Engineering firm Pieters Bouwtechniek Delft has designed many cantilevering elements in Compact Reinforced Composite over the past years. This material, often abbreviated as CRC, is an UHPFRC developed by Hi-Con Denmark and the material distinguishes itself from other concretes as it incorporates large volumes of steel fibres and reinforcement steel. As a result it is a ductile concrete type with outstanding crack controlling properties. One of the challenges met during designing with CRC is the fact that the Eurocode does not implement the improved properties of the material, such as the improved post-cracking response which is a result of the addition of fibres. This results in designs often requiring stirrups in order to comply with the Eurocode with regard to the shear capacity and the prevention of brittle failure.An example case where this problem was faced, is in the design of the landing platform in a staircase for the Raqtan project, engineered by Pieters Bouwtechniek. This design consist of a cantilevered platform, connected to a wall via a console. The Eurocode requires the addition of stirrups, while it is expected that these stirrups are not required in order to provide a sufficiently safe design. Therefore the following question was raised: Were stirrups required in the console in the design of the Raqtan landing platform in order to obtain a level of safety as required by the Eurocode? This report researched the structural response of the element without the application of stirrups in order to answer this question and determine whether the safety standards as stated in the Eurocode are met. The design without the stirrups is validated in three ways. The first method is by application of multiple design standards which incorporate a contribution by the fibres, such as the Model Code 2010 and the renewed French annex to the Eurocode. Most codes did not validate the design and predicted shear failure before the design load was reached. The French annex did validate the application of the design without stirrups. This is a result of the underlying principles used for this approach: the French guideline bases the tensile behaviour of the UHPFRC on the uni-axial tensile curve, while the other guidelines are based on the flexural tensile curve.The second validation method was through the Finite Element Method. Multiple tensile models were validated against previous experiments and were then used to determine the structural response and ultimate capacity of the Raqtan element. The models failed in bending at a capacity above the design load, thus validating the design. After the results were analytically validated, a variation study was performed on the influence of certain model properties on the structural response. The variations, such as the boundary conditions and mesh configuration, did not significantly influence the ultimate capacity. This analysis validated the application of the design without stirrups. The third and last validation was performed by testing multiple elements in the lab to find the actual capacity. Both elements without and with stirrups were tested to compare the resulting change in structural response. Some elements were reinforced to increase the bending capacity by at least 50%, as the FE models predicted failure in bending even when mean material properties were applied. The reinforced elements did not fail in shear as well, which demonstrated that the bending moment capacity was not only governing, but also significantly lower than the shear capacity. The derived design values for the ultimate load resulted in sufficient capacity for the element to resist the design loads.Combining the performed validations, it is concluded that the element's shear capacity was not governing for the ultimate resistance as it was at least 50% higher than the found the bending moment capacity. This bending moment capacity was sufficient according to all applied codes. When this capacity is taken as the total capacity of the element, it can be stated that the element complies with the codes and therefore provides a level of safety as required by the Eurocode. ... Read more

In the Netherlands, a lot of traffic congestion occurs on motorways. This problem is most severe nearby larger cities. Utrecht is one of these cities. To improve traffic flow in this area, a huge masterplan is designed by Rijkswaterstaat called “A27/A12 Ring Utrecht”. One part of this masterplan consists of the motorway A27 at Amelisweerd. Here, the A27 is situated in a U-shaped concrete structure and must be expanded at both sides. Across the motorway a deck structure is going to be constructed with on top a public garden. This structure spans the total width of the A27 for 249 meters and is called The Green Connection.
According to the original design of Rijkswaterstaat, this deck structure should be realized with an intermediate support. It will be advantageous to omit this structure, since it has a complex execution method. Therefore, it’s investigated if The Green Connection can be realized without the use of an intermediate support.
Then, the execution aspects of the original design will be discussed more thoroughly. The first challenge is constructing the extended parts which is explicated according to 11 main tasks. These tasks seem to be relatively straightforward to execute. After realizing the extended parts, an intermediate support must be constructed. It is found that the existing foundation lacks bearing capacity by far. A new strengthened strip foundation with extra foundation piles must be realised in the middle of the motorway. Due to the boundary conditions (such as the water pressure beneath the structure and permanent drainage is prohibited), the only possibility left is to construct small building pits, compartments, within the existing structure. Such a compartment has a rough length of about 20 meters, will be about 6.5 meters wide and must be constructed 13 times.
Thereafter, the deck structure should be assembled. Three alternatives in methods of assembly are outlined and discussed with the help of the same key-words. All three methods could be realized. But, it’s important to indicate that with some extra investments, the remaining space for traffic could be maximized during assembly.
After discussing the execution aspects of the original design, the technical feasibility of the single span deck structure was investigated more thoroughly. In the Preliminary Study was deduced that two structural designs seem to be a possible solution in constructing The Green Connection. It turned out that the box beam design seems to be advantageous. Although this judgement is substantiated with preliminary calculations and an overall execution plan, it still required more research. Therefore, a reliable structural design is performed for a 75-meter span beam which can be used as a single span deck structure. It does exceed the boundary condition of 280 tons which was posed initially with 8%. However, no optimizations have been applied to this design. If the enumerated optimizations are performed, a beam can be designed according the boundary condition and possibly even less.
When the original design of Rijkswaterstaat is compared to the single span design, the differences are quite straightforward. In essence, the question arises whether the extra money of constructing a single span deck structure outweigh the money which can be saved by leaving out the intermediate support and constructing the extended parts 25% narrower.
Rijkswaterstaat has performed a design with an intermediate support. In this thesis, the feasibility of this design is investigated, and in particular this support. The only possible method of execution in realizing the support is upon condition that a temporary applied drainage system will be feasible and approved by the authority. When the authority states that draining ground water is prohibited, the original design isn’t feasible anymore. In that case, the single span design isn’t just an alternative to the original design, but is the only feasible solution.
Concludingly, providing the applied principles of this thesis, it is strongly recommended against constructing an intermediate support within the existing U-shaped concrete structure. Since the structural reliability of a 75-meter span beam is proven, an intermediate support wall is redundant. Therefore, the single span design is less risky, less time consuming and less expensive compared to the original design. ... Read more

The growing need for strengthening of concrete structures to improve their structural performance challenges structural engineers to come up with strengthening techniques that is most suitable and effective for a structural system in its deteriorated state. Although there are quite a few techniques in practice for strengthening of concrete structures -reinforced or prestressed, various factors limit their efficiency and performance. Use of novel concrete-based materials such as Ultra High Performance Fibre Reinforced Composite (UHPFRC) can lead to an effective strengthening system due to the exceptional material properties of UHPFRC. In particular, the strain hardening behavior of UHPFRC in tension and its excellent durability. Out of the two main mechanisms of failure in concrete elements namely flexure failure and shear failure, shear failure is the most critical due to the abrupt nature of its mechanisms that leads to complete collapse of the structures with no sign of warning. This makes shear strengthening of prestressed concrete structures, that typically form the supporting elements in large infrastructural units such as bridges, a very essential course of action. To investigate the effectiveness of using UHPFRC in shear strengthening of prestressed concrete elements, the post-tensioned T girders of Helperzoom bridge, Groningen, Netherlands are chosen as reference beams which are strengthened with UHPFRC. The reference beams are subjected to a 3-point bending test to determine their failure mechanism and structural capacity. The reference beam is modelled, and tests are simulated by finite element analysis using ATENA. Since the simulated beam failure in shear compression rather than shear tension by localization of the shear tension crack. In order to understand this behavior and the failure mechanism and to check if the results from the simulations are reasonable, a detailed analysis is performed. The influence of shear reinforcement and prestressing, active in the critical shear region, on the shear capacity and the final failure mode are investigated. The results from the numerical analysis are compared to the results from experimental shear tests performed on existing post-tensioned girders which exhibit a similar mode of failure as observed in the reference T beams. The shear capacity of the reference T beam is also calculated from the Flexural Shear Crack Model proposed by Huber et.al and it is seen that the shear capacity from the numerical analysis from ATENA is in close match to that obtained from the analytical model. The contribution of the arching effect to the shear capacity calculated from the model is between 77% and 87% for the beams tested in this research and the contribution is between 28% and 58% in the beams tested in the experiment. In the last step, the effectiveness of strengthening the reference beam with UHPFRC is determined. The results show that the effect of strengthening with UHPFRC is maximum in the reference beam without stirrups and prestressing both in terms of shear capacity and ductility.

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The bridges built in the 50’s, 60’s and 70’s are reaching the end of their originally service life. Many bridges require reassessment. In 2009 the former ministry of “Volkshuisvesting, Ruimtelijke Ordening en Milieubeheer”(Housing, Spatial Planning and the Environment) carried out a study about the state of the bridges, following several incidents including for example the closure of the Sebastiaansbridge in Delft. The main conclusion from the research was that it is hard to prove that the structural safety of existing bridges and viaducts is sufficient. One of the main topics in the reassessment of the bridges was the shear capacity. The aim of this study is first to investigate the present Eurocode approach to determine the shear tension capacity, secondly if there is a possibility to improve this Eurocode approach or to propose another model. The general main research question is: What model determines the resistance with respect to the formation of shear tension cracks most accurate? Practical experiments of the researchers Choulli[8] and Elzanaty[9] already carried out will serve as a basis to evaluate of differentmodels in this thesis. The experiments consist of single-span prestressed I- and T-beams. The study focusses on two topics. In the first topic attention is paid to the comparison of the analytical stress distribution and the numerical stress distribution of the web of the single span prestressed I- and T-beams. The analytical stress distribution is determined according to the Euler-Bernoulli beam theory, the vertical stress component ¾y is not taken into account. The current Eurocode model is based on the analytical stress distribution. The numerical stress distribution is determined with a linear elastic analysis in the finite element software program DIANA FEA. The following topic is about the choice of a consistent model that predicts the first shear crack in the web and the consideration of a strength criterion. In this study in total there are considered 6 models and 3 strength criterions. Model 1 is the Eurocode model and is considered with the analytical stress distribution. Model 2, the “LE FEA” model is considered with the numerical stress distribution. Model 3, the “midheight” model around the neutral axis, is considered with the analytical stress distribution. Models 4, 5 and 6 respectively the 45°, the 35°and the 30°model, are considered with the analytical stress distribution. Each model consists of a single or a set points in the web of the prestressed beams to consider. For both the textual explanation and the graphical representation of the models, reference is made to sections 5.1.1 and 5.2.1. There are considered 3 strength criterions: the uniaxial tensile strength fctm, the biaxial tensile strength according to “Mohr-Coulomb” and the biaxial tensile strength according to “Huber”. For each model, the set of points or the single point is divided by a value of a strength criterion. This is defined as “model uncertainty”. From the analysis it is found that the analytical stress distribution does not equal the numerical stress distribution at some parts of the prestressed beams. This is the case in the socalled “disturbed areas”. These areas are located near concentrated loads, so around supports and external concentrated loads. After analysis it is found that the analytical stress distribution takes a too high principal tensile stress σ1 into account, in the “disturbed areas”. After analysis of the different stress components σx , σy and τxy , it is found that components σy and τxy are the cause of the deviant stress distribution in the “disturbed areas”. The test set consists of in total 29 experiments: 12 experiments of Choulli and 17 experiments of Elzanaty. First the results per model, per strength criterion of the Choulli and Elzanaty experiments will be combined, from which the mean and the variation coefficient of the “model uncertainties” are determined. The conclusion is based on one important feature: the conclusions are based on both the complete set of experiments and on the set of experiments where no flexural cracks have been observed. In case of the set of experiments where no flexural cracks have been observed, also the experiments where the calculated tensile stress in the ultimate fiber exceeds the uniaxial tensile strength fctm are left out. From the comparison of the analytical and the numerical stress distribution it can be concluded that stress distribution in the socalled “disturbed areas” is overestimated. Based on the complete set of experiments, model 3, the “midheight” around the neutral axis, is preferred. This model offers the best consistency. Concerning the strength criterion: there is a little difference in consistency between the model with uniaxial tensile strength and the model with the biaxial tensile strength(this holds true for both “Mohr-Coulomb” and “Huber”). Based on this it is preferable for practice to reduce the uniaxial tensile strength with 20%. Based on the set without the experiments which showed flexural cracks, it is found that the “means” of the models were lower and that the models are more consistent. Concerning the strength criterion: both the uniaxial tensile strength fctm and the tensile strength according to “Mohr-Coulomb” are overestimated. For future research it is recommended to investigate the influence of present flexural cracks on the stress distribution, what will be the influence on the way of predicting diagonal tension cracking. Fromthe results in this study it can be seen that the presence of flexural cracks can have significant influence on the consistency of the models. Further, it is also important for future research to consider distributed loads in addition to concentrated loads, because in practice there will be always present a significant distributed load. ... Read more

Vanuit Rijkswaterstaat is de wens om een snelle, verifieerbare methode te ontwikkelen voor het controleren van de veiligheid voor meerdere T-ligger constructies volgens huidige normen en inzichten. Hierbij dient rekening gehouden te worden met eventuele wijzigingen in de toekomst, welke door de huidige ontwikkelingen op het gebied van dwarskrachtonderzoek te verwachten zijn. Het is de verwachting dat op basis van verfijnde beoordelingen en verder fundamenteel onderzoek de ‘reserves’ middels een quickscan-aanpassing inzichtelijk gemaakt kunnen worden. Hierdoor zou een deel van de onderzochte kunstwerken mogelijk alsnog voldoen aan de veiligheidsnormen.

Door diverse berekeningsmethoden met elkaar te vergelijken is getracht een methode te vinden welke simpel toepasbaar is, realistische resultaten voor dwarskracht en moment geeft ten gevolge van de verkeersbelasting en tevens conservatief is. Door deze te vergelijken met diverse Scia-berekeningen is een methode gekozen die het best aan de eerdergenoemde punten voldoet. Tevens zijn de invloeden van meerdere uitgangspunten met elkaar vergeleken. Nadat inzicht is verkregen in de manier waarop de belasting over de liggers is verdeeld, is een generiek systeem gemaakt, een zogenaamde quickscan. De quickscan maakt op een snelle manier duidelijk of de gekozen snede voldoende weerstand kan bieden aan de behorende belastingcombinaties. De quickscan is een generieke, eenvoudig toepasbare, conservatieve methode om ‘het kaf van het koren te scheiden’ voor de dwarskrachttoets, zonder dat daarvoor EEM-software nodig is, welke tevens de Scia-berekeningen zo goed mogelijk benadert. Om deze zo goed mogelijk te ontwikkelen is een beoordelingsprocedure gerealiseerd welke zich vormt tot de quickscan.

Om inzicht te verkrijgen in de invloed van de verkeersbelasting op de liggers en om deze conservatief te benaderen, zijn diverse berekeningsmethoden met elkaar vergeleken.
Uit deze vergelijking is gebleken dat de beste benadering voor de verkeersbelasting de ‘verspreide methode’ is. Hierbij wordt de belasting gespreid of is deze niet afhankelijk van de locatie van de dwarsdragers. Met deze kennis is de quickscan Boon ontwikkeld. Deze kan worden uitgevoerd door enkele parameters in te vullen, zoals: de lengte van de ligger, het oppervlak van de ligger, het voorspanverloop, de dwarsdragers en door de ‘kritische’ sneden (belangrijke te toetsen sneden) van de ligger te bepalen. Daarna kan snel en slim inzichtelijk worden gemaakt wat de UC op deze sneden van de constructie is, en wat de consequenties van wijziging van uitgangspunten zijn. Uit het onderzoek is gebleken dat het tandemstelsel altijd op een hoek van 30 graden vanaf het gekozen punt tot hart rijstrook moet staan om de maximale dwarskracht in dat punt te vinden. Deze belastingsposities worden automatisch gevonden, waarna direct de dwarskracht en het bijbehorende moment berekend wordt met behulp van de verspreide methode. Hierdoor kan de constructieve beoordeling van de liggers snel inzichtelijk worden gemaakt.

De quickscan Boon is een eenvoudig toepasbare, realistische, conservatieve beoordeling voor T-ligger constructies, welke inzicht geeft in de maatgevende belastingcombinatie en gemakkelijk te verifiëren is. De kracht van deze methode is dat door te variëren met diverse parameters (zoals capaciteitsaspecten, te toetsen snede en rijwegindeling) direct de invloed van deze parameters inzichtelijk kan worden gemaakt. Waar de resultaten conservatief en toch reëel zijn.
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This Master Thesis is about the comparison of the effective concrete tension zone height determined with either finite element models using DIANA or Eurocode 2 and Jones method. The effective reinforcement ratio is an important parameter for the determination of the crack width and is depending on the effective concrete tension zone height. Therefore a better understanding of the effective concrete tension zone height can be beneficial for the determination of the crack width. Especially for structures with multiple layers of reinforcement. The finite element models have been used to check whether the assumptions made in Eurocode 2 and Jones method are correct for the determination of the effective concrete tension zone height. ... Read more

When engineers at Tunnel Engineering Consultants (TEC) used the Eurocode 2 (EC2) for the verification of flexural cracks in cross sections of immersed tunnel elements, they found out that there was more reinforcement needed for crack width limitation than for tensile strength of the reinforced concrete. This raised questions, namely whether the extra reinforcement is needed, how accurate the EC2 calculates the crack width and what the influence is of the construction height on the crack width?

Are the current rules in the Eurocode 2 for the calculation of flexural cracks too conservative for large thicknesses that are applied in the concrete lining of immersed tunnels?

In this thesis the crack width calculation of the EC2 has been compared with other codes around the world. When these codes are compared with each other it seemed to be that the EC2 is not conservative in comparison with the other codes, however it does not directly mean that this is true.
To check whether the codes, especially the EC2, are conservative, the codes should be compared with laboratory experiments. Since there is little data of experiments available where the cracks are carefully measured, in particular beams with large thicknesses, the finite element program DIANA is used to gain more data sets. A DIANA model is validated with three different experiments with each a different height.

When the EC2 and the DIANA results are compared, a few differences are found. The predicted crack widths in the EC2 are larger than that of the DIANA results. In the EC2 the crack width is the multiplication of the crack strain and crack spacing. If these values are compared, the EC2 gives a smaller crack strain than DIANA and therefore the crack spacing gives an even larger difference than the crack width. Next to that, the influence of the parameters in the EC2 is analysed. In both the EC2 and the DIANA results the cover is the most important parameter for the crack spacing and the steel stress of the reinforcement is the most important parameter for the strain. In all the results there is almost no effect of the construction height visible, except in the crack strain of the DIANA results when the cover is relatively large. A decrease of strain with an increase of height has been detected.

The differences in crack strain can be explained by the fact that the strain in the EC2 is calculated at reinforcement height, but the strain at the outer fibre is needed. In axial loaded cases these strains are the same, but in cases where the cracks appear due to bending moments, which is the case in this thesis, the strain is bigger at outer fibre. Next to that it seemed that influence factors used in the crack spacing calculation are overestimated, but no clear reason is found for this result.
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Coda wave interferometry is a technique used in the field of seismology, which utilizes the later part of the signal (coda) to detect subtle changes in a medium. In recent years, the application of coda wave interferometry to concrete structure has been assessed for structural health monitoring purposes. Smart aggregate is a sensor which consists of a piezoelectric sheet which is sandwiched between two marble layers which are meant to be used for structural health monitoring purposes by embedding it into concrete. However, its implementation for coda wave interferometry applications had not been attempted previously. In this research, the application of coda wave interferometry in concrete structures is explored further. The aim of this research is to assess the possibility of implementing coda wave interferometry to monitor the hydration process and the evolution of elasticity-modulus of concrete, as well as to learn how the wavespeed changes in concrete specimens subjected to cyclic loading in compression and bending. Additionally, seismic interferometry is also attempted to retrieve virtual impulse response to be used for coda wave interferometry. All experiments in this research utilize smart aggregates as transducers. By implementing coda wave interferometry, it is found that wavespeed does increase as concrete ages. This wavespeed increase can be linked to the evolution of elasticity-modulus of concrete, which enables its value to be monitored through the utilization of coda wave interferometry. It is also found that the use of embedded smart aggregate yields excellent reciprocity and stable correlation coefficient throughout the recording, while attached smart aggregates do not perform as well as the embedded ones in terms of reciprocity and correlation coefficient. Positive linear wavespeed change vs. stress and strain relationships in compressive samples are observed in lower stresses. In higher stresses, both wavespeed change vs. stress and strain display gradient reductions. Under repeated cyclic loadings, the loading phase of the first load cycle tend to have lower initial wavespeed change vs. stress and strain gradients compared to the following load steps, and the wavespeed change vs. stress and strain paths of reloading phases tend to follow the paths of their previous unloading phases. Wavespeed change vs. strain is more representative compared to wavespeed change vs. stress in depicting the compressive specimens’ condition due to the occurrence of permanent deformation during loadings. In a 10m-long beam specimen subjected to bending and shear, coda wave interferometry of later arrivals reveal decrease in wavespeed in the first loading phase of the test, while earlier arrivals show increase in wavespeed in the same phase. Moreover, it is possible to detect major crack formations by utilizing coda wave interferometry, which sensitivity is determined by the location of the cracks relative to the source-receiver sensors’ proximity. By assessing earlier arrivals of the signals recorded by smart aggregate implanted in the compression zone, the shift from uncracked to cracked section is observed through changes in wavespeed change vs load gradients. Seismic interferometry attempt was unsuccessful due to poor repeatability of the hammer hits and insufficient illumination to create diffuse wavefield. ... Read more

Finite element analysis is becoming a popular tool for engineers recently. Nonlinear finite element analysis is more advanced due to that it can deal with the nonlinearity of structures, which leads to more accurate approximation of structural behaviour. In Model Code 2010, nonlinear finite element analysis, which belongs to the higher level of approximation, can predict the structural behaviour with refined physical parameters but by devoting more time to the analysis. This leads to better accuracy. Thus, it is important to study how to apply nonlinear finite element analysis to approximate the structural strength.
When it comes to the existing design codes, the shear design methods of reinforced concrete slabs loaded in uniaxial in-plane force are developed from the tests of beams rather than slabs, which may lead to the underestimation of the design resistance. Through experiments of seven slabs, a related study of the validity of existing shear design methods has been performed by Bui et al. (2017). However, there is no existing literature about the application of nonlinear finite element analysis towards the reinforcement concrete slabs mentioned above so far. In this thesis, one single nonlinear finite element analysis is applied to seven slabs of experiment to study the validation of nonlinear finite element analysis on the RC slabs without shear reinforcement loaded in concentrated out-of-plane load and uniaxial in-plane loads. The validation is studied by comparing results from finite element analysis, experiment and finite element analysis from Nana et al. (2017), which mainly includes shear load – displacement curve, development of crack pattern, failure modes and the influence of uniaxial load on the structural behaviour. In addition, the shear capacity under uniaxial in-plane load is studied by comparing results from analytical assessment based on existing codes, experiment and nonlinear finite element analysis.
When compared with experiment, nonlinear finite element analysis shows a close shear capacity of all seven slabs but stiffer structural behaviour. The development of cracks is similar to the observation of experiment. The failure modes indicated by nonlinear finite element analysis is more likely punching shear rather than one-way shear that is demonstrated in the experiment. The influence of increasing uniaxial compression on shear capacity is larger than what is observed in experiment while increasing tension has smaller influence. By comparing the prediction of shear capacity from experiment, existing codes and nonlinear finite element analysis, it can be concluded that NLFEA is unconservative in prediction of shear capacity of the RC slabs without shear reinforcement loaded in concentrated out-of-plane loads and uniaxial in-plane loads. Some suggestions are given for further study. Improvement of modelling is suggested. For instance, finer mesh could lead to more accurate results, and insights of bond-slip reinforcement could generate more precise results. Furthermore, the study of safety formats is suggested in further study to consider the uncertainty due to random variation of material properties. In addition, more experiments and nonlinear finite element analysis are suggested to get insights of the influence of uniaxial loads on structural behaviour of RC slabs without shear reinforcement.
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Underground infrastructures and the importance of the people’s safety and structures robustness are relevant and contemporary issues in the civil engineering industry. The demand for this infrastructural typology has developed to such an extent that the need for a better and cost-beneficial knowledge of the risks is necessary.
This thesis aims at bridging and developing further the knowledge on Fire safety engineering and structural engineering on the particular topic of spalling failure. Another objective of this thesis is the discussion over the possible replacement of the used procedures used to assess and guarantee tunnel safety. Both from a fire safety and structural engineering point of view, prescriptive measures and solutions are mostly proposed to accomplish a safe tunnel design. This causes the design to be non optimised and in some cases more costly than what is actually needed.
From the fire safety side, the use of pre-given fire curves is put under discussion. Research has been conducted to asses which are the origins of the most widely used curves. Studies have also been performed to develop a practical analytical engineering method to analyse and estimate the consequences of a given fire scenario tailored to the specific tunnel under consideration. Subsequently the results of the analytical models have been compared with the results obtained with advanced Computational Fluid Dynamics tools. Finally, more complicated scenarios have been studied with the use of this software.
On the other hand, from a structural engineering point of view, a new model able to describe the spalling mechanism has been proposed. The model predicts the spalling time for NSC elements and at the same time verifies which is the optimal thickness for the piece to spall. On top of that the possibilities for further use of the model in the description of the spalling mechanism for HSC and PPFRC elements have been investigated.
Finally this two topics have been combined together and conclusion have been drawn.
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This master thesis covers the research into cracking behaviour of slender high strength concrete cantilevering balconies. The research emerged from Pieters Bouwtechniek Delft and Hi-Con Denmark. They cooperatively designed very slender balconies in ultra-high performance fibre reinforced concrete. Other engineering firms tend to recreate these balconies in HSC and insecurities emerged around the cracking behaviour and crack width prediction for these slender HSC cantilevering balconies. In addition to this research an informative report, also functioning as a literature study, on the connection of prefabricated concrete balconies is produced. This report is separately attached.

The research is step wisely conducted starting with a simple fully clamped cantilevering slab. For this slab the cross sectional height, reinforcement diameter and reinforcement spacing are varied to investigate their influence on analytical crack width predictions. First for all variants an analytical design and analysis process is executed, followed by a numerical analysis with DIANA FEA and a comparison of the results. The most important observation is that for a cross sectional height of 120 mm or smaller reinforcement bars are located outside the effective area, making the analytical method unsuitable. Furthermore, a big discrepancy between the predictions of the different analytical models is observed, indicating an unreliability of these methods.

In two steps the fully clamped balcony is transformed into a Hi-con shaped balcony executed in HSC. It appeared that in light of detailing rules from Eurocode 2 an exact reproduction is impossible, but the concept could be reproduced in a less slender way. Furthermore, by comparing analytical and numerical design results for two different balcony designs it is found that the accuracy of the analytical crack width prediction depends on geometric disturbances. In case a geometric disturbance is present in a slender area loaded in tension peak stress concentrations occur, which negatively influence the reliability of the analytical crack width prediction. In case the area is less slender, the effect is less pronounced and the conservative characteristics of the analytical method outweigh the influence of the concentrated peak stresses.

When summarizing, it appears that specific care should be taken when analytically predicting crack widths in slender balconies because it might appear that the reinforcement is not located in the effective area. Furthermore, the more slender the structures become, the bigger the influence of a geometric disturbance can be, increasing the risk of an underestimation of the occurring crack widths because peak stress concentrations are analytically not accounted for.
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Soil-mix walls are subsoil walls, which are constructed by in situ mixing of soil
with cement and water. The technique was initially used as a ground improvement
technique and is now being developed as construction method for walls
with a structural purpose. Currently these walls are reinforced with large steel
profiles, which requires a large quantity of steel. Replacing the profiles with
bar reinforcement might lead to a decrease in required material quantity and
thus a reduction of material costs.
There are multiple aspects which influence the possibilities and limitations
of bar reinforced soil-mix walls. These include predictability of the material
quality, durability and cooperation between soil-mix and the reinforcement.
The aim of this project was to contribute to this research by analysing one
of the influential aspects. The specific goal of this research project was to
analyse the capacity of a reinforcement detail within a soil-mix wall and define
the governing failure mechanism. The research combined an experimental and
numerical approach to the subject.
The critical detail was chosen based on the Huybrechts et al. (2016), Ganne
et al. (2010), Dörendahl et al. (2004) and contact with soil-mix experts. To
model this detail in a finite element model, in 2D and 3D, material parameters
were derived from Denies et al. (2012a), Denies et al. (2014), Denies et al.
(2015a) and performed physical tests. The 2D models represented the most
critical sections of the detail based on the theoretical stress distribution. The
geometrical parameters of the reinforcement design were varified in the models
to provide insight in the influence of the design on the capacity.
The model results were used to define an preliminary set of design guidelines
for the reinforcement cage, related to the depth of the wall. Since only
the capacity of the detail is considered, these guidelines are not suficient for
a complete design of a bar reinforced soil-mix wall and can only serve as an
initial indication.
In conclusion, the reinforcement detail is most sensitive to failure due to vertical
splitting and has suficient capacity for acceptable wall depths. As stated
before there are multiple aspects relevant to the feasibility of bar reinforced
soil-mix walls. The predictability of the material quality, the bond with the
reinforcement and the durability of the soil-mix strongly influence the final
capacity and behaviour of the wall. Therefore it is important to perform further
research on these, and other, aspects to conclude on the total structural
integrity of an entire bar reinforced soil-mix wall. ... Read more

Strain hardening cementitious composite is a new generation material with increased ductility and improved cracking behaviour as compared to traditionally used Normal Strength Concrete (NSC). An important charactersitic of SHCC is the ability of the fibers (2% PVA) in the composite mixture to bridge the cracks and there by preventing localization of cracks, resulting in a narrow network of cracks with width less than 100 micron (Micro cracking). The aim of this research is to investigate the possible benefits of having a layer of SHCC in the tension zone of a reinforced concrete beam under four point bending test. A numerical simulation of the four point bending test is performed using a finite element software called ATENA. Comparison is made between traditionally reinforced concrete beams and beams with steel reinforcement embedded in an SHCC layer. The load capacities and crack patterns might present us with opportunity to understand the influence of an SHCC layer in tension zone of a beam under bending. ... Read more

The aim of this thesis is to investigate the behavioral differences of walls that have different load transfer mechanisms and identify a simple engi- neering model for a construction joint that connects these two different wall types.
Within the text; First, the problem description is provided among with a simple yet reliable soil modeling for finite element method, to illustrate the excavation work. Then, six engineering models have been constructed and analyzed and results are compared. Phased excavation in layered soil is performed by shell and interface elements provided by the FEM package Diana 10.1. In addition, the section forces are estimated for an upper and lower bound given for different wall mechanisms. To conclude, the criti- cal construction stage and the critical depths are reached. Expected section forces are computed and compared with the capacity of the critical con- struction joint.
This thesis highlights the reliable and simple modeling of a laterally supported phased excavation analysis. Furthermore, it outlines the factors effecting the resulting forces from different load transfer mechanisms and concludes that the critical section subject to this thesis is safe with the given conditions. . . . ... Read more

The role of the slab mechanism compressive membrane action is investigated, during the direct loading of a beam integrated in a prestressed deck bridge. ... Read more

Bridges are a crucial part of the dense Dutch highway network. Almost 50% of the current bridges are built between 1960 and 1980 for an intended service life of 50 years and thus they might reach the end of their lifetime in the near future. This strongly indicates that a large challenge can be expected regarding infrastructural replacement.
In current practice, the replacement of bridges within the highway network often leads to substantial traffic hindrance, which has a large negative impact on the Dutch economy. Therefore reduction of traffic hindrance – together with sustainability – is generally an important quality criteria in MEAT-procedures (Most Economic Advantageous Tender) for tender assignments. In order to prepare for the upcoming replacement challenge, there is a need for contractors, the government and product suppliers to invest in the development of a sustainable tender strategy now.

The main objective of this thesis was to propose a tender strategy that incorporates sustainability and in particular the reduction of traffic hindrance into a technically feasible design. An extensive literature review has led to a quick bridge replacement strategy consisting of three time-reducing actions, listed according to their potential profit in construction time:

1. Select the Accelerated Bridge Construction (ABC) approach:
By means of lateral sliding or transportation by SPMTs (Self-Propelled Modular Transporters) entire superstructures can be constructed off-site and transported to their final location in a matter of hours.

2. Retain the existing foundations:
In terms of on-site construction time it would be beneficial to retain the existing foundations. Additionally, theory suggests that a profit in bearing capacity can be obtained compared to the current design codes, which might lead to the total elimination of additional foundation elements required.

3. Avoid intermediate supports:
Less elements are required if intermediate supports are avoided in the new bridge design. This does however lead to longer spans, and to prevent additional groundwork activities from an increase in deck height a higher slenderness must be obtained. Furthermore, the new superstructure design must be as light as possible, not only to allow for foundation retainment, but also to facilitate transportation and speed of erection.

In particular, the technical feasibility of these actions - both separately and combined - required more research. A case study considering a two-span plate bridge was used to investigate these strategy actions. Research was done into the obtainable profit in retained pile foundations and the application of UHPC in a slender and lightweight bridge concept.

It was concluded that the proposed tender strategy has a high potential. Not only is the on-site reduction time diminished but the retainment of the existing foundations and the application of UHPC in a slender and lightweight superstructure may also lead to a highly sustainable design.
... Read more

An increasing number of existing structures are approaching the end of their technical service life. Therefore, monitoring these structures to get the information of their health condition, which is called structural health monitoring (SHM), is becoming more significant. In SHM, acoustic emission (AE) technique shows promising features in detection, localization and characterization of damage. This technique has been applied in many fields, such as steel structures, composite structures and concrete structures. In dealing with existing concrete structures, cracks can influence the features of AE signals when they are on the way from the defect to the sensor. Therefore, it may challenge the commonly-used notion of AE monitoring. The influence of crack on AE monitoring has not been sufficiently investigated. More quantitative assessment on the crack influence on AE signals is believed to be valuable for the evaluation of accuracy and reliability of AE monitoring of existing concrete structures. In this research, the influence of crack on AE signals has been studied quantitatively. Experiments on cracks with different opening have been performed to support the formulation of the signals. The results are then used as inputs for an analytical study on source localization influenced by a crack. A three-dimensional (3D) triangulation technique has been used for source localization on a modeled cracked concrete beam. Localization error can therefore be estimated for AE sources in the presence of existing cracks. Furthermore, the influence of a crack on the amplitude of AE signals has been discussed. With the demonstrated crack-induced errors and attenuations ranges, the results can provide insights to the accuracy and reliability of AE monitoring in practical situations. ... Read more

In this study the cracking and debonding behaviour of cementitious screeds bonded to concrete bearing floors is
analysed. In order to obtain insight in this behaviour research is performed to the surface tensile strength of concrete,
the bond strength of screeds on concrete bearing floors, the behaviour of screeds during shrinkage and the methods to
determine the bond strength. This research is carried out by a theoretical study in which the screed shrinkage
behaviour as well as the screed / concrete behaviour during testing of the bond strength is analysed by means of
analytical and FEM studies. Besides this practical experiments are performed to obtain insight in the influence of
different parameters on the surface tensile strength of concrete / the bond strength of screeds on concrete bearing
floors. Furthermore practical experiments are executed to study the influence of different parameters on the outcome
of a preferred bond strength testing method. ... Read more