions in all analyses.
To demonstrate the robustness of the SAFE model, the analysis is extended to include a coupled conical-cylindrical shell system. Similar analyses are performed, and the model continues to provide accurate predictions.
These findings highlight the capability of the SAFE method in delivering both computationally efficient and accurate solutions for the analysis of conical shells.
Master thesis
(2024)
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S.G.M. Gogulapati, K. Anupam, C. Kasbergen, W.A.A.S. Wagasing Arachchige, Z. Yang, Mohan Salil
Sustainability has become a paramount concern in modern research, aligning with global efforts to reduce carbon emissions and embrace circular economy principles. The mentioned imperative extends to the field of pavement engineering, where the widening of existing pavements, a common practice to accommodate increasing traffic demands, necessitates sustainable solutions. The current thesis addresses the pressing need for pavement engineering practices that align with ambitious sustainability goals while ensuring structural integrity and performance.
Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization.
Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models.
The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures.
The main thesis objective is the development of an elasto-visco-plastic (EVP) material model, to capture the time-dependent behaviour exhibited by asphalt surfaces under varying loading conditions. Using the Finite Element Method (FEM), the developed material model serves as a foundational pillar for subsequent investigations, facilitating an examination of stress distribution patterns within widened pavement structures.
The Research provides a detailed framework for conducting the study on pavement widenings. It begins with the delineation of study parameters, including cross-sectional geometry, material properties, and simulation techniques. The development and validation of the EVP material model are elaborated, along with the implementation of finite element method (FEM) simulations to analyse stress distributions. Parametric analyses are conducted to investigate the effects of load variations, base layer characteristics, and interface modelling on widened pavement performance. The methodology also includes the utilization of cohesive zone modelling for interface characterization, enabling a more detailed representation of pavement layer interfaces.
The identification of critical stress concentrations emerges as a focal point of inquiry, necessitating a crucial to understand the interplay between load variations, base layer thickness, and material stiffness. Through various numerical analyses, the study seeks to unravel the intricate web of factors influencing stress propagation within widened pavement structures. Moreover, the implications of reduced recessing length and base layers in new pavement designs are subjected to meticulous scrutiny, shedding light on potential trade-offs between structural integrity and resource optimization.
Overall, the current thesis contributes to advancing pavement engineering practices, promoting sustainable transportation infrastructure, and supporting global sustainability goals. Through rigorous analysis and modelling, the research seeks to enhance the understanding of critical factors influencing widened pavement performance, paving the way for safer, more efficient, and environmentally conscious road networks.
...
Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization.
Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models.
The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures.
The main thesis objective is the development of an elasto-visco-plastic (EVP) material model, to capture the time-dependent behaviour exhibited by asphalt surfaces under varying loading conditions. Using the Finite Element Method (FEM), the developed material model serves as a foundational pillar for subsequent investigations, facilitating an examination of stress distribution patterns within widened pavement structures.
The Research provides a detailed framework for conducting the study on pavement widenings. It begins with the delineation of study parameters, including cross-sectional geometry, material properties, and simulation techniques. The development and validation of the EVP material model are elaborated, along with the implementation of finite element method (FEM) simulations to analyse stress distributions. Parametric analyses are conducted to investigate the effects of load variations, base layer characteristics, and interface modelling on widened pavement performance. The methodology also includes the utilization of cohesive zone modelling for interface characterization, enabling a more detailed representation of pavement layer interfaces.
The identification of critical stress concentrations emerges as a focal point of inquiry, necessitating a crucial to understand the interplay between load variations, base layer thickness, and material stiffness. Through various numerical analyses, the study seeks to unravel the intricate web of factors influencing stress propagation within widened pavement structures. Moreover, the implications of reduced recessing length and base layers in new pavement designs are subjected to meticulous scrutiny, shedding light on potential trade-offs between structural integrity and resource optimization.
Overall, the current thesis contributes to advancing pavement engineering practices, promoting sustainable transportation infrastructure, and supporting global sustainability goals. Through rigorous analysis and modelling, the research seeks to enhance the understanding of critical factors influencing widened pavement performance, paving the way for safer, more efficient, and environmentally conscious road networks.
...
Sustainability has become a paramount concern in modern research, aligning with global efforts to reduce carbon emissions and embrace circular economy principles. The mentioned imperative extends to the field of pavement engineering, where the widening of existing pavements, a common practice to accommodate increasing traffic demands, necessitates sustainable solutions. The current thesis addresses the pressing need for pavement engineering practices that align with ambitious sustainability goals while ensuring structural integrity and performance.
Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization.
Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models.
The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures.
The main thesis objective is the development of an elasto-visco-plastic (EVP) material model, to capture the time-dependent behaviour exhibited by asphalt surfaces under varying loading conditions. Using the Finite Element Method (FEM), the developed material model serves as a foundational pillar for subsequent investigations, facilitating an examination of stress distribution patterns within widened pavement structures.
The Research provides a detailed framework for conducting the study on pavement widenings. It begins with the delineation of study parameters, including cross-sectional geometry, material properties, and simulation techniques. The development and validation of the EVP material model are elaborated, along with the implementation of finite element method (FEM) simulations to analyse stress distributions. Parametric analyses are conducted to investigate the effects of load variations, base layer characteristics, and interface modelling on widened pavement performance. The methodology also includes the utilization of cohesive zone modelling for interface characterization, enabling a more detailed representation of pavement layer interfaces.
The identification of critical stress concentrations emerges as a focal point of inquiry, necessitating a crucial to understand the interplay between load variations, base layer thickness, and material stiffness. Through various numerical analyses, the study seeks to unravel the intricate web of factors influencing stress propagation within widened pavement structures. Moreover, the implications of reduced recessing length and base layers in new pavement designs are subjected to meticulous scrutiny, shedding light on potential trade-offs between structural integrity and resource optimization.
Overall, the current thesis contributes to advancing pavement engineering practices, promoting sustainable transportation infrastructure, and supporting global sustainability goals. Through rigorous analysis and modelling, the research seeks to enhance the understanding of critical factors influencing widened pavement performance, paving the way for safer, more efficient, and environmentally conscious road networks.
Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization.
Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models.
The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures.
The main thesis objective is the development of an elasto-visco-plastic (EVP) material model, to capture the time-dependent behaviour exhibited by asphalt surfaces under varying loading conditions. Using the Finite Element Method (FEM), the developed material model serves as a foundational pillar for subsequent investigations, facilitating an examination of stress distribution patterns within widened pavement structures.
The Research provides a detailed framework for conducting the study on pavement widenings. It begins with the delineation of study parameters, including cross-sectional geometry, material properties, and simulation techniques. The development and validation of the EVP material model are elaborated, along with the implementation of finite element method (FEM) simulations to analyse stress distributions. Parametric analyses are conducted to investigate the effects of load variations, base layer characteristics, and interface modelling on widened pavement performance. The methodology also includes the utilization of cohesive zone modelling for interface characterization, enabling a more detailed representation of pavement layer interfaces.
The identification of critical stress concentrations emerges as a focal point of inquiry, necessitating a crucial to understand the interplay between load variations, base layer thickness, and material stiffness. Through various numerical analyses, the study seeks to unravel the intricate web of factors influencing stress propagation within widened pavement structures. Moreover, the implications of reduced recessing length and base layers in new pavement designs are subjected to meticulous scrutiny, shedding light on potential trade-offs between structural integrity and resource optimization.
Overall, the current thesis contributes to advancing pavement engineering practices, promoting sustainable transportation infrastructure, and supporting global sustainability goals. Through rigorous analysis and modelling, the research seeks to enhance the understanding of critical factors influencing widened pavement performance, paving the way for safer, more efficient, and environmentally conscious road networks.
This thesis shows the development of a singulation process for steel scrap particles. This singulation process is part of a sorting line that can sort scrap into different alloy types. This is an essential step in making steel a fully circular product. The new designs are based on an already existing chute used for aluminium singulation. In the report, the scrap properties and their behaviour on the aluminium chute are analysed. These insights are used to create three new designs for a chute that can be used for steel singulation. To evaluate these designs, a Discrete Element Method (DEM) model was used.
...
This thesis shows the development of a singulation process for steel scrap particles. This singulation process is part of a sorting line that can sort scrap into different alloy types. This is an essential step in making steel a fully circular product. The new designs are based on an already existing chute used for aluminium singulation. In the report, the scrap properties and their behaviour on the aluminium chute are analysed. These insights are used to create three new designs for a chute that can be used for steel singulation. To evaluate these designs, a Discrete Element Method (DEM) model was used.
Master thesis
(2024)
-
J. Fuertes, J.G. (Jan) Rots, Ir. Cor Kasbergen, A. (Alfonso) Prosperi, Ir. D. (Davide) Moretti, G. (Giovanna) Cera
Due to the Netherlands' topography and geology, many regions have weak soil resistance, causing numerous buildings to experience settlements from subsidence processes, with masonry structures being the most commonly affected. In these buildings, damage typically appears as cracks and deformations, indicating the foundation’s inability to support the structure. To enhance decision-making and the engineering of effective countermeasures in these scenarios, accurate and reliable building assessments are needed to predict the expected damage based on the amount of soil deformations. This thesis, therefore, aims to evaluate the capabilities of a set of state-of-the-art damage assessment methods. These methods have been applied to a case study, with their results benchmarked against evidence from a Building Foundation Assessment report, where recorded damage features were used to evaluate the accuracy and characteristics of each assessment method.
The study began with a Visual Assessment using a Decision Diagnostic Support Tool to analyze damage features and hypothesize the causes of the building's behavior. This was followed by an Empirical Assessment, applying empirical limits to relate expected damage to Subsidence-Related Intensity (SRI) parameters. Next, an Analytical Assessment used the Limit Tensile Strain Method (LTSM) to approximate building deformations, treating it as a linear-elastic isotropic masonry beam and correlating strain estimates to damage levels. Finally, a 2D Finite Element Analysis (FEA) using a continuum crack-modelling approach was conducted on the most damaged wall to more accurately reproduce the crack widths, crack locations and the behaviour of the wall.
The results show that while the building’s damage state can be approximated with reasonable accuracy, challenges remain in predicting specific damage features. The visual assessment successfully identified the building’s underlying mechanism. Empirical and analytical methods accurately predicted damage levels in 5 out of 6 walls, proving to be efficient assessment techniques. The 2D Finite Element Analysis (FEA) successfully simulated the crack pattern on Wall 2 with a Root Mean Square Error (RMSE) of +1 Ψ or +4.7mm against the maximum mean crack widths and reproduced 5 out of 7 cracks with similar characteristics. Additionally, FEA results showed that mesh sizes of 200, 100, and 50 mm made results deviate by σ = 0.33 Ψ and σCWmax = 2.3mm, with observable changes in crack shapes in EMM models.
To address the slight deviations in the less accurate analysis of the outer leaf, primarily driven by conservative crack width estimates, a Bayesian Optimization procedure was used on the outer leaf models to identify the optimal set of material parameters that minimized the discrepancy between the damage state of the results and the target damage level in the case study.
The implementation of the approach demonstrated sufficient efficiency in identifying the optimal set of parameters, despite the computational expense of the Finite Element models. The procedure’s effectiveness varied across models with it significantly reducing damage levels in the Engineering Masonry Model (EMM) variations but showed more limited improvements in the Total Strain Crack Model (TSCM). Additionally, the approach allowed for an investigation into the influence of material properties, revealing that Young's Modulus and tensile strength were the most influential parameters across both models. Furthermore, the results indicated that the influence of material parameters is highly non-linear, meaning changes in material properties do not always lead to predictable outcomes. Instead, specific combinations of parameters had a greater impact on reducing damage, demonstrating the complex interplay between material properties particularly in the EMM model variant.
...
The study began with a Visual Assessment using a Decision Diagnostic Support Tool to analyze damage features and hypothesize the causes of the building's behavior. This was followed by an Empirical Assessment, applying empirical limits to relate expected damage to Subsidence-Related Intensity (SRI) parameters. Next, an Analytical Assessment used the Limit Tensile Strain Method (LTSM) to approximate building deformations, treating it as a linear-elastic isotropic masonry beam and correlating strain estimates to damage levels. Finally, a 2D Finite Element Analysis (FEA) using a continuum crack-modelling approach was conducted on the most damaged wall to more accurately reproduce the crack widths, crack locations and the behaviour of the wall.
The results show that while the building’s damage state can be approximated with reasonable accuracy, challenges remain in predicting specific damage features. The visual assessment successfully identified the building’s underlying mechanism. Empirical and analytical methods accurately predicted damage levels in 5 out of 6 walls, proving to be efficient assessment techniques. The 2D Finite Element Analysis (FEA) successfully simulated the crack pattern on Wall 2 with a Root Mean Square Error (RMSE) of +1 Ψ or +4.7mm against the maximum mean crack widths and reproduced 5 out of 7 cracks with similar characteristics. Additionally, FEA results showed that mesh sizes of 200, 100, and 50 mm made results deviate by σ = 0.33 Ψ and σCWmax = 2.3mm, with observable changes in crack shapes in EMM models.
To address the slight deviations in the less accurate analysis of the outer leaf, primarily driven by conservative crack width estimates, a Bayesian Optimization procedure was used on the outer leaf models to identify the optimal set of material parameters that minimized the discrepancy between the damage state of the results and the target damage level in the case study.
The implementation of the approach demonstrated sufficient efficiency in identifying the optimal set of parameters, despite the computational expense of the Finite Element models. The procedure’s effectiveness varied across models with it significantly reducing damage levels in the Engineering Masonry Model (EMM) variations but showed more limited improvements in the Total Strain Crack Model (TSCM). Additionally, the approach allowed for an investigation into the influence of material properties, revealing that Young's Modulus and tensile strength were the most influential parameters across both models. Furthermore, the results indicated that the influence of material parameters is highly non-linear, meaning changes in material properties do not always lead to predictable outcomes. Instead, specific combinations of parameters had a greater impact on reducing damage, demonstrating the complex interplay between material properties particularly in the EMM model variant.
...
Due to the Netherlands' topography and geology, many regions have weak soil resistance, causing numerous buildings to experience settlements from subsidence processes, with masonry structures being the most commonly affected. In these buildings, damage typically appears as cracks and deformations, indicating the foundation’s inability to support the structure. To enhance decision-making and the engineering of effective countermeasures in these scenarios, accurate and reliable building assessments are needed to predict the expected damage based on the amount of soil deformations. This thesis, therefore, aims to evaluate the capabilities of a set of state-of-the-art damage assessment methods. These methods have been applied to a case study, with their results benchmarked against evidence from a Building Foundation Assessment report, where recorded damage features were used to evaluate the accuracy and characteristics of each assessment method.
The study began with a Visual Assessment using a Decision Diagnostic Support Tool to analyze damage features and hypothesize the causes of the building's behavior. This was followed by an Empirical Assessment, applying empirical limits to relate expected damage to Subsidence-Related Intensity (SRI) parameters. Next, an Analytical Assessment used the Limit Tensile Strain Method (LTSM) to approximate building deformations, treating it as a linear-elastic isotropic masonry beam and correlating strain estimates to damage levels. Finally, a 2D Finite Element Analysis (FEA) using a continuum crack-modelling approach was conducted on the most damaged wall to more accurately reproduce the crack widths, crack locations and the behaviour of the wall.
The results show that while the building’s damage state can be approximated with reasonable accuracy, challenges remain in predicting specific damage features. The visual assessment successfully identified the building’s underlying mechanism. Empirical and analytical methods accurately predicted damage levels in 5 out of 6 walls, proving to be efficient assessment techniques. The 2D Finite Element Analysis (FEA) successfully simulated the crack pattern on Wall 2 with a Root Mean Square Error (RMSE) of +1 Ψ or +4.7mm against the maximum mean crack widths and reproduced 5 out of 7 cracks with similar characteristics. Additionally, FEA results showed that mesh sizes of 200, 100, and 50 mm made results deviate by σ = 0.33 Ψ and σCWmax = 2.3mm, with observable changes in crack shapes in EMM models.
To address the slight deviations in the less accurate analysis of the outer leaf, primarily driven by conservative crack width estimates, a Bayesian Optimization procedure was used on the outer leaf models to identify the optimal set of material parameters that minimized the discrepancy between the damage state of the results and the target damage level in the case study.
The implementation of the approach demonstrated sufficient efficiency in identifying the optimal set of parameters, despite the computational expense of the Finite Element models. The procedure’s effectiveness varied across models with it significantly reducing damage levels in the Engineering Masonry Model (EMM) variations but showed more limited improvements in the Total Strain Crack Model (TSCM). Additionally, the approach allowed for an investigation into the influence of material properties, revealing that Young's Modulus and tensile strength were the most influential parameters across both models. Furthermore, the results indicated that the influence of material parameters is highly non-linear, meaning changes in material properties do not always lead to predictable outcomes. Instead, specific combinations of parameters had a greater impact on reducing damage, demonstrating the complex interplay between material properties particularly in the EMM model variant.
The study began with a Visual Assessment using a Decision Diagnostic Support Tool to analyze damage features and hypothesize the causes of the building's behavior. This was followed by an Empirical Assessment, applying empirical limits to relate expected damage to Subsidence-Related Intensity (SRI) parameters. Next, an Analytical Assessment used the Limit Tensile Strain Method (LTSM) to approximate building deformations, treating it as a linear-elastic isotropic masonry beam and correlating strain estimates to damage levels. Finally, a 2D Finite Element Analysis (FEA) using a continuum crack-modelling approach was conducted on the most damaged wall to more accurately reproduce the crack widths, crack locations and the behaviour of the wall.
The results show that while the building’s damage state can be approximated with reasonable accuracy, challenges remain in predicting specific damage features. The visual assessment successfully identified the building’s underlying mechanism. Empirical and analytical methods accurately predicted damage levels in 5 out of 6 walls, proving to be efficient assessment techniques. The 2D Finite Element Analysis (FEA) successfully simulated the crack pattern on Wall 2 with a Root Mean Square Error (RMSE) of +1 Ψ or +4.7mm against the maximum mean crack widths and reproduced 5 out of 7 cracks with similar characteristics. Additionally, FEA results showed that mesh sizes of 200, 100, and 50 mm made results deviate by σ = 0.33 Ψ and σCWmax = 2.3mm, with observable changes in crack shapes in EMM models.
To address the slight deviations in the less accurate analysis of the outer leaf, primarily driven by conservative crack width estimates, a Bayesian Optimization procedure was used on the outer leaf models to identify the optimal set of material parameters that minimized the discrepancy between the damage state of the results and the target damage level in the case study.
The implementation of the approach demonstrated sufficient efficiency in identifying the optimal set of parameters, despite the computational expense of the Finite Element models. The procedure’s effectiveness varied across models with it significantly reducing damage levels in the Engineering Masonry Model (EMM) variations but showed more limited improvements in the Total Strain Crack Model (TSCM). Additionally, the approach allowed for an investigation into the influence of material properties, revealing that Young's Modulus and tensile strength were the most influential parameters across both models. Furthermore, the results indicated that the influence of material parameters is highly non-linear, meaning changes in material properties do not always lead to predictable outcomes. Instead, specific combinations of parameters had a greater impact on reducing damage, demonstrating the complex interplay between material properties particularly in the EMM model variant.
The utilization of Recycled Coarse Aggregate (RCA) in concrete has gained signifi-cant traction due to its environmental and economic advantages. However, ensuring the quality of RCA poses challenges as it is influenced by various unpredictable factors includ-ing the high water absorption of RCA, ineffective recycling processes, and the presence of contaminants. The existing body of research on the influence of RCA on the Compressive Strength (CS) of concrete has yielded inconsistent findings, and limited knowledge exists regarding the specific combination of parameters that enable effective control over CS. To address this gap, the present study aims to identify the essential parameters that contribute to controlling CS in concrete through the development of a predictive model. By investigat-ing these crucial parameters, this research intends to extent current knowledge on optimiz-ing the use of RCA in concrete.
To investigate the impact of the crucial parameters on the CS of concrete when uti-lizing RCA, a series of experiments were conducted. The RCA was obtained through the selective demolition recycling technique. The content of RCA was divided through manual separation into unbound stones, Low-Quality Recycled Aggregate (LQRA), and contami-nants. LQRA is composed of residual mortar and stones with mortar attached to their sur-face. The experiments included physical properties tests and optimization of the concrete mix designs. Additionally, relevant literature was consulted to identify the parameters that would serve as variables in constructing the predictive model. Through analysis via re-sponse surface methodology, a predictive model was developed to assess the impact of these critical parameters on the CS of concrete.
The experimental findings confirmed the statistical significance of the predictive model in assessing the impact of critical parameters on the CS of concrete. The level of LQRA was found to have a negative impact on the quality of RCA. The water-to-cement ratio was identified as a significant factor affecting the CS of concrete, with lower ratios yielding higher CS. When using RCA with high LQRA content (up to 65% of the total weight of RCA) as a substitute for natural coarse aggregate, higher replacement ratios re-sulted in lower CS.
In order to further validate the predictive model, Artificial Neural Network (ANN) modelling was incorporated as a non-linear method of assessing the relationship between the variables and the output, which is the CS. The high R2 values obtained from the ANN model demonstrated the robust alignment between the model and the data, strengthening its reliability. The integration of a Pareto chart and model-fitting regression gives a better physical understanding of the results of the predictive model by identifying influential terms and reducing complexity. The resulting model improves interpretability and predic-tive accuracy. The analyses emphasize the significance of integrating ANN and the Pareto chart approach in enhancing model validation and simplification.
These findings offer valuable insights into the parameters that are crucial to the CS of concrete which consists of RCA. By implementing the procedures that assess the quality of RCA, sustainable construction practices can be promoted, and the wider application of RCA can be facilitated on an industrial scale.
...
To investigate the impact of the crucial parameters on the CS of concrete when uti-lizing RCA, a series of experiments were conducted. The RCA was obtained through the selective demolition recycling technique. The content of RCA was divided through manual separation into unbound stones, Low-Quality Recycled Aggregate (LQRA), and contami-nants. LQRA is composed of residual mortar and stones with mortar attached to their sur-face. The experiments included physical properties tests and optimization of the concrete mix designs. Additionally, relevant literature was consulted to identify the parameters that would serve as variables in constructing the predictive model. Through analysis via re-sponse surface methodology, a predictive model was developed to assess the impact of these critical parameters on the CS of concrete.
The experimental findings confirmed the statistical significance of the predictive model in assessing the impact of critical parameters on the CS of concrete. The level of LQRA was found to have a negative impact on the quality of RCA. The water-to-cement ratio was identified as a significant factor affecting the CS of concrete, with lower ratios yielding higher CS. When using RCA with high LQRA content (up to 65% of the total weight of RCA) as a substitute for natural coarse aggregate, higher replacement ratios re-sulted in lower CS.
In order to further validate the predictive model, Artificial Neural Network (ANN) modelling was incorporated as a non-linear method of assessing the relationship between the variables and the output, which is the CS. The high R2 values obtained from the ANN model demonstrated the robust alignment between the model and the data, strengthening its reliability. The integration of a Pareto chart and model-fitting regression gives a better physical understanding of the results of the predictive model by identifying influential terms and reducing complexity. The resulting model improves interpretability and predic-tive accuracy. The analyses emphasize the significance of integrating ANN and the Pareto chart approach in enhancing model validation and simplification.
These findings offer valuable insights into the parameters that are crucial to the CS of concrete which consists of RCA. By implementing the procedures that assess the quality of RCA, sustainable construction practices can be promoted, and the wider application of RCA can be facilitated on an industrial scale.
...
The utilization of Recycled Coarse Aggregate (RCA) in concrete has gained signifi-cant traction due to its environmental and economic advantages. However, ensuring the quality of RCA poses challenges as it is influenced by various unpredictable factors includ-ing the high water absorption of RCA, ineffective recycling processes, and the presence of contaminants. The existing body of research on the influence of RCA on the Compressive Strength (CS) of concrete has yielded inconsistent findings, and limited knowledge exists regarding the specific combination of parameters that enable effective control over CS. To address this gap, the present study aims to identify the essential parameters that contribute to controlling CS in concrete through the development of a predictive model. By investigat-ing these crucial parameters, this research intends to extent current knowledge on optimiz-ing the use of RCA in concrete.
To investigate the impact of the crucial parameters on the CS of concrete when uti-lizing RCA, a series of experiments were conducted. The RCA was obtained through the selective demolition recycling technique. The content of RCA was divided through manual separation into unbound stones, Low-Quality Recycled Aggregate (LQRA), and contami-nants. LQRA is composed of residual mortar and stones with mortar attached to their sur-face. The experiments included physical properties tests and optimization of the concrete mix designs. Additionally, relevant literature was consulted to identify the parameters that would serve as variables in constructing the predictive model. Through analysis via re-sponse surface methodology, a predictive model was developed to assess the impact of these critical parameters on the CS of concrete.
The experimental findings confirmed the statistical significance of the predictive model in assessing the impact of critical parameters on the CS of concrete. The level of LQRA was found to have a negative impact on the quality of RCA. The water-to-cement ratio was identified as a significant factor affecting the CS of concrete, with lower ratios yielding higher CS. When using RCA with high LQRA content (up to 65% of the total weight of RCA) as a substitute for natural coarse aggregate, higher replacement ratios re-sulted in lower CS.
In order to further validate the predictive model, Artificial Neural Network (ANN) modelling was incorporated as a non-linear method of assessing the relationship between the variables and the output, which is the CS. The high R2 values obtained from the ANN model demonstrated the robust alignment between the model and the data, strengthening its reliability. The integration of a Pareto chart and model-fitting regression gives a better physical understanding of the results of the predictive model by identifying influential terms and reducing complexity. The resulting model improves interpretability and predic-tive accuracy. The analyses emphasize the significance of integrating ANN and the Pareto chart approach in enhancing model validation and simplification.
These findings offer valuable insights into the parameters that are crucial to the CS of concrete which consists of RCA. By implementing the procedures that assess the quality of RCA, sustainable construction practices can be promoted, and the wider application of RCA can be facilitated on an industrial scale.
To investigate the impact of the crucial parameters on the CS of concrete when uti-lizing RCA, a series of experiments were conducted. The RCA was obtained through the selective demolition recycling technique. The content of RCA was divided through manual separation into unbound stones, Low-Quality Recycled Aggregate (LQRA), and contami-nants. LQRA is composed of residual mortar and stones with mortar attached to their sur-face. The experiments included physical properties tests and optimization of the concrete mix designs. Additionally, relevant literature was consulted to identify the parameters that would serve as variables in constructing the predictive model. Through analysis via re-sponse surface methodology, a predictive model was developed to assess the impact of these critical parameters on the CS of concrete.
The experimental findings confirmed the statistical significance of the predictive model in assessing the impact of critical parameters on the CS of concrete. The level of LQRA was found to have a negative impact on the quality of RCA. The water-to-cement ratio was identified as a significant factor affecting the CS of concrete, with lower ratios yielding higher CS. When using RCA with high LQRA content (up to 65% of the total weight of RCA) as a substitute for natural coarse aggregate, higher replacement ratios re-sulted in lower CS.
In order to further validate the predictive model, Artificial Neural Network (ANN) modelling was incorporated as a non-linear method of assessing the relationship between the variables and the output, which is the CS. The high R2 values obtained from the ANN model demonstrated the robust alignment between the model and the data, strengthening its reliability. The integration of a Pareto chart and model-fitting regression gives a better physical understanding of the results of the predictive model by identifying influential terms and reducing complexity. The resulting model improves interpretability and predic-tive accuracy. The analyses emphasize the significance of integrating ANN and the Pareto chart approach in enhancing model validation and simplification.
These findings offer valuable insights into the parameters that are crucial to the CS of concrete which consists of RCA. By implementing the procedures that assess the quality of RCA, sustainable construction practices can be promoted, and the wider application of RCA can be facilitated on an industrial scale.
A predictive model of concrete compressive strength based on level of contamination of coarse aggregate
Experimental study and relation to the water absorption of the coarse aggregate
Recycled aggregate concrete is emphasized more and more nowadays due to its importance towards the construction industry and general welfare of our planet. Being such a significant feature with regard to universal sustainable development, every aspect of its properties should be evaluated, examined and optimized so that there is a well-known, well-described and ready to use product. This project aimed at correlating some of the established parameters of conventional concrete such as water absorption of the coarse aggregate fraction and the resulting compressing strength, only applied in the field of recycled aggregate concrete. Along with these two properties, a prediction model was sought for which would be able to forecast the mechanical strength of concrete based on its coarse aggregate composition. A series of experiments were performed on samples fabricated for water absorption tests and compressive strength assessment. In total, 112 water absorption samples and over 250 concrete specimens were prepared and examined for the respective attribute. These samples used natural aggregate as the base of the coarse aggregate portion of the mix design, alongside a series of so-called contaminants which replaced the gravel in certain concentrations. These contaminants included bricks, ceramic tiles, glass, wood, gypsum, plastics, mineral fibers and recycled sand concrete and were entirely based upon the C&DW composition globally. Further investigation was done on the inclusion of air within concrete so that contaminated concrete results could be equated to this constant. All water absorption tests were performed according to the current standards and concrete specimens were crushed after 7 and 28 days of curing in order to obtain their strength in compression, while the predictive model was initiated via the Minitab statistical software.
The results indicated some interesting and promising trends. From both sets of experiments, it was evident that the water absorption of the coarse aggregate fraction was not the main contributor towards the strength development of recycled concrete. It had a minor influence, especially compared to the type of contaminant present and how much volume it took. Furthermore, samples with identical water absorption fabricated concretes with different strengths. Overall, plastics and wood had the most negative effect in terms of compressive strength, while bricks, tiles and glass seemed to affect this aspect in neutral or even slightly positive manner. EPS foam in very limited amounts yielded a notable 30 to 35% strength drop, while on the other hand, brick replacing 20% of the NA improved the strength by approximately 7% after 7 days and 2% after 28 days. In the end, based on all experimental input, a predictive model was developed, optimized and validated in several steps so that it was able to predict the water absorption of coarse aggregate, compressive strength after 7 and 28 days and equivalent air content based on the composition of the coarse aggregates. The back-end of the model is provided within the report as a MATLAB code.
...
The results indicated some interesting and promising trends. From both sets of experiments, it was evident that the water absorption of the coarse aggregate fraction was not the main contributor towards the strength development of recycled concrete. It had a minor influence, especially compared to the type of contaminant present and how much volume it took. Furthermore, samples with identical water absorption fabricated concretes with different strengths. Overall, plastics and wood had the most negative effect in terms of compressive strength, while bricks, tiles and glass seemed to affect this aspect in neutral or even slightly positive manner. EPS foam in very limited amounts yielded a notable 30 to 35% strength drop, while on the other hand, brick replacing 20% of the NA improved the strength by approximately 7% after 7 days and 2% after 28 days. In the end, based on all experimental input, a predictive model was developed, optimized and validated in several steps so that it was able to predict the water absorption of coarse aggregate, compressive strength after 7 and 28 days and equivalent air content based on the composition of the coarse aggregates. The back-end of the model is provided within the report as a MATLAB code.
...
Recycled aggregate concrete is emphasized more and more nowadays due to its importance towards the construction industry and general welfare of our planet. Being such a significant feature with regard to universal sustainable development, every aspect of its properties should be evaluated, examined and optimized so that there is a well-known, well-described and ready to use product. This project aimed at correlating some of the established parameters of conventional concrete such as water absorption of the coarse aggregate fraction and the resulting compressing strength, only applied in the field of recycled aggregate concrete. Along with these two properties, a prediction model was sought for which would be able to forecast the mechanical strength of concrete based on its coarse aggregate composition. A series of experiments were performed on samples fabricated for water absorption tests and compressive strength assessment. In total, 112 water absorption samples and over 250 concrete specimens were prepared and examined for the respective attribute. These samples used natural aggregate as the base of the coarse aggregate portion of the mix design, alongside a series of so-called contaminants which replaced the gravel in certain concentrations. These contaminants included bricks, ceramic tiles, glass, wood, gypsum, plastics, mineral fibers and recycled sand concrete and were entirely based upon the C&DW composition globally. Further investigation was done on the inclusion of air within concrete so that contaminated concrete results could be equated to this constant. All water absorption tests were performed according to the current standards and concrete specimens were crushed after 7 and 28 days of curing in order to obtain their strength in compression, while the predictive model was initiated via the Minitab statistical software.
The results indicated some interesting and promising trends. From both sets of experiments, it was evident that the water absorption of the coarse aggregate fraction was not the main contributor towards the strength development of recycled concrete. It had a minor influence, especially compared to the type of contaminant present and how much volume it took. Furthermore, samples with identical water absorption fabricated concretes with different strengths. Overall, plastics and wood had the most negative effect in terms of compressive strength, while bricks, tiles and glass seemed to affect this aspect in neutral or even slightly positive manner. EPS foam in very limited amounts yielded a notable 30 to 35% strength drop, while on the other hand, brick replacing 20% of the NA improved the strength by approximately 7% after 7 days and 2% after 28 days. In the end, based on all experimental input, a predictive model was developed, optimized and validated in several steps so that it was able to predict the water absorption of coarse aggregate, compressive strength after 7 and 28 days and equivalent air content based on the composition of the coarse aggregates. The back-end of the model is provided within the report as a MATLAB code.
The results indicated some interesting and promising trends. From both sets of experiments, it was evident that the water absorption of the coarse aggregate fraction was not the main contributor towards the strength development of recycled concrete. It had a minor influence, especially compared to the type of contaminant present and how much volume it took. Furthermore, samples with identical water absorption fabricated concretes with different strengths. Overall, plastics and wood had the most negative effect in terms of compressive strength, while bricks, tiles and glass seemed to affect this aspect in neutral or even slightly positive manner. EPS foam in very limited amounts yielded a notable 30 to 35% strength drop, while on the other hand, brick replacing 20% of the NA improved the strength by approximately 7% after 7 days and 2% after 28 days. In the end, based on all experimental input, a predictive model was developed, optimized and validated in several steps so that it was able to predict the water absorption of coarse aggregate, compressive strength after 7 and 28 days and equivalent air content based on the composition of the coarse aggregates. The back-end of the model is provided within the report as a MATLAB code.
Optimizing the assessment of fatigue in inverted T-girder bridges
A parametric study of the factors influencing the fatigue analysis of concrete under compression
With the continuous increase in transportation volume, bridges face the challenge of carrying higher traffic loads. As a result, bridges undergo fatigue due to repeated and increasing loads, leading to progressive deterioration of their structural reliability. While existing codes already account for several variables affecting the concrete's ability to withstand compression fatigue, some critical factors are still not considered. Furthermore, the modelling aspects of Finite Element Analysis (FEA) are often simplified or disregarded in practical applications, leading to an inaccurate estimation of fatigue life for concrete. As a result, a considerable number of bridges may be rejected for fatigue despite the possibility that they are not susceptible to this issue.
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment. ...
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment. ...
With the continuous increase in transportation volume, bridges face the challenge of carrying higher traffic loads. As a result, bridges undergo fatigue due to repeated and increasing loads, leading to progressive deterioration of their structural reliability. While existing codes already account for several variables affecting the concrete's ability to withstand compression fatigue, some critical factors are still not considered. Furthermore, the modelling aspects of Finite Element Analysis (FEA) are often simplified or disregarded in practical applications, leading to an inaccurate estimation of fatigue life for concrete. As a result, a considerable number of bridges may be rejected for fatigue despite the possibility that they are not susceptible to this issue.
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment.
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment.
Master thesis
(2022)
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H.A.O. Richardson, P.C.J. Hoogenboom, A.C.W.M. Vrouwenvelder, W.A.A.M. Bierbooms, C. Kasbergen
A structural firm will not invest a large sum of money in early design fase on a wind tunnel aeroelastic model to determine the displacements, forces, and moments when the dimensions of a building have only been estimated because the outcomes are only valid for that specific model. It is well-known that the outcomes are hard to determine precisely in early design fase.
This study aims to make a modelling tool in Matlab to predict the bending and torsional oscillations of a high-rise building due to wind load fluctuations in time and space.
To test the research question, which is, does the designed Juffertoren building in Rotterdam and the structurally strengthened student building Voorhof in Delft comply in the serviceability limit state when looking at bending and torsion accelerations in the along wind direction.
After strengthening the occupants of the student building Voorhof still complained about motion sickness during storms.
The results show that the Juffertoren and the student building Voorhof do not meet the serviceability limit state requirement.
These results suggest that more research should be done when looking at serviceability limit state requirements by light weight and thin buildings.
...
This study aims to make a modelling tool in Matlab to predict the bending and torsional oscillations of a high-rise building due to wind load fluctuations in time and space.
To test the research question, which is, does the designed Juffertoren building in Rotterdam and the structurally strengthened student building Voorhof in Delft comply in the serviceability limit state when looking at bending and torsion accelerations in the along wind direction.
After strengthening the occupants of the student building Voorhof still complained about motion sickness during storms.
The results show that the Juffertoren and the student building Voorhof do not meet the serviceability limit state requirement.
These results suggest that more research should be done when looking at serviceability limit state requirements by light weight and thin buildings.
...
A structural firm will not invest a large sum of money in early design fase on a wind tunnel aeroelastic model to determine the displacements, forces, and moments when the dimensions of a building have only been estimated because the outcomes are only valid for that specific model. It is well-known that the outcomes are hard to determine precisely in early design fase.
This study aims to make a modelling tool in Matlab to predict the bending and torsional oscillations of a high-rise building due to wind load fluctuations in time and space.
To test the research question, which is, does the designed Juffertoren building in Rotterdam and the structurally strengthened student building Voorhof in Delft comply in the serviceability limit state when looking at bending and torsion accelerations in the along wind direction.
After strengthening the occupants of the student building Voorhof still complained about motion sickness during storms.
The results show that the Juffertoren and the student building Voorhof do not meet the serviceability limit state requirement.
These results suggest that more research should be done when looking at serviceability limit state requirements by light weight and thin buildings.
This study aims to make a modelling tool in Matlab to predict the bending and torsional oscillations of a high-rise building due to wind load fluctuations in time and space.
To test the research question, which is, does the designed Juffertoren building in Rotterdam and the structurally strengthened student building Voorhof in Delft comply in the serviceability limit state when looking at bending and torsion accelerations in the along wind direction.
After strengthening the occupants of the student building Voorhof still complained about motion sickness during storms.
The results show that the Juffertoren and the student building Voorhof do not meet the serviceability limit state requirement.
These results suggest that more research should be done when looking at serviceability limit state requirements by light weight and thin buildings.
The University of Twente performed experimental uniaxial compression tests of Poly(ether-ether-ketone) (PEEK) and the TU Delft made a comparison with a numerical model; the viscoplastic Eindhoven Glassy Polymer (EGP) model. A higher strain-rate dependency and a higher yield stress at lower temperatures are observed in the experimental results. It is of importance to correctly model the stress-strain behaviour of PEEK for future research in long term behaviour of fibre reinforced PEEK by adapting the EGP model to account for these differences. The viscosity of the EGP model is based on the Ree-Eyring equation in which the three Ree-Eyring parameters (activation volume, activation energy and initial viscosities) are constants within the EGP model. It is observed that all three Ree-Eyring parameters are not constant over the strain when the original Ree-Eyring equation is fitted to the experimental data. Thus, non-constant Ree-Eyring parameters should be included in the EGP model. Evolving all three Ree-Eyring parameters leads to accurate stress-strain results, except for the pre-yield regime. The EGP model does not behave as stiff as the experiment in this region. Thus, a higher stiffness is included by evolving the shear moduli over the pre-yield regime. The evolution of the Ree-Eyring parameters is expressed by a $\tanh()$ function and quadratic function, while the evolution of the shear moduli is only expressed by a $\tanh()$ function. The evolution based on the $\tanh()$ function mostly influences the behaviour at small strains and the evolution based on the quadratic function mostly influences the behaviour at large strains. The evolution of the Ree-Eyring parameters at large strains leads to the insertion of viscous strain hardening in the EGP model. The viscous strain hardening qualitatively describes the Bauschinger effect for a cyclic loading case. The Bauschinger effect can be explained as the change of material behaviour when stresses are present. What occurs when the loading direction reverses within a cyclic loading case. An invariant function that is proportional to the strain determines the strain dependency of the evolution of the Ree-Eyring parameters and shear moduli. This invariant function is prevented from reducing for the evolution based on the $\tanh()$ function when the loading direction is reversed but does reduce for the evolution based on the quadratic function to correctly model cyclic loading. Furthermore, the linearization of the stiffness tensor is updated for the changes to the EGP model and a part of the stiffness tensor which was omitted in the original implementation is added.
Including the evolution of the Ree-Eyring parameters and shear moduli with the mentioned characteristics in the EGP model makes the EGP model correspond very well with the experimental results for all investigated temperatures and strain-rates. ...
Including the evolution of the Ree-Eyring parameters and shear moduli with the mentioned characteristics in the EGP model makes the EGP model correspond very well with the experimental results for all investigated temperatures and strain-rates. ...
The University of Twente performed experimental uniaxial compression tests of Poly(ether-ether-ketone) (PEEK) and the TU Delft made a comparison with a numerical model; the viscoplastic Eindhoven Glassy Polymer (EGP) model. A higher strain-rate dependency and a higher yield stress at lower temperatures are observed in the experimental results. It is of importance to correctly model the stress-strain behaviour of PEEK for future research in long term behaviour of fibre reinforced PEEK by adapting the EGP model to account for these differences. The viscosity of the EGP model is based on the Ree-Eyring equation in which the three Ree-Eyring parameters (activation volume, activation energy and initial viscosities) are constants within the EGP model. It is observed that all three Ree-Eyring parameters are not constant over the strain when the original Ree-Eyring equation is fitted to the experimental data. Thus, non-constant Ree-Eyring parameters should be included in the EGP model. Evolving all three Ree-Eyring parameters leads to accurate stress-strain results, except for the pre-yield regime. The EGP model does not behave as stiff as the experiment in this region. Thus, a higher stiffness is included by evolving the shear moduli over the pre-yield regime. The evolution of the Ree-Eyring parameters is expressed by a $\tanh()$ function and quadratic function, while the evolution of the shear moduli is only expressed by a $\tanh()$ function. The evolution based on the $\tanh()$ function mostly influences the behaviour at small strains and the evolution based on the quadratic function mostly influences the behaviour at large strains. The evolution of the Ree-Eyring parameters at large strains leads to the insertion of viscous strain hardening in the EGP model. The viscous strain hardening qualitatively describes the Bauschinger effect for a cyclic loading case. The Bauschinger effect can be explained as the change of material behaviour when stresses are present. What occurs when the loading direction reverses within a cyclic loading case. An invariant function that is proportional to the strain determines the strain dependency of the evolution of the Ree-Eyring parameters and shear moduli. This invariant function is prevented from reducing for the evolution based on the $\tanh()$ function when the loading direction is reversed but does reduce for the evolution based on the quadratic function to correctly model cyclic loading. Furthermore, the linearization of the stiffness tensor is updated for the changes to the EGP model and a part of the stiffness tensor which was omitted in the original implementation is added.
Including the evolution of the Ree-Eyring parameters and shear moduli with the mentioned characteristics in the EGP model makes the EGP model correspond very well with the experimental results for all investigated temperatures and strain-rates.
Including the evolution of the Ree-Eyring parameters and shear moduli with the mentioned characteristics in the EGP model makes the EGP model correspond very well with the experimental results for all investigated temperatures and strain-rates.
Verification, Validation and Application of the NorSand Constitutive Model in PLAXIS
Single-stress point analyses of experimental lab test data and finite element analyses of a submerged landslide
Master thesis
(2021)
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L.J. Woudstra, R.B.J. Brinkgreve, Ferdinando Marinelli, M.A. Hicks, A.P. van den Eijnden, C. Kasbergen
As the construction of sub-aerial and submarine geotechnical structures increase in amount, rate and size, so do their associated risks. Often, with use constitutive models, finite element analyses (FEAs) are performed in order to identify and mitigate these risks. NorSand, which is a consti- tutive model based on critical state soil mechanics for particulate materials (e.g., sand), is one of the first models to integrate the state parameter ψ into its constitutive framework to model dense and loose sands material with the same parameter set. Importantly, it is able to identify the liquefaction potential as it can simulate softening behaviour due to pore pressure increase of loose soils in undrained conditions. Since NorSand has recently been implement into PLAXIS, a geotechnical analysis software capable of performing FEAs, it must be verified, validated and applied with the software, which is done in this report. First, stress-path and parametric analyses were conducted at single stress points. The stress- path analyses show how the state variables evolve for different triaxial conditions. Systematically changing the input parameters to extremes found in literature helped determine their influence on the evolution of stresses and strains. The resulting figures can be used to help future calibrations to experimental lab test data. The PLAXIS implemented NorSand (PLAXIS NorSand) was verified by comparing it with an implementation written in Visual Basic for Applications (VBA NorSand) by the authors of the model Jefferies and Been. Verification in this context means determining if PLAXIS NorSand is able to produce outputs as intended by the authors. Various testing conditions, both triaxial and direct simple shear, showed overlap and agreement between the outputs of both implementations, verifying PLAXIS NorSand. Then, the model was compared to, albeit not in a traditional sense, an ’analytical solution’, which is the relationship between the mobilized friction ratio Mi and state parameter ψ in its simplest form. The mobilized friction ratio and stress ratio at peak strength of PLAXIS NorSand and the ’analytical solution’ were compared. The values between both showed less than 3% difference, further verifying PLAXIS NorSand. The constitutive model was then validated - i.e., established that PLAXIS NorSand is able to approximate soil behaviour as intended. First, by using the soil parameter set that had been derived from lab tests of Erksak sand as a baseline, the input parameters were varied until PLAXIS NorSand was calibrated to individual triaxial tests as best as possible. Then, triaxial tests of Erksak, Nerlerk and Ticino sand were approximated with PLAXIS NorSand without changing the soil parameters determined from lab test data. PLAXIS NorSand is able to follow lab test data decently well with one parameter set. And if one decides to take the time and calibrate individual lab tests, and deviate from soil parameters determined from a set of lab tests, they can be matched even better. Additionally, it showed a consistent need for activation of the softening flag (S = 1) in order to appropriately model loose soils in undrained conditions. Furthermore, NorSand exhibits indefinite hardening in dense soils during undrained loading, which can be avoided by employing a ’cavitation cut-off’. The last part of this report tested PLAXIS NorSand by applying it in FEAs of a simplified submerged landslide, which was subjected to 20 centimeters of displacement at the crest through a rigid slab in undrained conditions. First, the difference in slope behaviour due to change in soil density within NorSand was determined: dense soil resulted in the slope to be able to bear the full 20 centimeter displacement, whereas increasing the void ratio (i.e., increasing the positive value for the state parameter) gave the effect of even quicker slope collapse and a lower bearing capacity. In other words, when using NorSand, the looser soil the further the failure surface moves up and the quicker the structure fails to maintain equilibrium. Lastly, NorSand was compared to Modified Cam-Clay and Mohr-Coulomb to highlight the differences in their ability to model static liquefaction, while being triggered by unrealistic loading conditions. Even though none of the FEAs showed actual liquefaction, since it is accompanied with the fluidization and loss of structure, they still gave in indication of the liquefaction potential. NorSand, contrary to the other constitutive models, showed the expected high sensitivity to forced displacement resulting in clear shear bands resembling Prandtl-type failure mechanism and early onset soil body collapse.
...
As the construction of sub-aerial and submarine geotechnical structures increase in amount, rate and size, so do their associated risks. Often, with use constitutive models, finite element analyses (FEAs) are performed in order to identify and mitigate these risks. NorSand, which is a consti- tutive model based on critical state soil mechanics for particulate materials (e.g., sand), is one of the first models to integrate the state parameter ψ into its constitutive framework to model dense and loose sands material with the same parameter set. Importantly, it is able to identify the liquefaction potential as it can simulate softening behaviour due to pore pressure increase of loose soils in undrained conditions. Since NorSand has recently been implement into PLAXIS, a geotechnical analysis software capable of performing FEAs, it must be verified, validated and applied with the software, which is done in this report. First, stress-path and parametric analyses were conducted at single stress points. The stress- path analyses show how the state variables evolve for different triaxial conditions. Systematically changing the input parameters to extremes found in literature helped determine their influence on the evolution of stresses and strains. The resulting figures can be used to help future calibrations to experimental lab test data. The PLAXIS implemented NorSand (PLAXIS NorSand) was verified by comparing it with an implementation written in Visual Basic for Applications (VBA NorSand) by the authors of the model Jefferies and Been. Verification in this context means determining if PLAXIS NorSand is able to produce outputs as intended by the authors. Various testing conditions, both triaxial and direct simple shear, showed overlap and agreement between the outputs of both implementations, verifying PLAXIS NorSand. Then, the model was compared to, albeit not in a traditional sense, an ’analytical solution’, which is the relationship between the mobilized friction ratio Mi and state parameter ψ in its simplest form. The mobilized friction ratio and stress ratio at peak strength of PLAXIS NorSand and the ’analytical solution’ were compared. The values between both showed less than 3% difference, further verifying PLAXIS NorSand. The constitutive model was then validated - i.e., established that PLAXIS NorSand is able to approximate soil behaviour as intended. First, by using the soil parameter set that had been derived from lab tests of Erksak sand as a baseline, the input parameters were varied until PLAXIS NorSand was calibrated to individual triaxial tests as best as possible. Then, triaxial tests of Erksak, Nerlerk and Ticino sand were approximated with PLAXIS NorSand without changing the soil parameters determined from lab test data. PLAXIS NorSand is able to follow lab test data decently well with one parameter set. And if one decides to take the time and calibrate individual lab tests, and deviate from soil parameters determined from a set of lab tests, they can be matched even better. Additionally, it showed a consistent need for activation of the softening flag (S = 1) in order to appropriately model loose soils in undrained conditions. Furthermore, NorSand exhibits indefinite hardening in dense soils during undrained loading, which can be avoided by employing a ’cavitation cut-off’. The last part of this report tested PLAXIS NorSand by applying it in FEAs of a simplified submerged landslide, which was subjected to 20 centimeters of displacement at the crest through a rigid slab in undrained conditions. First, the difference in slope behaviour due to change in soil density within NorSand was determined: dense soil resulted in the slope to be able to bear the full 20 centimeter displacement, whereas increasing the void ratio (i.e., increasing the positive value for the state parameter) gave the effect of even quicker slope collapse and a lower bearing capacity. In other words, when using NorSand, the looser soil the further the failure surface moves up and the quicker the structure fails to maintain equilibrium. Lastly, NorSand was compared to Modified Cam-Clay and Mohr-Coulomb to highlight the differences in their ability to model static liquefaction, while being triggered by unrealistic loading conditions. Even though none of the FEAs showed actual liquefaction, since it is accompanied with the fluidization and loss of structure, they still gave in indication of the liquefaction potential. NorSand, contrary to the other constitutive models, showed the expected high sensitivity to forced displacement resulting in clear shear bands resembling Prandtl-type failure mechanism and early onset soil body collapse.
Master thesis
(2021)
-
J. Trimarchi Maldonado, K. Anupam, S.M.J.G. Erkens, C. Kasbergen, A.A. Nunez Vicencio, Alessandro Marradi
Pavement structures are assessed based on its functional and structural capacity in order to evaluate the safety of its use. Structural pavement evaluation is often carried out by road authorities or consulting companies that use non-destructive testing (NDT) methods to assess the remaining life and structural capacity of a road structure at project or network level. In Western Europe and in most parts of the world, the most common equipment used as part of the NDT method is the use of the Falling Weight Deflectometer (FWD). The FWD is able to capture deflection values that can be used for the backcalculation of moduli and to determine remaining life of a structure by mechanistic-empirical equations.
In the Netherlands, like in many other countries, motorways have an increased number traffic flow based on high population densities accumulating in major cities. Due to this, pavement evaluation with stationary equipment such as the FWD can become relatively expensive due to the disruption of traffic. To solve this problem, research institutions and consulting companies have developed different versions of continuous evaluation equipment that are able to perform the structural analysis in a similar way to the FWD. In 2018, Dynatest® launched the Rapid Pavement Tester (RPT or RAPTOR) which aims to perform functional and structural evaluation of road networks at traffic speed. Continuous evaluation devices such as the RAPTOR are in constant development in order to achieve the quality and guaranty of use that equipment such as the FWD have in the pavement engineering industry. Currently this type of device uses technology that is less accurate than the sensors (Geophones) used in FWD equipment. This becomes a significant impediment in the evaluation of high stiffness pavement structures as the calculated deflections are in the lower end of the spectrum. This research aims to find a methodology that can be used in order to find limitation stiffness parameter values for which it is viable to use continuous evaluation equipment. Additionally, this research aims to find a method that can be used in the pavement engineering industry and research that is able to aid the data collection process of pavement layer information by means of machine learning tools. This was a problem faced during the elaboration of this research as the data collected to perform the analysis was incomplete in terms of layer thicknesses information. This process is carried by means of an artificial neural network (ANN) that is able to predict layer thicknesses and moduli based on deflection values and deflection parameters that obtained with the FWD.
The analysis of this research is carried by comparing deflection values in different road networks collected with the FWD and the RAPTOR under similar weather conditions, where the predicted layer information is used to assess the cut-off values and limitations that the current version of the RAPTOR has when compared to the FWD. From the presented results it was found that the asphalt layer modulus showed the highest correlation to the limitation values where the RAPTOR is able to present reliable results when compared to the FWD. Additionally, promising results were found in the use of ANN method to predict missing layer information which are assumed to improve with a specific build in the ANN architecture. ...
In the Netherlands, like in many other countries, motorways have an increased number traffic flow based on high population densities accumulating in major cities. Due to this, pavement evaluation with stationary equipment such as the FWD can become relatively expensive due to the disruption of traffic. To solve this problem, research institutions and consulting companies have developed different versions of continuous evaluation equipment that are able to perform the structural analysis in a similar way to the FWD. In 2018, Dynatest® launched the Rapid Pavement Tester (RPT or RAPTOR) which aims to perform functional and structural evaluation of road networks at traffic speed. Continuous evaluation devices such as the RAPTOR are in constant development in order to achieve the quality and guaranty of use that equipment such as the FWD have in the pavement engineering industry. Currently this type of device uses technology that is less accurate than the sensors (Geophones) used in FWD equipment. This becomes a significant impediment in the evaluation of high stiffness pavement structures as the calculated deflections are in the lower end of the spectrum. This research aims to find a methodology that can be used in order to find limitation stiffness parameter values for which it is viable to use continuous evaluation equipment. Additionally, this research aims to find a method that can be used in the pavement engineering industry and research that is able to aid the data collection process of pavement layer information by means of machine learning tools. This was a problem faced during the elaboration of this research as the data collected to perform the analysis was incomplete in terms of layer thicknesses information. This process is carried by means of an artificial neural network (ANN) that is able to predict layer thicknesses and moduli based on deflection values and deflection parameters that obtained with the FWD.
The analysis of this research is carried by comparing deflection values in different road networks collected with the FWD and the RAPTOR under similar weather conditions, where the predicted layer information is used to assess the cut-off values and limitations that the current version of the RAPTOR has when compared to the FWD. From the presented results it was found that the asphalt layer modulus showed the highest correlation to the limitation values where the RAPTOR is able to present reliable results when compared to the FWD. Additionally, promising results were found in the use of ANN method to predict missing layer information which are assumed to improve with a specific build in the ANN architecture. ...
Pavement structures are assessed based on its functional and structural capacity in order to evaluate the safety of its use. Structural pavement evaluation is often carried out by road authorities or consulting companies that use non-destructive testing (NDT) methods to assess the remaining life and structural capacity of a road structure at project or network level. In Western Europe and in most parts of the world, the most common equipment used as part of the NDT method is the use of the Falling Weight Deflectometer (FWD). The FWD is able to capture deflection values that can be used for the backcalculation of moduli and to determine remaining life of a structure by mechanistic-empirical equations.
In the Netherlands, like in many other countries, motorways have an increased number traffic flow based on high population densities accumulating in major cities. Due to this, pavement evaluation with stationary equipment such as the FWD can become relatively expensive due to the disruption of traffic. To solve this problem, research institutions and consulting companies have developed different versions of continuous evaluation equipment that are able to perform the structural analysis in a similar way to the FWD. In 2018, Dynatest® launched the Rapid Pavement Tester (RPT or RAPTOR) which aims to perform functional and structural evaluation of road networks at traffic speed. Continuous evaluation devices such as the RAPTOR are in constant development in order to achieve the quality and guaranty of use that equipment such as the FWD have in the pavement engineering industry. Currently this type of device uses technology that is less accurate than the sensors (Geophones) used in FWD equipment. This becomes a significant impediment in the evaluation of high stiffness pavement structures as the calculated deflections are in the lower end of the spectrum. This research aims to find a methodology that can be used in order to find limitation stiffness parameter values for which it is viable to use continuous evaluation equipment. Additionally, this research aims to find a method that can be used in the pavement engineering industry and research that is able to aid the data collection process of pavement layer information by means of machine learning tools. This was a problem faced during the elaboration of this research as the data collected to perform the analysis was incomplete in terms of layer thicknesses information. This process is carried by means of an artificial neural network (ANN) that is able to predict layer thicknesses and moduli based on deflection values and deflection parameters that obtained with the FWD.
The analysis of this research is carried by comparing deflection values in different road networks collected with the FWD and the RAPTOR under similar weather conditions, where the predicted layer information is used to assess the cut-off values and limitations that the current version of the RAPTOR has when compared to the FWD. From the presented results it was found that the asphalt layer modulus showed the highest correlation to the limitation values where the RAPTOR is able to present reliable results when compared to the FWD. Additionally, promising results were found in the use of ANN method to predict missing layer information which are assumed to improve with a specific build in the ANN architecture.
In the Netherlands, like in many other countries, motorways have an increased number traffic flow based on high population densities accumulating in major cities. Due to this, pavement evaluation with stationary equipment such as the FWD can become relatively expensive due to the disruption of traffic. To solve this problem, research institutions and consulting companies have developed different versions of continuous evaluation equipment that are able to perform the structural analysis in a similar way to the FWD. In 2018, Dynatest® launched the Rapid Pavement Tester (RPT or RAPTOR) which aims to perform functional and structural evaluation of road networks at traffic speed. Continuous evaluation devices such as the RAPTOR are in constant development in order to achieve the quality and guaranty of use that equipment such as the FWD have in the pavement engineering industry. Currently this type of device uses technology that is less accurate than the sensors (Geophones) used in FWD equipment. This becomes a significant impediment in the evaluation of high stiffness pavement structures as the calculated deflections are in the lower end of the spectrum. This research aims to find a methodology that can be used in order to find limitation stiffness parameter values for which it is viable to use continuous evaluation equipment. Additionally, this research aims to find a method that can be used in the pavement engineering industry and research that is able to aid the data collection process of pavement layer information by means of machine learning tools. This was a problem faced during the elaboration of this research as the data collected to perform the analysis was incomplete in terms of layer thicknesses information. This process is carried by means of an artificial neural network (ANN) that is able to predict layer thicknesses and moduli based on deflection values and deflection parameters that obtained with the FWD.
The analysis of this research is carried by comparing deflection values in different road networks collected with the FWD and the RAPTOR under similar weather conditions, where the predicted layer information is used to assess the cut-off values and limitations that the current version of the RAPTOR has when compared to the FWD. From the presented results it was found that the asphalt layer modulus showed the highest correlation to the limitation values where the RAPTOR is able to present reliable results when compared to the FWD. Additionally, promising results were found in the use of ANN method to predict missing layer information which are assumed to improve with a specific build in the ANN architecture.
Influence of Numerical Size Effect in Non-Linear Finite Element Analysis
Investigation of Different Configurations of Iterative-Incremental Method for Shear Failure Mode of Reinforced Concrete without Shear Reinforcement
In concrete structures, shear failure is one of the failure mechanisms that should be estimated carefully due to its brittle nature. As the technology advances, the capacity of shear in concrete structures can be calculated with the analytical formulation in codes and standards and simulated with NLFEA. The shear capacity is affected by the size which is a phenomenon observed from experiments where the change in the structure size does not have a linear relation to the structural strength. This can be referred to as the experimental size effect. When estimating the shear capacity with NLFEA, this effect must be included in order to avoid over-estimation of capacity. However, another size effect can be found from the result of NLFEA. The change in structural size has an influence on the global response of concrete structures with different numerical configurations in a simulation with NLFEA. A numerical configuration consists of several numerical parameters. This effect is referred to as the numerical size effect. Therefore, it is necessary to incorporate the experimental size effect and reduce the influence of the numerical size effect in a numerical model in order to increase the accuracy and precision of the simulation with NLFEA.
The aim of this study is to investigate how the numerical size effect influences the NLFEA results, which will help understand how to improve the accuracy of the simulation. The investigation is done by studying numerical models with a variation on several numerical parameters, such as load increment, error tolerance, the maximum number of iterations and mesh size. The study is focused on identifying the influence of these numerical parameters for cases with different structural sizes and comparable shear slenderness. This is done by observing the global behaviour of the structure and comparing NLFEA results to their respective experimental results. Any difference in the simulated global response is analysed by observing the difference between the experimental and the simulated crack pattern and the convergence state of the respective step.
The study is done in three stages. The study is initiated by investigating how the flexural shear failure mode can be obtained with NLFEA. Two specimens with comparable shear slenderness (a/d), 3.70 and 3.91 for beam A123A1 and H123A respectively, are used as a reference for the simulation model. It was found that bad convergence was achieved at the later stage of the analysis and by not accepting non-converged steps, the results became dependent on the convergence state of the analysis where different peak loads were achieved in different numerical configurations for the same case study.
The study continues by identifying the correlation of numerical parameters with the results of NLFEA by creating simulation models with different iterative incremental solutions, load increment, error tolerance, and the maximum number of iterations. All load steps are accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models. The NLFEA results are post-processed by setting up an upper limit in the error tolerance in order to minimize the variation of the peak load and attain a higher consistency of the results.
At the last stage, another study is performed to identify the correlation between mesh sizes with the results of NLFEA by simulating several models with different mesh sizes. All load steps are also accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models The NLFEA results are also post-processed with the same criteria attained in the previous stage.
It is concluded that the results of NLFEA are dependent on the following numerical parameters, the load increment, error tolerance, and the maximum number of iterations, due to different initiations and propagation of dowel crack in the non-converged steps, which influences the convergence condition in the later stage of the NLFEA. The formation and rapid propagation of the dowel crack results in the excessive change in the principal strain direction and magnitude, which induces high relative energy variation and out-of-balance force. These numerical parameters indirectly contribute to the error found in each step in the analysis. An additional study is done by replacing the crack model with a fixed crack model with a damage-based shear retention model, but it was found that this did not solve the problem due to the excessive change in the shear retention factor on the elements that lead to premature failure of the beam.
The observation related to the numerical size effect reveals that the mesh size controls the propagation rate of the dowel crack. The use of a smaller mesh size will reduce the propagation rate of the dowel crack after its initiation due to a smaller increment of the crack width between each load step. As a result, the increment of the crack width becomes smaller as the mesh size decrease. This becomes more pronounced due to the effect of excessive change of the principal stress-strain direction and magnitude.
Full Newton-Raphson method has been proven to give the smallest variation of the peak load ratio (Pnorm), ranging from 0.887-1.140 for specimen A123A1 and 1.055-1.246 for specimen H123A, compared to the other iterative-incremental method with the use of load increment ratio (load increment/experimental peak load) within 0.03-0.006 in combination with evaluation of acceptable analysis step with error tolerance, where the predefined error tolerance must be set to Gerr = 0.0001 and Ferr = 0.01, and non-converged steps can still be accepted if the relative energy variation and out-of-balance force of the corresponding step are below 0.03 and 0.58 respectively.
An additional criterion related to the shear displacement on the major flexural shear crack (Δ) should be added to the evaluation of the acceptable analysis step in order to prevent an excessive crack opening on the major flexural shear crack at the peak load. The analysis step can still be considered valid if the respective step satisfies the criterion of the error tolerance and the vertical crack opening on the major flexural crack on the respective step is below the ultimate tensile crack width (CWt,u), which can be calculated from the Guidelines for Nonlinear Finite Element Analysis of Concrete Structures (Hendriks & Roosen, 2020). A mesh size ratio which larger than h/15 is required to have the correct simulated failure.
...
In concrete structures, shear failure is one of the failure mechanisms that should be estimated carefully due to its brittle nature. As the technology advances, the capacity of shear in concrete structures can be calculated with the analytical formulation in codes and standards and simulated with NLFEA. The shear capacity is affected by the size which is a phenomenon observed from experiments where the change in the structure size does not have a linear relation to the structural strength. This can be referred to as the experimental size effect. When estimating the shear capacity with NLFEA, this effect must be included in order to avoid over-estimation of capacity. However, another size effect can be found from the result of NLFEA. The change in structural size has an influence on the global response of concrete structures with different numerical configurations in a simulation with NLFEA. A numerical configuration consists of several numerical parameters. This effect is referred to as the numerical size effect. Therefore, it is necessary to incorporate the experimental size effect and reduce the influence of the numerical size effect in a numerical model in order to increase the accuracy and precision of the simulation with NLFEA.
The aim of this study is to investigate how the numerical size effect influences the NLFEA results, which will help understand how to improve the accuracy of the simulation. The investigation is done by studying numerical models with a variation on several numerical parameters, such as load increment, error tolerance, the maximum number of iterations and mesh size. The study is focused on identifying the influence of these numerical parameters for cases with different structural sizes and comparable shear slenderness. This is done by observing the global behaviour of the structure and comparing NLFEA results to their respective experimental results. Any difference in the simulated global response is analysed by observing the difference between the experimental and the simulated crack pattern and the convergence state of the respective step.
The study is done in three stages. The study is initiated by investigating how the flexural shear failure mode can be obtained with NLFEA. Two specimens with comparable shear slenderness (a/d), 3.70 and 3.91 for beam A123A1 and H123A respectively, are used as a reference for the simulation model. It was found that bad convergence was achieved at the later stage of the analysis and by not accepting non-converged steps, the results became dependent on the convergence state of the analysis where different peak loads were achieved in different numerical configurations for the same case study.
The study continues by identifying the correlation of numerical parameters with the results of NLFEA by creating simulation models with different iterative incremental solutions, load increment, error tolerance, and the maximum number of iterations. All load steps are accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models. The NLFEA results are post-processed by setting up an upper limit in the error tolerance in order to minimize the variation of the peak load and attain a higher consistency of the results.
At the last stage, another study is performed to identify the correlation between mesh sizes with the results of NLFEA by simulating several models with different mesh sizes. All load steps are also accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models The NLFEA results are also post-processed with the same criteria attained in the previous stage.
It is concluded that the results of NLFEA are dependent on the following numerical parameters, the load increment, error tolerance, and the maximum number of iterations, due to different initiations and propagation of dowel crack in the non-converged steps, which influences the convergence condition in the later stage of the NLFEA. The formation and rapid propagation of the dowel crack results in the excessive change in the principal strain direction and magnitude, which induces high relative energy variation and out-of-balance force. These numerical parameters indirectly contribute to the error found in each step in the analysis. An additional study is done by replacing the crack model with a fixed crack model with a damage-based shear retention model, but it was found that this did not solve the problem due to the excessive change in the shear retention factor on the elements that lead to premature failure of the beam.
The observation related to the numerical size effect reveals that the mesh size controls the propagation rate of the dowel crack. The use of a smaller mesh size will reduce the propagation rate of the dowel crack after its initiation due to a smaller increment of the crack width between each load step. As a result, the increment of the crack width becomes smaller as the mesh size decrease. This becomes more pronounced due to the effect of excessive change of the principal stress-strain direction and magnitude.
Full Newton-Raphson method has been proven to give the smallest variation of the peak load ratio (Pnorm), ranging from 0.887-1.140 for specimen A123A1 and 1.055-1.246 for specimen H123A, compared to the other iterative-incremental method with the use of load increment ratio (load increment/experimental peak load) within 0.03-0.006 in combination with evaluation of acceptable analysis step with error tolerance, where the predefined error tolerance must be set to Gerr = 0.0001 and Ferr = 0.01, and non-converged steps can still be accepted if the relative energy variation and out-of-balance force of the corresponding step are below 0.03 and 0.58 respectively.
An additional criterion related to the shear displacement on the major flexural shear crack (Δ) should be added to the evaluation of the acceptable analysis step in order to prevent an excessive crack opening on the major flexural shear crack at the peak load. The analysis step can still be considered valid if the respective step satisfies the criterion of the error tolerance and the vertical crack opening on the major flexural crack on the respective step is below the ultimate tensile crack width (CWt,u), which can be calculated from the Guidelines for Nonlinear Finite Element Analysis of Concrete Structures (Hendriks & Roosen, 2020). A mesh size ratio which larger than h/15 is required to have the correct simulated failure.
The fatigue life of asphalt concrete is an important parameter in the functional design of a road construction. In the Netherlands it is determined by the four Point Bending (4PB) test on laboratory prepared specimen. During the past years there is an increase in desire to validate the laid down asphalt pavement to the established functional properties. The most practical test setup applicable is theCyclic Indirect Tensile Test (CY-ITT). Both fatigue tests differ on many fronts from each other. The resulting traditional fatigue line between them is therefore not coherent. A solution is previously sought in applying the energy based method of the Ratio of Dissipated Energy Change (RDEC). Developedby Shen & Carpenter. This research is a continuation of those works. The objective of this research is therefore formulated as follows: Establishing a fatigue life relation through the energy methods, which couples the fatigue life results of both the CY-ITT and 4PB fatigue tests and preserve the asphalt mixture characteristics.In total 12 different mixtures were used to establish a wide field of mixture variation. Differences in RAP content, bitumen, PEN-grade and max aggregate size were used. Each mixture was tested on both force controlled CY-ITT and displacement controlled 4PB. Additional 4PB force controlled and Uni-axial displacement controlled fatigue tests were conducted on a single mixture.The results were analysed by the two main energy methods: The RDEC and the Viscous-Elastic Continuum Damage (VECD) model of Kim. The RDEC method is based on the slope ratio of the dissipated energy. The dissipated energy is calculated by the hysteresis loop. The VECD method is based on thelinearization of the strain by the pseudostrain energy function. The rate of the pseudostrain energy function (GR) is then used for the fatigue relation.For the RDEC is concluded that the method is a single line relationship. Independent of frequency, temperature, mixture type, mixture density and stress strain relation for each mode of loading. The test setup independence between the CY-ITT and 4PB was found for 6 out of the 12 mixtures. The 4PB force controlled test did not deliver an evident result. The Uni-axial displacement controlled fatigue test validated the RDEC independence of test setup. It is therefore not recommended to use the RDEC in the current configuration as a practical application for validation between laboratory prepared specimen and the road constructed asphalt concrete layer.For the VECD is concluded that the CY-ITT and 4PB did not form a single coherent fatigue line in the log(GR − NfatSN) relation. The relation is for a single test setup however mixture type dependent. The hypothesis that the fatigue line is dependent on the linear stiffness from the frequency sweep and could be shifted similar as on the mastercurve, proved preliminary to be true for the same test setup. However to be untrue between the CY-ITT and 4PB GR fatigue relation. The used relation between log(GR−NfatSN) is therefor not applicable in linking the CY-ITT and 4PB fatigue test setups.
...
The fatigue life of asphalt concrete is an important parameter in the functional design of a road construction. In the Netherlands it is determined by the four Point Bending (4PB) test on laboratory prepared specimen. During the past years there is an increase in desire to validate the laid down asphalt pavement to the established functional properties. The most practical test setup applicable is theCyclic Indirect Tensile Test (CY-ITT). Both fatigue tests differ on many fronts from each other. The resulting traditional fatigue line between them is therefore not coherent. A solution is previously sought in applying the energy based method of the Ratio of Dissipated Energy Change (RDEC). Developedby Shen & Carpenter. This research is a continuation of those works. The objective of this research is therefore formulated as follows: Establishing a fatigue life relation through the energy methods, which couples the fatigue life results of both the CY-ITT and 4PB fatigue tests and preserve the asphalt mixture characteristics.In total 12 different mixtures were used to establish a wide field of mixture variation. Differences in RAP content, bitumen, PEN-grade and max aggregate size were used. Each mixture was tested on both force controlled CY-ITT and displacement controlled 4PB. Additional 4PB force controlled and Uni-axial displacement controlled fatigue tests were conducted on a single mixture.The results were analysed by the two main energy methods: The RDEC and the Viscous-Elastic Continuum Damage (VECD) model of Kim. The RDEC method is based on the slope ratio of the dissipated energy. The dissipated energy is calculated by the hysteresis loop. The VECD method is based on thelinearization of the strain by the pseudostrain energy function. The rate of the pseudostrain energy function (GR) is then used for the fatigue relation.For the RDEC is concluded that the method is a single line relationship. Independent of frequency, temperature, mixture type, mixture density and stress strain relation for each mode of loading. The test setup independence between the CY-ITT and 4PB was found for 6 out of the 12 mixtures. The 4PB force controlled test did not deliver an evident result. The Uni-axial displacement controlled fatigue test validated the RDEC independence of test setup. It is therefore not recommended to use the RDEC in the current configuration as a practical application for validation between laboratory prepared specimen and the road constructed asphalt concrete layer.For the VECD is concluded that the CY-ITT and 4PB did not form a single coherent fatigue line in the log(GR − NfatSN) relation. The relation is for a single test setup however mixture type dependent. The hypothesis that the fatigue line is dependent on the linear stiffness from the frequency sweep and could be shifted similar as on the mastercurve, proved preliminary to be true for the same test setup. However to be untrue between the CY-ITT and 4PB GR fatigue relation. The used relation between log(GR−NfatSN) is therefor not applicable in linking the CY-ITT and 4PB fatigue test setups.
Master thesis
(2020)
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Rosanne Verloop, Wout Broere, Ronald Brinkgreve, Cor Kasbergen, Hans Mortier, Marijn Brugman
During the boring of a tunnel in soft soils with a slurry TBM, support pressure is used to achieve equilibrium at the face of the TBM. When this equilibrium is not reached, when the face support pressure is too low or too high, settlements will occur. In this research settlement and pore water pressure measurements are used to monitor the behavior of the soil and estimate the stability of the tunnel face. During boring of the tunnel, the exact stability of the face is not known. The TBM driver has to rely on the provided stratigraphy data, the advised face support pressures range provided by the geotechnical engineers and the experience of the tunnel boring team. Monitoring is not yet used to determine the face stability during construction. To do so, field data from a case study at RijnlandRoute is compared with analytical and numerical models. Sensitivity of the measurement equipment, and of both the analytical (DIN) and numerical model (Plaxis 3D) with respect to soil parameters, are considered. It has been found that the strength parameters of the layer in which the face is located have the highest influence on the minimum face support pressure. For the maximum face support pressure this is the volumetric weight of the entire soil profile above the face. For comparing the (soft soil) field data with numerical results, a Plaxis 3D model is built, and it is determined that HSsmall is a suitable constitutive model to capture the interaction between face stability, tunneling operations and soil behavior. It is shown that the tail void injection influences the settlements above and in front of the cutter head, but this influence is discarded and replaced by a wished in place lining, to simplify the numerical model. A scenario analysis on the sensitivity of soil parameters shows settlements do not vary significantly between the characteristic low and high values. In this analysis correlation of parameters is taken into account. The failure mechanism for the minimum face support pressure coincides with the active cave-in failure mechanism found in literature. For the maximum face support pressure the failure mechanism found in Plaxis 3D does not coincide with the expected hydraulic fracturing failure mode. The continuum representation of the soil in Plaxis 3D does not allow a hydraulic fracturing like failure mechanism to develop. Instead, a blow-out approximately 10 m. in front of the cutterhead occurs. This behaviour better resembles the failure mechanism of a EPB TBM. The field data gathered from the case study shows a thrust wave in front of the cutter head in both settlement and pore water pressure measurements. This thrust wave reaches up to 20 to 40 meters in front of the TBM. The heave induced by the thrust wave reduces the amount of settlements after the TBM passage. Excess pore pressures, induced by a high thrust wave, affect the face stability negatively. The excess pore pressure mainly depends on the advance rate. The higher the advance rate, the less time the pore pressures have to dissipate, leading to an increase in excess pore pressure. The accuracy of the settlements measurement devices is 0.8 mm., and of the spade cells 1.0 kPa. In general, the field data shows settlement curves corresponding to the Peck (1969) Gaussian curve (in lateral and longitudinal direction). Comparing the case study settlements with the numerically generated settlement curves show similar trends. The field data shows lower settlements than the numerical results. This can be due to the presence of excess pore pressures, the accuracy of the TBM data or its interpretation. A method to increase the accuracy, which is expected to result in a better fit with the numerical results, was found in a late phase of the research. This method takes into account the settlements which are induced by the thrust wave in front of the TBM. Comparing the numerical and analytically determined limit support pressures, it is found that the minimum face support pressure are similar in both methods. As similar failure mechanisms are found, numerical modelling seems a reliable way of determining the face stability. However, due to the limited range of applied support pressures available from the TBM data set, limit states could not be fully analyzed. To assure the reliability of a numerical model to determine the actual face stability based on surface settlements during the construction phase, additional research must be done. It is suggested to extend the methods used in this research with physical modelling. For maximum face support pressures, the analytical and numerical models do not coincide. Hydraulic fracturing cannot be modelled in Plaxis 3D. It is recommended not to use numerical modelling to determine the face stability based on settlements at face pressures higher than the face pressures at which an equilibrium is achieved.
...
During the boring of a tunnel in soft soils with a slurry TBM, support pressure is used to achieve equilibrium at the face of the TBM. When this equilibrium is not reached, when the face support pressure is too low or too high, settlements will occur. In this research settlement and pore water pressure measurements are used to monitor the behavior of the soil and estimate the stability of the tunnel face. During boring of the tunnel, the exact stability of the face is not known. The TBM driver has to rely on the provided stratigraphy data, the advised face support pressures range provided by the geotechnical engineers and the experience of the tunnel boring team. Monitoring is not yet used to determine the face stability during construction. To do so, field data from a case study at RijnlandRoute is compared with analytical and numerical models. Sensitivity of the measurement equipment, and of both the analytical (DIN) and numerical model (Plaxis 3D) with respect to soil parameters, are considered. It has been found that the strength parameters of the layer in which the face is located have the highest influence on the minimum face support pressure. For the maximum face support pressure this is the volumetric weight of the entire soil profile above the face. For comparing the (soft soil) field data with numerical results, a Plaxis 3D model is built, and it is determined that HSsmall is a suitable constitutive model to capture the interaction between face stability, tunneling operations and soil behavior. It is shown that the tail void injection influences the settlements above and in front of the cutter head, but this influence is discarded and replaced by a wished in place lining, to simplify the numerical model. A scenario analysis on the sensitivity of soil parameters shows settlements do not vary significantly between the characteristic low and high values. In this analysis correlation of parameters is taken into account. The failure mechanism for the minimum face support pressure coincides with the active cave-in failure mechanism found in literature. For the maximum face support pressure the failure mechanism found in Plaxis 3D does not coincide with the expected hydraulic fracturing failure mode. The continuum representation of the soil in Plaxis 3D does not allow a hydraulic fracturing like failure mechanism to develop. Instead, a blow-out approximately 10 m. in front of the cutterhead occurs. This behaviour better resembles the failure mechanism of a EPB TBM. The field data gathered from the case study shows a thrust wave in front of the cutter head in both settlement and pore water pressure measurements. This thrust wave reaches up to 20 to 40 meters in front of the TBM. The heave induced by the thrust wave reduces the amount of settlements after the TBM passage. Excess pore pressures, induced by a high thrust wave, affect the face stability negatively. The excess pore pressure mainly depends on the advance rate. The higher the advance rate, the less time the pore pressures have to dissipate, leading to an increase in excess pore pressure. The accuracy of the settlements measurement devices is 0.8 mm., and of the spade cells 1.0 kPa. In general, the field data shows settlement curves corresponding to the Peck (1969) Gaussian curve (in lateral and longitudinal direction). Comparing the case study settlements with the numerically generated settlement curves show similar trends. The field data shows lower settlements than the numerical results. This can be due to the presence of excess pore pressures, the accuracy of the TBM data or its interpretation. A method to increase the accuracy, which is expected to result in a better fit with the numerical results, was found in a late phase of the research. This method takes into account the settlements which are induced by the thrust wave in front of the TBM. Comparing the numerical and analytically determined limit support pressures, it is found that the minimum face support pressure are similar in both methods. As similar failure mechanisms are found, numerical modelling seems a reliable way of determining the face stability. However, due to the limited range of applied support pressures available from the TBM data set, limit states could not be fully analyzed. To assure the reliability of a numerical model to determine the actual face stability based on surface settlements during the construction phase, additional research must be done. It is suggested to extend the methods used in this research with physical modelling. For maximum face support pressures, the analytical and numerical models do not coincide. Hydraulic fracturing cannot be modelled in Plaxis 3D. It is recommended not to use numerical modelling to determine the face stability based on settlements at face pressures higher than the face pressures at which an equilibrium is achieved.
Master thesis
(2020)
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Zhenheng Kong, Frans van der Meer, A.C. Akyildiz, Lambertus J. Sluys, Cor Kasbergen
Cardiovascular disease has caused 3.9 million deaths in Europe and over 1.8 million deaths in the European Union, which accounts for 45\% of all deaths in Europe and 37\% of all death in the European Union in 2017. Cardiovascular disease is mainly caused by atherosclerosis. Atherosclerosis is a kind of disease where the inside of the artery gets narrow due to the build-up of plaque. Plaque is an abnormal accumulation of material in the inner layer of the arterial wall. A swelling can be formed by the accumulated material. The swelling may intrude into the channel of the artery wall, which will make the channel get narrower and restrict blood flow. Based on current medical technology, images of the plaques can be taken. However, there are no efficient simulation tools for plaque rupture. In order to set up sufficient simulation tools, a good representation of the material behaviour and the progression of the failure is needed. There are material models for the arterial wall accounting for large deformations (hyperelasticity) and anisotropy in the material response. And, there are also failure models. However, the material models and the failure models have not been combined. In this thesis, three material models and one failure model are included. The three material models are Neo-Hookean material model and two anisotropic models developed for arterial wall tissue developed by Holzapfel and Gasser. They are combined with anisotropic damage model to obtain three new constitutive models for failure of hyperelastic material. After the three constitutive models are set up, a parameter study is performed to explore the material properties of the new constitutive models. Verification of the material models is also included. Finally, the performance of the model is demonstrated with failure analyses on different geometries: a simple plane, a bar, a plane with an imperfection and a plane with a rectangular hole in the middle.
...
Cardiovascular disease has caused 3.9 million deaths in Europe and over 1.8 million deaths in the European Union, which accounts for 45\% of all deaths in Europe and 37\% of all death in the European Union in 2017. Cardiovascular disease is mainly caused by atherosclerosis. Atherosclerosis is a kind of disease where the inside of the artery gets narrow due to the build-up of plaque. Plaque is an abnormal accumulation of material in the inner layer of the arterial wall. A swelling can be formed by the accumulated material. The swelling may intrude into the channel of the artery wall, which will make the channel get narrower and restrict blood flow. Based on current medical technology, images of the plaques can be taken. However, there are no efficient simulation tools for plaque rupture. In order to set up sufficient simulation tools, a good representation of the material behaviour and the progression of the failure is needed. There are material models for the arterial wall accounting for large deformations (hyperelasticity) and anisotropy in the material response. And, there are also failure models. However, the material models and the failure models have not been combined. In this thesis, three material models and one failure model are included. The three material models are Neo-Hookean material model and two anisotropic models developed for arterial wall tissue developed by Holzapfel and Gasser. They are combined with anisotropic damage model to obtain three new constitutive models for failure of hyperelastic material. After the three constitutive models are set up, a parameter study is performed to explore the material properties of the new constitutive models. Verification of the material models is also included. Finally, the performance of the model is demonstrated with failure analyses on different geometries: a simple plane, a bar, a plane with an imperfection and a plane with a rectangular hole in the middle.
Master thesis
(2020)
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Coen Kortendijk, A. Metrikine, E. Lourens, F Besseling, C Jolink, C. Kasbergen
Sandpile behaviour in Mexico Clay soils
Assessing the applicability of sandpiles at the NAICM site as alternative to PVDs
The construction of the new airport of Mexico City (NAICM) is challenging, as the subsoil at the site is very weak. The airport, which is under construction at the moment, is located on top of thick layers of Mexico Clay soils. These clayey layers consist of a mixture of both clay particles and pyroclastic volcanic materials. These unique soils are characterised by a high water content and compressibility. Upon loading, the soft soils will settle as a result of the consolidation process. This consolidation is defined as the dissipation of excess pore water as a result of an increase in stress. The rate of consolidation is governed by the hydraulic conductivity of the soil, which is in general very low in soft soils, and the drainage path. In order to speed up this time consuming process, vertical permeable elements can be installed in the soil. Upon installation of these elements, a reduction in drainage path is realised. This reduction in drainage path allows faster dissipation of excess pore water pressure, hence reducing the consolidation time. Due to the conditions at the site, the design of the runways is challenging. The differential- and residual settlements need to be within strict boundaries in order to keep the runways operational. Prior to the design of the runways, trial embankments have been constructed in order to measure the performance of different soil improvement techniques at this specific site. Based upon this field test results, prefabricated vertical drains (PVDs) were selected as the most efficient soil improvement technique. Besides the PVD trial, the sandpile trial also showed promising results. The PVDs and sandpiles both decrease the drainage path length inside the soft soil layers. The main difference is the relative high stiffness of the sandpiles, the stiffness of the PVDs is negligible. By installing stiff elements in the soft soil, the loads applied on the top of the soils are transferred to deeper and stiffer soils. Hence, the total settlements of the top soft soil layers are reduced. The sandpiles could therefore be feasible alternative to PVDs, applied at locations in which the total settlement needs to be limited.
The investigation into the behaviour of sandpiles in Mexico Clay soils is performed in multiple stages. First, analytical models are used for gaining knowledge about the expected sandpile behaviour. In the second stage the FEM software Plaxis 2D is used for the numerical modelling of the sandpiles, using an axisymmetric model setup. The model is constructed in multiple steps, with increasing complexity. The first models simulate the material behaviour with the Mohr-Coulomb model, in the advanced models the Soft Soil Creep and Hardening Soil models are used. The final numerical model is verified by the measurement data obtained from the field trials.
After fitting the numerical model to the field data, the verified model is used in the sandpile sensitivity analysis. In this analysis the sensitivity of the material properties and geometry of the sandpile on the performance are researched. The residual settlements or performance, which is defined as the difference in settlement after construction and over a period of 8 years, is affected by the length, radius and centre to centre (ctc) distance of the sandpile. Adjusting the pile stiffness has minimal effect on the performance of the sandpile. An optimum in performance is found by varying both the pile radius and ctc distance. A combination of a small pile diameter with a small ctc distance results in the best performance. When comparing the performance of both sandpile and PVD, the PVD is found to be more effective in terms of performance. The additional stiffness of the sandpile is not reducing the total settlements, on the contrary, the self-weight of the piles increases the total settlements by providing an additional load to the soft soil layers located underneath the pile tip. In conclusion the sandpiles have no additional benefit over the use of PVDs, therefore the application of sandpiles at the NAICM site is not a feasible alternative to the use of PVDs. ...
The investigation into the behaviour of sandpiles in Mexico Clay soils is performed in multiple stages. First, analytical models are used for gaining knowledge about the expected sandpile behaviour. In the second stage the FEM software Plaxis 2D is used for the numerical modelling of the sandpiles, using an axisymmetric model setup. The model is constructed in multiple steps, with increasing complexity. The first models simulate the material behaviour with the Mohr-Coulomb model, in the advanced models the Soft Soil Creep and Hardening Soil models are used. The final numerical model is verified by the measurement data obtained from the field trials.
After fitting the numerical model to the field data, the verified model is used in the sandpile sensitivity analysis. In this analysis the sensitivity of the material properties and geometry of the sandpile on the performance are researched. The residual settlements or performance, which is defined as the difference in settlement after construction and over a period of 8 years, is affected by the length, radius and centre to centre (ctc) distance of the sandpile. Adjusting the pile stiffness has minimal effect on the performance of the sandpile. An optimum in performance is found by varying both the pile radius and ctc distance. A combination of a small pile diameter with a small ctc distance results in the best performance. When comparing the performance of both sandpile and PVD, the PVD is found to be more effective in terms of performance. The additional stiffness of the sandpile is not reducing the total settlements, on the contrary, the self-weight of the piles increases the total settlements by providing an additional load to the soft soil layers located underneath the pile tip. In conclusion the sandpiles have no additional benefit over the use of PVDs, therefore the application of sandpiles at the NAICM site is not a feasible alternative to the use of PVDs. ...
The construction of the new airport of Mexico City (NAICM) is challenging, as the subsoil at the site is very weak. The airport, which is under construction at the moment, is located on top of thick layers of Mexico Clay soils. These clayey layers consist of a mixture of both clay particles and pyroclastic volcanic materials. These unique soils are characterised by a high water content and compressibility. Upon loading, the soft soils will settle as a result of the consolidation process. This consolidation is defined as the dissipation of excess pore water as a result of an increase in stress. The rate of consolidation is governed by the hydraulic conductivity of the soil, which is in general very low in soft soils, and the drainage path. In order to speed up this time consuming process, vertical permeable elements can be installed in the soil. Upon installation of these elements, a reduction in drainage path is realised. This reduction in drainage path allows faster dissipation of excess pore water pressure, hence reducing the consolidation time. Due to the conditions at the site, the design of the runways is challenging. The differential- and residual settlements need to be within strict boundaries in order to keep the runways operational. Prior to the design of the runways, trial embankments have been constructed in order to measure the performance of different soil improvement techniques at this specific site. Based upon this field test results, prefabricated vertical drains (PVDs) were selected as the most efficient soil improvement technique. Besides the PVD trial, the sandpile trial also showed promising results. The PVDs and sandpiles both decrease the drainage path length inside the soft soil layers. The main difference is the relative high stiffness of the sandpiles, the stiffness of the PVDs is negligible. By installing stiff elements in the soft soil, the loads applied on the top of the soils are transferred to deeper and stiffer soils. Hence, the total settlements of the top soft soil layers are reduced. The sandpiles could therefore be feasible alternative to PVDs, applied at locations in which the total settlement needs to be limited.
The investigation into the behaviour of sandpiles in Mexico Clay soils is performed in multiple stages. First, analytical models are used for gaining knowledge about the expected sandpile behaviour. In the second stage the FEM software Plaxis 2D is used for the numerical modelling of the sandpiles, using an axisymmetric model setup. The model is constructed in multiple steps, with increasing complexity. The first models simulate the material behaviour with the Mohr-Coulomb model, in the advanced models the Soft Soil Creep and Hardening Soil models are used. The final numerical model is verified by the measurement data obtained from the field trials.
After fitting the numerical model to the field data, the verified model is used in the sandpile sensitivity analysis. In this analysis the sensitivity of the material properties and geometry of the sandpile on the performance are researched. The residual settlements or performance, which is defined as the difference in settlement after construction and over a period of 8 years, is affected by the length, radius and centre to centre (ctc) distance of the sandpile. Adjusting the pile stiffness has minimal effect on the performance of the sandpile. An optimum in performance is found by varying both the pile radius and ctc distance. A combination of a small pile diameter with a small ctc distance results in the best performance. When comparing the performance of both sandpile and PVD, the PVD is found to be more effective in terms of performance. The additional stiffness of the sandpile is not reducing the total settlements, on the contrary, the self-weight of the piles increases the total settlements by providing an additional load to the soft soil layers located underneath the pile tip. In conclusion the sandpiles have no additional benefit over the use of PVDs, therefore the application of sandpiles at the NAICM site is not a feasible alternative to the use of PVDs.
The investigation into the behaviour of sandpiles in Mexico Clay soils is performed in multiple stages. First, analytical models are used for gaining knowledge about the expected sandpile behaviour. In the second stage the FEM software Plaxis 2D is used for the numerical modelling of the sandpiles, using an axisymmetric model setup. The model is constructed in multiple steps, with increasing complexity. The first models simulate the material behaviour with the Mohr-Coulomb model, in the advanced models the Soft Soil Creep and Hardening Soil models are used. The final numerical model is verified by the measurement data obtained from the field trials.
After fitting the numerical model to the field data, the verified model is used in the sandpile sensitivity analysis. In this analysis the sensitivity of the material properties and geometry of the sandpile on the performance are researched. The residual settlements or performance, which is defined as the difference in settlement after construction and over a period of 8 years, is affected by the length, radius and centre to centre (ctc) distance of the sandpile. Adjusting the pile stiffness has minimal effect on the performance of the sandpile. An optimum in performance is found by varying both the pile radius and ctc distance. A combination of a small pile diameter with a small ctc distance results in the best performance. When comparing the performance of both sandpile and PVD, the PVD is found to be more effective in terms of performance. The additional stiffness of the sandpile is not reducing the total settlements, on the contrary, the self-weight of the piles increases the total settlements by providing an additional load to the soft soil layers located underneath the pile tip. In conclusion the sandpiles have no additional benefit over the use of PVDs, therefore the application of sandpiles at the NAICM site is not a feasible alternative to the use of PVDs.