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A.A. Mehrotra
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9 records found
1
Master thesis
(2023)
-
A.P. Joshi, M.A.N. Hendriks, P.A. Korswagen Eguren, A.A. Mehrotra, Okke Bronkhorst, Jelme Pennings
The light and frequent earthquakes in the north of the Netherlands, particularly in the province of Groningen, have recently exposed the unreinforced masonry structures to seismic activities. Since these structures do not adhere to seismic regulations, they are considered vulnerable to seismicity. The ultimate state capacity of the structures is important for an individual's safety, however, these earthquakes are of low intensity and cause aesthetic damage.
In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.
The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.
The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.
The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.
The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation. ...
In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.
The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.
The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.
The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.
The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation. ...
The light and frequent earthquakes in the north of the Netherlands, particularly in the province of Groningen, have recently exposed the unreinforced masonry structures to seismic activities. Since these structures do not adhere to seismic regulations, they are considered vulnerable to seismicity. The ultimate state capacity of the structures is important for an individual's safety, however, these earthquakes are of low intensity and cause aesthetic damage.
In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.
The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.
The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.
The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.
The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation.
In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.
The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.
The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.
The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.
The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation.
Concrete half-joints are a specific support detail in reinforced concrete structures, which reduce the construction height of the total structure. The use of concrete half-joints became popular around 1950s, but decreased its interest as a result of new insights on structural behaviour and collapses of these structures. Typical issues regarding concrete half-joints are either due to inadequate reinforcement detailing or due to deterioration mechanisms. The most critical deterioration is when a crack at the re-entrant corner allows for water ingress and thus corrosion of the rebars. This thesis focuses on the negative influence of this corrosion on the load bearing capacity and proposes an assessment method, which includes the reinforcement detailing. Firstly, problematic half-joints have been categorised and studied for reinforcement detailing. Subsequently, they have been analysed using an analytical tool, in which corrosion was implemented on the rebars. The outcomes were validated numerically.
For this thesis research, a series of Dutch concrete bridges has been studied to identify general reinforcement issues and categorise concrete half-joints. It has been observed that the majority showed short transfer- and/or anchorage lengths of the rebars and that all of them showed no shear stirrups as hanger-reinforcement. In stead, only a horizontal- and hanger rebar are present, which can be accompanied with a diagonal rebar, prestressing at the top or nib (or combinations in between).
An analytical tool is designed to calculate the load bearing capacity of (un)corroded concrete half-joints. The analysis is based on a lower-bound approximation using a strut-and-tie approach and an upper-bound approximation using a kinematic approach. The analytical tool is used to determine the load bearing capacity of the series of investigated Dutch concrete half-joints. Both approximations are comparable when rebar failure is the governing failure mechanism. The strut-and-tie approach also incorporates detailing checks, which are not considered in the kinematic approach. Therefore large differences occur when detailing governs the capacity.
The nodes in the strut-and-tie model, in which two ties are connected to one concrete strut, appear to be critical in the lower-bound solutions. The capacity depends on the concrete strength and dimensions of the node. The dimensions are influenced by the mandrel diameter of the hanger-rebar and anchorage length of the horizontal rebar. In order to study the influence of corrosion on the load bearing capacity, the effect of a reduced rebar capacity due to an increasing corrosion rate was implemented in the analytical tool. The kinematic approach appears to be more sensitive to load bearing capacity loss, as this calculation depends mainly on the strength of the rebars. The strut-and-tie approach is able to redistribute forces over the struts and ties and is less sensitive.
In order to verify the analytical results, a numerical study is performed. The specimens are modelled in such a way that rupture of one of the rebars at the re-entrant corner is governing. Both analytical solutions appear to be conservative compared to the numerical results, in which the lower-bound solutions are very conservative. Different crack’s angles have been found between the upper-bound calculation and numerical results. If the same angle is applied in the analytical tool, the difference reduces from 7% to 2% for an uncorroded concrete half-joint without diagonal. The differences can be explained by the simplification in the kinematic approach, in which the concrete compression zone is not able to transfer shear stresses.
Based on the conclusions of the analytical tool and numerical verification, an assessment method is proposed in which the upper-bound solution is combined with the lower-bound solution. If the load on the concrete half-joint is lower than the calculated lower-bound solution, the concrete half-joint is safe. However, questions arise if the load is between the lower- and upper-bound solution, in which structural safety cannot be guaranteed. The analytical tool is still a useful tool to understand the behaviour and vulnerabilities of the concrete half-joint. The analytical tool is even more useful if the strut-and-tie approach is governed by rupture of the horizontal-, diagonal- or hanger-rebar. The kinematic approach can be extended by implementing the same crack’s angle, which occurs in the existing concrete half-joint.
...
For this thesis research, a series of Dutch concrete bridges has been studied to identify general reinforcement issues and categorise concrete half-joints. It has been observed that the majority showed short transfer- and/or anchorage lengths of the rebars and that all of them showed no shear stirrups as hanger-reinforcement. In stead, only a horizontal- and hanger rebar are present, which can be accompanied with a diagonal rebar, prestressing at the top or nib (or combinations in between).
An analytical tool is designed to calculate the load bearing capacity of (un)corroded concrete half-joints. The analysis is based on a lower-bound approximation using a strut-and-tie approach and an upper-bound approximation using a kinematic approach. The analytical tool is used to determine the load bearing capacity of the series of investigated Dutch concrete half-joints. Both approximations are comparable when rebar failure is the governing failure mechanism. The strut-and-tie approach also incorporates detailing checks, which are not considered in the kinematic approach. Therefore large differences occur when detailing governs the capacity.
The nodes in the strut-and-tie model, in which two ties are connected to one concrete strut, appear to be critical in the lower-bound solutions. The capacity depends on the concrete strength and dimensions of the node. The dimensions are influenced by the mandrel diameter of the hanger-rebar and anchorage length of the horizontal rebar. In order to study the influence of corrosion on the load bearing capacity, the effect of a reduced rebar capacity due to an increasing corrosion rate was implemented in the analytical tool. The kinematic approach appears to be more sensitive to load bearing capacity loss, as this calculation depends mainly on the strength of the rebars. The strut-and-tie approach is able to redistribute forces over the struts and ties and is less sensitive.
In order to verify the analytical results, a numerical study is performed. The specimens are modelled in such a way that rupture of one of the rebars at the re-entrant corner is governing. Both analytical solutions appear to be conservative compared to the numerical results, in which the lower-bound solutions are very conservative. Different crack’s angles have been found between the upper-bound calculation and numerical results. If the same angle is applied in the analytical tool, the difference reduces from 7% to 2% for an uncorroded concrete half-joint without diagonal. The differences can be explained by the simplification in the kinematic approach, in which the concrete compression zone is not able to transfer shear stresses.
Based on the conclusions of the analytical tool and numerical verification, an assessment method is proposed in which the upper-bound solution is combined with the lower-bound solution. If the load on the concrete half-joint is lower than the calculated lower-bound solution, the concrete half-joint is safe. However, questions arise if the load is between the lower- and upper-bound solution, in which structural safety cannot be guaranteed. The analytical tool is still a useful tool to understand the behaviour and vulnerabilities of the concrete half-joint. The analytical tool is even more useful if the strut-and-tie approach is governed by rupture of the horizontal-, diagonal- or hanger-rebar. The kinematic approach can be extended by implementing the same crack’s angle, which occurs in the existing concrete half-joint.
...
Concrete half-joints are a specific support detail in reinforced concrete structures, which reduce the construction height of the total structure. The use of concrete half-joints became popular around 1950s, but decreased its interest as a result of new insights on structural behaviour and collapses of these structures. Typical issues regarding concrete half-joints are either due to inadequate reinforcement detailing or due to deterioration mechanisms. The most critical deterioration is when a crack at the re-entrant corner allows for water ingress and thus corrosion of the rebars. This thesis focuses on the negative influence of this corrosion on the load bearing capacity and proposes an assessment method, which includes the reinforcement detailing. Firstly, problematic half-joints have been categorised and studied for reinforcement detailing. Subsequently, they have been analysed using an analytical tool, in which corrosion was implemented on the rebars. The outcomes were validated numerically.
For this thesis research, a series of Dutch concrete bridges has been studied to identify general reinforcement issues and categorise concrete half-joints. It has been observed that the majority showed short transfer- and/or anchorage lengths of the rebars and that all of them showed no shear stirrups as hanger-reinforcement. In stead, only a horizontal- and hanger rebar are present, which can be accompanied with a diagonal rebar, prestressing at the top or nib (or combinations in between).
An analytical tool is designed to calculate the load bearing capacity of (un)corroded concrete half-joints. The analysis is based on a lower-bound approximation using a strut-and-tie approach and an upper-bound approximation using a kinematic approach. The analytical tool is used to determine the load bearing capacity of the series of investigated Dutch concrete half-joints. Both approximations are comparable when rebar failure is the governing failure mechanism. The strut-and-tie approach also incorporates detailing checks, which are not considered in the kinematic approach. Therefore large differences occur when detailing governs the capacity.
The nodes in the strut-and-tie model, in which two ties are connected to one concrete strut, appear to be critical in the lower-bound solutions. The capacity depends on the concrete strength and dimensions of the node. The dimensions are influenced by the mandrel diameter of the hanger-rebar and anchorage length of the horizontal rebar. In order to study the influence of corrosion on the load bearing capacity, the effect of a reduced rebar capacity due to an increasing corrosion rate was implemented in the analytical tool. The kinematic approach appears to be more sensitive to load bearing capacity loss, as this calculation depends mainly on the strength of the rebars. The strut-and-tie approach is able to redistribute forces over the struts and ties and is less sensitive.
In order to verify the analytical results, a numerical study is performed. The specimens are modelled in such a way that rupture of one of the rebars at the re-entrant corner is governing. Both analytical solutions appear to be conservative compared to the numerical results, in which the lower-bound solutions are very conservative. Different crack’s angles have been found between the upper-bound calculation and numerical results. If the same angle is applied in the analytical tool, the difference reduces from 7% to 2% for an uncorroded concrete half-joint without diagonal. The differences can be explained by the simplification in the kinematic approach, in which the concrete compression zone is not able to transfer shear stresses.
Based on the conclusions of the analytical tool and numerical verification, an assessment method is proposed in which the upper-bound solution is combined with the lower-bound solution. If the load on the concrete half-joint is lower than the calculated lower-bound solution, the concrete half-joint is safe. However, questions arise if the load is between the lower- and upper-bound solution, in which structural safety cannot be guaranteed. The analytical tool is still a useful tool to understand the behaviour and vulnerabilities of the concrete half-joint. The analytical tool is even more useful if the strut-and-tie approach is governed by rupture of the horizontal-, diagonal- or hanger-rebar. The kinematic approach can be extended by implementing the same crack’s angle, which occurs in the existing concrete half-joint.
For this thesis research, a series of Dutch concrete bridges has been studied to identify general reinforcement issues and categorise concrete half-joints. It has been observed that the majority showed short transfer- and/or anchorage lengths of the rebars and that all of them showed no shear stirrups as hanger-reinforcement. In stead, only a horizontal- and hanger rebar are present, which can be accompanied with a diagonal rebar, prestressing at the top or nib (or combinations in between).
An analytical tool is designed to calculate the load bearing capacity of (un)corroded concrete half-joints. The analysis is based on a lower-bound approximation using a strut-and-tie approach and an upper-bound approximation using a kinematic approach. The analytical tool is used to determine the load bearing capacity of the series of investigated Dutch concrete half-joints. Both approximations are comparable when rebar failure is the governing failure mechanism. The strut-and-tie approach also incorporates detailing checks, which are not considered in the kinematic approach. Therefore large differences occur when detailing governs the capacity.
The nodes in the strut-and-tie model, in which two ties are connected to one concrete strut, appear to be critical in the lower-bound solutions. The capacity depends on the concrete strength and dimensions of the node. The dimensions are influenced by the mandrel diameter of the hanger-rebar and anchorage length of the horizontal rebar. In order to study the influence of corrosion on the load bearing capacity, the effect of a reduced rebar capacity due to an increasing corrosion rate was implemented in the analytical tool. The kinematic approach appears to be more sensitive to load bearing capacity loss, as this calculation depends mainly on the strength of the rebars. The strut-and-tie approach is able to redistribute forces over the struts and ties and is less sensitive.
In order to verify the analytical results, a numerical study is performed. The specimens are modelled in such a way that rupture of one of the rebars at the re-entrant corner is governing. Both analytical solutions appear to be conservative compared to the numerical results, in which the lower-bound solutions are very conservative. Different crack’s angles have been found between the upper-bound calculation and numerical results. If the same angle is applied in the analytical tool, the difference reduces from 7% to 2% for an uncorroded concrete half-joint without diagonal. The differences can be explained by the simplification in the kinematic approach, in which the concrete compression zone is not able to transfer shear stresses.
Based on the conclusions of the analytical tool and numerical verification, an assessment method is proposed in which the upper-bound solution is combined with the lower-bound solution. If the load on the concrete half-joint is lower than the calculated lower-bound solution, the concrete half-joint is safe. However, questions arise if the load is between the lower- and upper-bound solution, in which structural safety cannot be guaranteed. The analytical tool is still a useful tool to understand the behaviour and vulnerabilities of the concrete half-joint. The analytical tool is even more useful if the strut-and-tie approach is governed by rupture of the horizontal-, diagonal- or hanger-rebar. The kinematic approach can be extended by implementing the same crack’s angle, which occurs in the existing concrete half-joint.
Structural Utilization of Reclaimed Timber in a Reciprocal Frame Canopy
A Sustainable Design Strategy for the Reuse of Timber
Master thesis
(2022)
-
C. Haasis, H.R. Schipper, A.A. Mehrotra, C. Noteboom, M. Mirra, Olga Popovic Larsen, Xan Browne
The buildings construction industry is demanded to reduce its ecological footprint to mitigate its contribution to climate change. In this context, a novel sustainable design strategy for the reuse of timber was developed in this Master thesis. The design strategy focuses on the utilization of the material “reclaimed timber” (RT) in the structural system “reciprocal frame” (RF). RT is timber which is harvested from the load bearing structure of dismantled buildings. Large quantities of RT are currently fixed in the building stock. RFs are a family of structures that boast with a rich variety of forms and diverse functions. The utilization of RT in RFs is favorable because RT items which are relatively short can span distances longer than their length when combined with RFs.
To inform the development of the design strategy a literature review on both RT and RFs was conducted. These theoretical studies were supplemented with more practical methods of investigation: RT was inspected first-hand during a visit of a salvage yard that stores RT. Throughout the project physical modeling was used as tool to explore and illustrate the characteristics of RFs. Moreover, during a three-day workshop in which a RF canopy structure from RT was built, important design aspects of RFs were investigated. This first part of the research concluded with describing the state-of-the art of the structural utilization of RT and providing a comprehensive overview of the structural design with RFs.
Key findings of the theoretical and practical studies on both RT and RFs were that the limited stock of available RT items and the geometric complexity of RFs are the two major problems when designing a RF with RT. To solve the two problems a novel RT database configuration that archives the properties of specific RT items was developed. This RT database was applied in conjunction with a novel bottom-up geometry generation model for Rainbow RFs. The Rainbow RF was identified as advantageous for the combination with RT. It can be used to generate expressive spatial assemblies with a relatively low geometric complexity and a high degree of regularity. From a structural perspective the Rainbow RF has the benefit of efficiently transferring axial forces, which reduces the bending action that is typical for RF. Moreover, it achieves flexural rigidity without using expensive moment resistant joints.
The key findings were integrated to form a preliminary design strategy. In a case study the preliminary strategy was used to design a RT RF for a railway station canopy that spans an area of 14.0 m x 27.0 m. The RT stock of the case study was defined by a database that is comprised of 30 stacks of RT items. Based on the material stock 118 geometric design proposals were generated using the bottom-up model. Three of the proposals were developed into safe structural designs. The three safe structural designs demonstrate that the RT items compensate their low strength grade with their relatively large cross-sections.
Based on a discussion of the case study’s design process, a complete design strategy for the structural utilization of RT in RF structures is derived. In the first design phase the shape of the building and the flow of forces through the structure are established. The material stock is defined using the novel RT database configuration. For each RT stack multiple geometric design proposals are developed with the bottom-up model in design phase 3. The bottom-up model is set up in “Grasshopper 3D” and “Python”. For the fourth phase, a versatile algorithm is programmed that automates the structural design to a large degree. This enables to assess many geometric design proposals with considerable accuracy in a short time. The Structural Design concludes with a complete design of the RF structure. The structural design algorithm is also programmed in Grasshopper 3D and Python, the plug-in “Karamba3D” is used for finite-element analyses. The Detail Design rounds the design strategy off by detailing the structure’s joints.
...
To inform the development of the design strategy a literature review on both RT and RFs was conducted. These theoretical studies were supplemented with more practical methods of investigation: RT was inspected first-hand during a visit of a salvage yard that stores RT. Throughout the project physical modeling was used as tool to explore and illustrate the characteristics of RFs. Moreover, during a three-day workshop in which a RF canopy structure from RT was built, important design aspects of RFs were investigated. This first part of the research concluded with describing the state-of-the art of the structural utilization of RT and providing a comprehensive overview of the structural design with RFs.
Key findings of the theoretical and practical studies on both RT and RFs were that the limited stock of available RT items and the geometric complexity of RFs are the two major problems when designing a RF with RT. To solve the two problems a novel RT database configuration that archives the properties of specific RT items was developed. This RT database was applied in conjunction with a novel bottom-up geometry generation model for Rainbow RFs. The Rainbow RF was identified as advantageous for the combination with RT. It can be used to generate expressive spatial assemblies with a relatively low geometric complexity and a high degree of regularity. From a structural perspective the Rainbow RF has the benefit of efficiently transferring axial forces, which reduces the bending action that is typical for RF. Moreover, it achieves flexural rigidity without using expensive moment resistant joints.
The key findings were integrated to form a preliminary design strategy. In a case study the preliminary strategy was used to design a RT RF for a railway station canopy that spans an area of 14.0 m x 27.0 m. The RT stock of the case study was defined by a database that is comprised of 30 stacks of RT items. Based on the material stock 118 geometric design proposals were generated using the bottom-up model. Three of the proposals were developed into safe structural designs. The three safe structural designs demonstrate that the RT items compensate their low strength grade with their relatively large cross-sections.
Based on a discussion of the case study’s design process, a complete design strategy for the structural utilization of RT in RF structures is derived. In the first design phase the shape of the building and the flow of forces through the structure are established. The material stock is defined using the novel RT database configuration. For each RT stack multiple geometric design proposals are developed with the bottom-up model in design phase 3. The bottom-up model is set up in “Grasshopper 3D” and “Python”. For the fourth phase, a versatile algorithm is programmed that automates the structural design to a large degree. This enables to assess many geometric design proposals with considerable accuracy in a short time. The Structural Design concludes with a complete design of the RF structure. The structural design algorithm is also programmed in Grasshopper 3D and Python, the plug-in “Karamba3D” is used for finite-element analyses. The Detail Design rounds the design strategy off by detailing the structure’s joints.
...
The buildings construction industry is demanded to reduce its ecological footprint to mitigate its contribution to climate change. In this context, a novel sustainable design strategy for the reuse of timber was developed in this Master thesis. The design strategy focuses on the utilization of the material “reclaimed timber” (RT) in the structural system “reciprocal frame” (RF). RT is timber which is harvested from the load bearing structure of dismantled buildings. Large quantities of RT are currently fixed in the building stock. RFs are a family of structures that boast with a rich variety of forms and diverse functions. The utilization of RT in RFs is favorable because RT items which are relatively short can span distances longer than their length when combined with RFs.
To inform the development of the design strategy a literature review on both RT and RFs was conducted. These theoretical studies were supplemented with more practical methods of investigation: RT was inspected first-hand during a visit of a salvage yard that stores RT. Throughout the project physical modeling was used as tool to explore and illustrate the characteristics of RFs. Moreover, during a three-day workshop in which a RF canopy structure from RT was built, important design aspects of RFs were investigated. This first part of the research concluded with describing the state-of-the art of the structural utilization of RT and providing a comprehensive overview of the structural design with RFs.
Key findings of the theoretical and practical studies on both RT and RFs were that the limited stock of available RT items and the geometric complexity of RFs are the two major problems when designing a RF with RT. To solve the two problems a novel RT database configuration that archives the properties of specific RT items was developed. This RT database was applied in conjunction with a novel bottom-up geometry generation model for Rainbow RFs. The Rainbow RF was identified as advantageous for the combination with RT. It can be used to generate expressive spatial assemblies with a relatively low geometric complexity and a high degree of regularity. From a structural perspective the Rainbow RF has the benefit of efficiently transferring axial forces, which reduces the bending action that is typical for RF. Moreover, it achieves flexural rigidity without using expensive moment resistant joints.
The key findings were integrated to form a preliminary design strategy. In a case study the preliminary strategy was used to design a RT RF for a railway station canopy that spans an area of 14.0 m x 27.0 m. The RT stock of the case study was defined by a database that is comprised of 30 stacks of RT items. Based on the material stock 118 geometric design proposals were generated using the bottom-up model. Three of the proposals were developed into safe structural designs. The three safe structural designs demonstrate that the RT items compensate their low strength grade with their relatively large cross-sections.
Based on a discussion of the case study’s design process, a complete design strategy for the structural utilization of RT in RF structures is derived. In the first design phase the shape of the building and the flow of forces through the structure are established. The material stock is defined using the novel RT database configuration. For each RT stack multiple geometric design proposals are developed with the bottom-up model in design phase 3. The bottom-up model is set up in “Grasshopper 3D” and “Python”. For the fourth phase, a versatile algorithm is programmed that automates the structural design to a large degree. This enables to assess many geometric design proposals with considerable accuracy in a short time. The Structural Design concludes with a complete design of the RF structure. The structural design algorithm is also programmed in Grasshopper 3D and Python, the plug-in “Karamba3D” is used for finite-element analyses. The Detail Design rounds the design strategy off by detailing the structure’s joints.
To inform the development of the design strategy a literature review on both RT and RFs was conducted. These theoretical studies were supplemented with more practical methods of investigation: RT was inspected first-hand during a visit of a salvage yard that stores RT. Throughout the project physical modeling was used as tool to explore and illustrate the characteristics of RFs. Moreover, during a three-day workshop in which a RF canopy structure from RT was built, important design aspects of RFs were investigated. This first part of the research concluded with describing the state-of-the art of the structural utilization of RT and providing a comprehensive overview of the structural design with RFs.
Key findings of the theoretical and practical studies on both RT and RFs were that the limited stock of available RT items and the geometric complexity of RFs are the two major problems when designing a RF with RT. To solve the two problems a novel RT database configuration that archives the properties of specific RT items was developed. This RT database was applied in conjunction with a novel bottom-up geometry generation model for Rainbow RFs. The Rainbow RF was identified as advantageous for the combination with RT. It can be used to generate expressive spatial assemblies with a relatively low geometric complexity and a high degree of regularity. From a structural perspective the Rainbow RF has the benefit of efficiently transferring axial forces, which reduces the bending action that is typical for RF. Moreover, it achieves flexural rigidity without using expensive moment resistant joints.
The key findings were integrated to form a preliminary design strategy. In a case study the preliminary strategy was used to design a RT RF for a railway station canopy that spans an area of 14.0 m x 27.0 m. The RT stock of the case study was defined by a database that is comprised of 30 stacks of RT items. Based on the material stock 118 geometric design proposals were generated using the bottom-up model. Three of the proposals were developed into safe structural designs. The three safe structural designs demonstrate that the RT items compensate their low strength grade with their relatively large cross-sections.
Based on a discussion of the case study’s design process, a complete design strategy for the structural utilization of RT in RF structures is derived. In the first design phase the shape of the building and the flow of forces through the structure are established. The material stock is defined using the novel RT database configuration. For each RT stack multiple geometric design proposals are developed with the bottom-up model in design phase 3. The bottom-up model is set up in “Grasshopper 3D” and “Python”. For the fourth phase, a versatile algorithm is programmed that automates the structural design to a large degree. This enables to assess many geometric design proposals with considerable accuracy in a short time. The Structural Design concludes with a complete design of the RF structure. The structural design algorithm is also programmed in Grasshopper 3D and Python, the plug-in “Karamba3D” is used for finite-element analyses. The Detail Design rounds the design strategy off by detailing the structure’s joints.
Design and optimization of FRP traffic decks considering uplift bolt forces
Based on analytical and numerical approaches
Master thesis
(2022)
-
L. Molenaar, M. Pavlovic, A. Christoforidou, A.A. Mehrotra, R. Grefhorst, T. Sharma
This research is about which geometry of FRP slabs is the most optimal, in terms of costs, to use for a given load and boundary conditions taking the occurring uplift bolt forces into account. The first part of the report focuses on the calculation of the uplift forces in the bolted connections caused by the moving loads. For this, first a detailed numerical model is made in Abaqus. Based on this most detailed numerical model, different simplifications are made to make the calculations easier and less time-consuming. Numerical models with linear bolts instead of non-linear bolts and with load superposition using a one-wheel load instead of a complete vehicle are considered. Next to this, equivalent material properties are calculated to make a model with an orthotropic deck plate instead of modeled geometry of skins and webs. For the numerical model with this orthotropic deck, the same simplifications are applied. Next to the numerical models, different analytical beam and plate models are considered. All different numerical and analytical models made, are compared on possibilities, calculation and modeling time and accuracy. Based on the comparison between the models and the capacity of the connections, it is concluded that the uplift design of the bolted connections does not need to be taken into account in the optimization of the slabs.
The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.
Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.
...
The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.
Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.
...
This research is about which geometry of FRP slabs is the most optimal, in terms of costs, to use for a given load and boundary conditions taking the occurring uplift bolt forces into account. The first part of the report focuses on the calculation of the uplift forces in the bolted connections caused by the moving loads. For this, first a detailed numerical model is made in Abaqus. Based on this most detailed numerical model, different simplifications are made to make the calculations easier and less time-consuming. Numerical models with linear bolts instead of non-linear bolts and with load superposition using a one-wheel load instead of a complete vehicle are considered. Next to this, equivalent material properties are calculated to make a model with an orthotropic deck plate instead of modeled geometry of skins and webs. For the numerical model with this orthotropic deck, the same simplifications are applied. Next to the numerical models, different analytical beam and plate models are considered. All different numerical and analytical models made, are compared on possibilities, calculation and modeling time and accuracy. Based on the comparison between the models and the capacity of the connections, it is concluded that the uplift design of the bolted connections does not need to be taken into account in the optimization of the slabs.
The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.
Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.
The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.
Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.
With the advent of Computer-Aided Design, the design and fabrication of complex free-form shells have become easier to achieve. However, this results in extensive usage of custom-made formworks for the production of shell components and falseworks which provide support for the shell during the construction process. Therefore, a modular design method is proposed for generating form-active spatial structures out of stackable blocks of a few types, having in mind its potential applications such as housing. Instead of shells, spatial masonry structures are thus the main consideration in the design process considering building on top of a vaulted ceiling. By designing a 3D interlocking grid and introducing a four-step topological design that is coupled with structural verification processes based on finite element modelling and discrete element modelling simulations, the geometry of interlocking stackable modular blocks can be automatically generated for constructing such spatial masonry structures. The proposed method ensures that the designed vaults are modular, reconfigurable, and self-supporting during construction, thus increasing the efficiency of mass production while allowing for combinatorial mass customization in designs.
...
With the advent of Computer-Aided Design, the design and fabrication of complex free-form shells have become easier to achieve. However, this results in extensive usage of custom-made formworks for the production of shell components and falseworks which provide support for the shell during the construction process. Therefore, a modular design method is proposed for generating form-active spatial structures out of stackable blocks of a few types, having in mind its potential applications such as housing. Instead of shells, spatial masonry structures are thus the main consideration in the design process considering building on top of a vaulted ceiling. By designing a 3D interlocking grid and introducing a four-step topological design that is coupled with structural verification processes based on finite element modelling and discrete element modelling simulations, the geometry of interlocking stackable modular blocks can be automatically generated for constructing such spatial masonry structures. The proposed method ensures that the designed vaults are modular, reconfigurable, and self-supporting during construction, thus increasing the efficiency of mass production while allowing for combinatorial mass customization in designs.
For the renovation of the Suurhoff bridge, Arup decided to design and propose a new, innovative strengthening scheme, which improves the fatigue performance of the bridge deck and extends the design life of the bridge by at least 15 years. In this strengthening scheme, a steel plate is placed on top of the existing deck plate with a layer of epoxy in between. Preloaded injection bolts are also used to connect the strengthening plate with the deck plate. This strengthening techniques has clear advantages over the current alternatives with regard to weight, execution time, risks and flexibility in the design.
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.
...
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.
...
For the renovation of the Suurhoff bridge, Arup decided to design and propose a new, innovative strengthening scheme, which improves the fatigue performance of the bridge deck and extends the design life of the bridge by at least 15 years. In this strengthening scheme, a steel plate is placed on top of the existing deck plate with a layer of epoxy in between. Preloaded injection bolts are also used to connect the strengthening plate with the deck plate. This strengthening techniques has clear advantages over the current alternatives with regard to weight, execution time, risks and flexibility in the design.
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.
Master thesis
(2022)
-
R.P. Brouwers, Giorgia Giardina, Max Hendriks, Dominika Malinowska, Pietro Milillo, Anjali Mehrotra
Structural health monitoring of buildings is useful for a few reasons. It provides information on the usage and cause of damage to a building. This can result in targeted maintenance or allow for potential improvements.
Traditionally, a building can be monitored by installing sensors during construction or maintenance work. These can be strain gauges, inertial measurement units or surveying equipment. However, not all buildings have such sensors installed due to lack of space or the cost of the equipment. To overcome this, a spaceborne technique shows potential, namely multi-temporal interferometric synthetic aperture radar (MT-InSAR). This technique has already been applied to monitor damage to sections of buildings or large structures, for instance facades or deformations of bridges. In the context of entire buildings, the result of an MT-InSAR analysis has not yet been paired with a computational model. This is mainly due to the relatively small scale of a building and low spatial density of the displacement data.
This thesis integrates remote sensing data, acquiring displacements due to mining, with a computational structural finite element model of a church structure. The displacements have been interpolated using MT-InSAR data, which contains projections of nonlinear displacements in vertical and West-East directions. The interpolation has been performed using two techniques. The first is Ordinary Kriging, which is used to obtain a general insight into the deformations and the shape of the deformed region near the church. The second uses the least squares method to fit polynomial shape functions. The resulting displacements of the least squares analysis have been integrated into a nonlinear structural finite element model. The structural model consists of a soil-structure interaction model and nonlinear material properties, and is used to assess crack propagation.
Integrating remote sensing with computational modelling, shows potential in providing a monitoring technique for buildings. The interpolation method can be used to obtain displacements at a building, even when the spatial density of the InSAR analysis is limited. The main limitation is the information on the horizontal displacements obtained by the InSAR technique, where the displacement along the North-South is unknown. Furthermore, the structure and integration can then be performed using a finite element model, which can follow crack propagation and account for soil-structure interaction. ...
Traditionally, a building can be monitored by installing sensors during construction or maintenance work. These can be strain gauges, inertial measurement units or surveying equipment. However, not all buildings have such sensors installed due to lack of space or the cost of the equipment. To overcome this, a spaceborne technique shows potential, namely multi-temporal interferometric synthetic aperture radar (MT-InSAR). This technique has already been applied to monitor damage to sections of buildings or large structures, for instance facades or deformations of bridges. In the context of entire buildings, the result of an MT-InSAR analysis has not yet been paired with a computational model. This is mainly due to the relatively small scale of a building and low spatial density of the displacement data.
This thesis integrates remote sensing data, acquiring displacements due to mining, with a computational structural finite element model of a church structure. The displacements have been interpolated using MT-InSAR data, which contains projections of nonlinear displacements in vertical and West-East directions. The interpolation has been performed using two techniques. The first is Ordinary Kriging, which is used to obtain a general insight into the deformations and the shape of the deformed region near the church. The second uses the least squares method to fit polynomial shape functions. The resulting displacements of the least squares analysis have been integrated into a nonlinear structural finite element model. The structural model consists of a soil-structure interaction model and nonlinear material properties, and is used to assess crack propagation.
Integrating remote sensing with computational modelling, shows potential in providing a monitoring technique for buildings. The interpolation method can be used to obtain displacements at a building, even when the spatial density of the InSAR analysis is limited. The main limitation is the information on the horizontal displacements obtained by the InSAR technique, where the displacement along the North-South is unknown. Furthermore, the structure and integration can then be performed using a finite element model, which can follow crack propagation and account for soil-structure interaction. ...
Structural health monitoring of buildings is useful for a few reasons. It provides information on the usage and cause of damage to a building. This can result in targeted maintenance or allow for potential improvements.
Traditionally, a building can be monitored by installing sensors during construction or maintenance work. These can be strain gauges, inertial measurement units or surveying equipment. However, not all buildings have such sensors installed due to lack of space or the cost of the equipment. To overcome this, a spaceborne technique shows potential, namely multi-temporal interferometric synthetic aperture radar (MT-InSAR). This technique has already been applied to monitor damage to sections of buildings or large structures, for instance facades or deformations of bridges. In the context of entire buildings, the result of an MT-InSAR analysis has not yet been paired with a computational model. This is mainly due to the relatively small scale of a building and low spatial density of the displacement data.
This thesis integrates remote sensing data, acquiring displacements due to mining, with a computational structural finite element model of a church structure. The displacements have been interpolated using MT-InSAR data, which contains projections of nonlinear displacements in vertical and West-East directions. The interpolation has been performed using two techniques. The first is Ordinary Kriging, which is used to obtain a general insight into the deformations and the shape of the deformed region near the church. The second uses the least squares method to fit polynomial shape functions. The resulting displacements of the least squares analysis have been integrated into a nonlinear structural finite element model. The structural model consists of a soil-structure interaction model and nonlinear material properties, and is used to assess crack propagation.
Integrating remote sensing with computational modelling, shows potential in providing a monitoring technique for buildings. The interpolation method can be used to obtain displacements at a building, even when the spatial density of the InSAR analysis is limited. The main limitation is the information on the horizontal displacements obtained by the InSAR technique, where the displacement along the North-South is unknown. Furthermore, the structure and integration can then be performed using a finite element model, which can follow crack propagation and account for soil-structure interaction.
Traditionally, a building can be monitored by installing sensors during construction or maintenance work. These can be strain gauges, inertial measurement units or surveying equipment. However, not all buildings have such sensors installed due to lack of space or the cost of the equipment. To overcome this, a spaceborne technique shows potential, namely multi-temporal interferometric synthetic aperture radar (MT-InSAR). This technique has already been applied to monitor damage to sections of buildings or large structures, for instance facades or deformations of bridges. In the context of entire buildings, the result of an MT-InSAR analysis has not yet been paired with a computational model. This is mainly due to the relatively small scale of a building and low spatial density of the displacement data.
This thesis integrates remote sensing data, acquiring displacements due to mining, with a computational structural finite element model of a church structure. The displacements have been interpolated using MT-InSAR data, which contains projections of nonlinear displacements in vertical and West-East directions. The interpolation has been performed using two techniques. The first is Ordinary Kriging, which is used to obtain a general insight into the deformations and the shape of the deformed region near the church. The second uses the least squares method to fit polynomial shape functions. The resulting displacements of the least squares analysis have been integrated into a nonlinear structural finite element model. The structural model consists of a soil-structure interaction model and nonlinear material properties, and is used to assess crack propagation.
Integrating remote sensing with computational modelling, shows potential in providing a monitoring technique for buildings. The interpolation method can be used to obtain displacements at a building, even when the spatial density of the InSAR analysis is limited. The main limitation is the information on the horizontal displacements obtained by the InSAR technique, where the displacement along the North-South is unknown. Furthermore, the structure and integration can then be performed using a finite element model, which can follow crack propagation and account for soil-structure interaction.
From least-weight to least-environmental-impacting truss structures
A method to minimize the total environmental cost with the Ground Structure Method for the welding, coating and construction material
Climate change is changing the world. Where previously efficient use of materials was mainly applied to realize cost savings, this can also help to reduce the footprint of a construction. There is a rather direct and obvious relationship between the amount of material required in a construction and its environmental impact. Of course, the environmental impact is not solely dependent on this metric, but minimizing the weight of the structure is a great starting point. This thesis focusses on minimizing the environmental impact of a welded truss bridge. In addition to the required volume of construction material, the environmental costs for the welding and conservation are also taken into account. A case study is performed on a bicycle bridge crossing a highway that is built in the Netherlands.
The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:
Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?
The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).
This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.
All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.
...
The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:
Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?
The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).
This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.
All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.
...
Climate change is changing the world. Where previously efficient use of materials was mainly applied to realize cost savings, this can also help to reduce the footprint of a construction. There is a rather direct and obvious relationship between the amount of material required in a construction and its environmental impact. Of course, the environmental impact is not solely dependent on this metric, but minimizing the weight of the structure is a great starting point. This thesis focusses on minimizing the environmental impact of a welded truss bridge. In addition to the required volume of construction material, the environmental costs for the welding and conservation are also taken into account. A case study is performed on a bicycle bridge crossing a highway that is built in the Netherlands.
The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:
Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?
The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).
This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.
All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.
The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:
Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?
The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).
This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.
All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.
Analyzing reconstruction scenarios for dolmen D14 using non-destructive, digital methods
With a focus on the dislocated capstone
Master thesis
(2021)
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E.L. Theuws, D.J.M. Ngan-Tillard, L. Truong, A.A. Mehrotra, R.C. Lindenbergh, G. Giardina
The lack of insight regarding the stability of many dolmen in the Netherlands is problematic. In 2019, a capstone fell down dolmen D14, greatly damaging this cultural heritage. In order to decide on whether it would be wise to reconstruct this dolmen, it is useful to understand the stability of potential reconstruction scenarios without having to perform invasive tests that could damage the structure. To this end, this research has focused on the application of non-destructive, digital methods to analyze the stability of dolmen D14. Laser scanners were used to obtain point cloud data from the zone around the dislocated capstone, with which 3D meshes were created. Furthermore, tests were conducted to estimate the relevant parameters to quantify the shear strength of the rock contact areas. This was done in the field using the Equotip and Barton’s comb and by performing tilt tests and Golder shear box tests in the laboratory. For the rock parameters, a basic friction angle of 33° was found with tilt tests and a residual friction angle of 31.2° and 30.5° was found for the Golder shear box on a flat sample. The meshes and rock parameters were used as input to conduct stability analyses in 3DEC. Two different models were analyzed, one based on the rock configuration as it was in 2019 (Model 1) and the second model with a rock configuration as it was in 1925 (Model 2). In the stability analysis, it was found that Model 1 is much more unstable compared to Model 2. The minimum pushing force for instability of the structure was 2 kN for Model 1 and 94 kN for Model 2, for the conditions under research. Furthermore, it was found that the number of cycles used in the analysis, mesh coarseness and rock joint friction angle all have a significant impact on the model results. All in all, this research has demonstrated the potential for using digital and non-destructive methods to analyze the stability of megalithic structures.
...
The lack of insight regarding the stability of many dolmen in the Netherlands is problematic. In 2019, a capstone fell down dolmen D14, greatly damaging this cultural heritage. In order to decide on whether it would be wise to reconstruct this dolmen, it is useful to understand the stability of potential reconstruction scenarios without having to perform invasive tests that could damage the structure. To this end, this research has focused on the application of non-destructive, digital methods to analyze the stability of dolmen D14. Laser scanners were used to obtain point cloud data from the zone around the dislocated capstone, with which 3D meshes were created. Furthermore, tests were conducted to estimate the relevant parameters to quantify the shear strength of the rock contact areas. This was done in the field using the Equotip and Barton’s comb and by performing tilt tests and Golder shear box tests in the laboratory. For the rock parameters, a basic friction angle of 33° was found with tilt tests and a residual friction angle of 31.2° and 30.5° was found for the Golder shear box on a flat sample. The meshes and rock parameters were used as input to conduct stability analyses in 3DEC. Two different models were analyzed, one based on the rock configuration as it was in 2019 (Model 1) and the second model with a rock configuration as it was in 1925 (Model 2). In the stability analysis, it was found that Model 1 is much more unstable compared to Model 2. The minimum pushing force for instability of the structure was 2 kN for Model 1 and 94 kN for Model 2, for the conditions under research. Furthermore, it was found that the number of cycles used in the analysis, mesh coarseness and rock joint friction angle all have a significant impact on the model results. All in all, this research has demonstrated the potential for using digital and non-destructive methods to analyze the stability of megalithic structures.