The main objective of this research is to understand the development of arch action in a single T-beam acting as part of the bridge system, ignoring the distribution of the load in transverse direction. As the beam is loaded, several mechanisms work simultaneously in the bridge system, resulting in enhanced ultimate load bearing capacity of the bridges, like compressive membrane action (CMA) in deck slabs and arch action in concrete beams. For this research, an approximate analytical model for quantification of arch action in underwater concrete slabs loaded with uniformly distributed loads (suggested in CUR-077) is verified using non-linear finite element analysis for varying span-to-depth ratios, stiffness of lateral restraint and initial prestressing in the system. The adopted analytical model seems to be able to conservatively predict the arching capacity (within 12%), horizontal stretch (within 10%) and membrane forces (within 10%) in concrete members when compared to the numerical models, provided that the slenderness is less than 15 and the stiffness of end-restraint is at least equal to the stiffness of restrained member. The verified analytical model is then extended to beams loaded with concentrated loads and within the central half of the span, the adapted model is able to conservatively predict the arching capacity with an accuracy of at least 15%. The analytical model is then further extended to beams with T-shaped cross-sections for uniform and concentrated loads. These models are able to predict the arching capacity in T-beams with an accuracy of 7.5% when the numerical failure is due to crushing of concrete. In T-beams with thin webs, the strut failure is observed and the adapted models are not able to predict the arching capacities. As a case-study the Vechtbrug beam is modeled using 2D, 2.5D and 3D approaches in DIANA and the models are validated using the experimental work done by Ensink as part of his PhD studies. All the models show comparable load-deformation behavior and peak loads (within 7%) but only the 3D model is able to simulate the crack pattern observed during experiments. The validated numerical model of the Vechtbrug beam is then adapted as though it is connected to the bridge through cross-beams by applying full restraint at the edge faces of the cross-beams in longitudinal direction. The arching behavior of the adapted Vechtbrug beam model is compared with a disjointed bridge model developed by Ensink in which the distribution of the load is prevented in transverse direction by disconnecting the slab of the loaded sub-span with neighboring beams. Applying full restraints at the edge faces of cross-beams is found to overestimate the influence of arch action in the loaded sub-span when compared to the disjointed bridge model. The adapted analytical model for arching in T-beams with point loads is applied on the loaded sub-span but is found unable to conservatively predict the arching capacity owing to the thin web of the Vechtbrug beam causing strut failure, which is not taken into account by the analytical model.

Recycled granular materials such as Recycled Concrete Aggregate (RCA) and Recycled Crushed Masonry (RCM) are widely used in The Netherlands as base layers in asphalt pavements. The lack of natural resources and the growing amounts of demolition waste made that the Dutch industries in the early 1980s started to explore the possibilities to use construction debris in road construction. Recently, the application of recycled materials in pavement structures has also found traction in South Africa. Due to differences in pavement design, however, the mechanical and environmental exposure of these materials will be more severe than in the Netherlands. This results in different challenges with respect to (long term) performance and material durability. Understanding the potential durability issues and the way durability affects pavement performance is crucial to successfully implement these materials in South African pavements.
This research, conducted at Stellenbosch University, South Africa, involves laboratory testing to investigate the performance and durability aspects of recycled aggregates. By means of triaxial testing before and after durability simulation, it is aimed to address the extent of potential material breakdown and the influence this has on performance. Tests are conducted on RCA, RCM, MG65 and MG30. The latter two refer to a mixture of RCA and RCM, with a mass percentage RCA of 65% and 35%, respectively. In addition to the recycled materials, a commonly used crushed rock of G2 quality is tested as well to serve as benchmark. Monotonic triaxial tests, to obtain the shear parameters, are performed on all materials except the pure RCM. Permanent deformation triaxial tests, to gain understanding of the long term response to cyclic loading, are performed on RCA and MG65. Specimens are tested under different confinement and deviator stress levels. For the durability simulation, the South African Durability Mill (DMI) is used. The DMI enables durability testing of the full grading under soaked and dry conditions. After the tests, the milled specimens are sieved out to obtain the change in grading.
The most important findings regarding granulate durability include that the breakdown in recycled materials is significant in comparison with the G2. Mainly the largest particle fractions are affected. Furthermore, for these particular resources of recycled granulates, the RCA suffers more breakdown than the RCM. The breakdown in the blends decreases with increasing masonry content, implying that the RCA is the most prone to mechanical damage. Considering the monotonic triaxial tests, substantial values of shear parameters are measured in all materials. The highest cohesion is measured in the MG30, while the highest internal angles of friction are measured in the pure RCA. The shear parameters in the recycled materials are in all cases higher than those for the G2. Differences in failure type (brittle versus plastic) are observed as well. Durability milling results in a small increase of the internal angle of friction and in a moderate decrease of cohesion. The latter is the most governing for the material’s compressive strength after milling, as this is decreased in all milled specimens. Still, the shear parameters of the milled specimens remain relatively high. In the permanent deformation triaxial tests, a decrease of performance can be observed in both the RCA and MG65. Delayed shear failure is observed in milled specimens tested at a deviator stress ratio (DSR) higher than 30%. Although the number of permanent deformation tests performed in this research is limited, 30% DSR seems the upper limit with respect to cyclic loading. This points out that monotonic triaxial testing alone is not sufficient for an adequate material characterization. A small linear elastic pavement analysis based on the tested materials, however, shows that the occuring DSR levels in a reference pavement caused by standard axles of 80 kN do not exceed 20% DSR, proving the potential of these materials for further studies.

In the past, many researches on the topic of size effect on concrete structures were mainly focused on the phenomenon of size effect in flexural cracking. The result of those studies can be found today in the concrete structure design specifications of well-known building codes, such as the Eurocode. Nevertheless, the inclusions of the results of those studies into the design specifications are still minimum and therefore, it is necessary to conduct more studies on size effect, especially on other types of cracking.
In this thesis, an investigation focused on the size effect in shear tension cracking at prestressed concrete beams was conducted. The model used for investigating the size effect is a prediction that a shear tension crack will occur when the principal tensile stress at a certain location on the web of a beam is equal to the concrete mean uniaxial tensile strength (σ1 = fctm). The investigation was conducted by studying premature shear tension cracking on a group of several I-profile prestressed reinforced concrete beams, called the trusted specimens, which were experimented by Hanson (1964), Choulli (2005), and Elzanaty (1986) under four-point bending tests. These tested beams were numerically investigated using linear elastic finite element analysis (LEFEA) with an aim to find the nearly realistic principal tensile stresses that caused the shear tension crack to initiate below the designated tensile strength of the beams.
To study the size effect, the obtained principal tensile stress distributions were analyzed using two new approaches proposed by the author, namely the σ1 area approach and the ratio-of-distances approach. The σ1 area method is a technique for detecting a structural size dependency of the uniaxial tensile strength by comparing rectangles which areas represents a group of σ1 values that have a higher likelihood in achieving the deviated values of fctm and initiate shear tension cracking on the web of the trusted specimens. In contrast, the ratio-of-distances approach investigates the size dependency of the uniaxial tensile strength by observing the locations of σ1max where a shear tension crack initiated in the web of each trusted specimen under an assumption that a shear tension crack is more likely to originate from near the beam neutral axis instead of near the web-flange junction due to the change of thickness at that interface.
In conclusion, the result of the investigation was presented. The σ1 area approach confirmed the presence of size effect in shear tension cracking at the trusted specimens by giving a relation that showed a tendency for the smaller specimens to have a higher resistance towards principal tensile stresses compared to the larger specimens. The ratio-of-distances result, on the other hand, implied that the approach has failed to detect the presence of size effect. In that result, the shear cracks from the smaller specimens and the shear cracks from the larger specimens had similar starting points locations, at which the σ1max was located.
In addition, several recommendations are provided for future studies on size effect in shear tension cracking. It was recommended to do research this topic on different physical problems and shear tension cracking with the presence of flexural cracks.

Müller Verpress piles are driven displacement piles which inject grout at the enlarged tip of the pile into the surrounding soil. Performed full-scale tests were not able to be loaded the pile upon failure, as the pile can resist forces which are significantly larger than its design capacity. This type of pile is known for its large tensile capacity and it is used often to bear major loads in large structures, but the ultimate true capacity has not been identified yet. A better understanding in the behaviour of a MV pile can be crucial in an optimal design of such structures, as construction costs and obtained safety level can be reduced. From provided full-scale tests the uncertainties about the shape of the circumference of the injected grout body and the acting soil pressures have been reduced. Further a different relation is found between the mobilized shaft friction and the cone resistance. As the soil becomes stiffer and holds a larger cone resistance, more shaft friction is mobilized.A two-dimensional numerical model of a cross section of the pile is generated to obtain the actual shape of the circumference and the maximum shaft friction after installation. The measured grout discharges and mobilized shaft friction from pile tests were in the same range as the results obtained from this model, validating that the results of the model are within reason. All available full-scale tests were extrapolated by application of the model and generated similar capacities as the method by measured shaft friction, setting a minimum boundary for α_t at 1.4%. A second numerical model of a complete full-scale tested pile is successfully generated, including the adaptations of obtained parameters from the other model. The adaptations consist of a new circumference, different relation for EA and larger values for the maximum shaft friction. The model showed results which are in the same range as the analytical derivations regarding the course of forces and mobilized shaft friction. The modelled results do however differ slightly in value. This difference in results can be explained by the absence of detailed soil investigation. The lack of detailed geotechnical parameters would increase the accuracy of the model, as the model is very sensitive to variation in the geotechnical parameters. The produced adaptations of multiple parameters have proven however to be a better indication of the total capacity than the current norms. Therefore the norm can be adapted into a more progressive code based on the produced relations of this thesis. The adaptations in EA relation, circumference and mobilized shaft friction comprehend the behaviour of the Muller Verpress pile with a better understanding. Changing these parameters are preferred over the adaptation of the α_t factor, as the theoretical background remains in the design rule.

With the arrival of the Eurocode, the calculations regarding shear resistance, have become increasingly conservative compared to former concrete standards. For example in Voorschriften Beton 1974 (VB 74), a former concrete standard, a shear resistance combination of concrete, stirrups and prestress was allowed. Whereas the Eurocode assumes the shear resistance of the concrete is zero if it’s standalone contribution is insufficient. Meaning that once stirrups are required, the total applied shear stress is controlled by the stirrups.
Prorail is the party in the Netherlands which is responsible for the construction and maintenance of the railway infrastructure. The change in regulations results in concerns for parties like Prorail and in particular to the shear resistance of concrete railway bridges constructed according to the VB 74.

A through railway bridge consists of a relatively thin floor and two prestressed girders. Whenever a train drives over the floor, a great deal of the loading is spread in transverse direction, causing large shear forces and torsion in the two prestressed girders. Because this combination can be critical for the shear resistance, two prestressed through railway bridges, constructed according to the VB 74, are investigated in this master thesis.
It is verified with hand calculations whether or not these existing structures can guarantee structural safety by considering three shear resistance checks; the risk of shear tension failure, capacity of the stirrups and resistance against fatigue. Ultimately it is concluded, that the largest unity check is 1,01 and that both bridges can guarantee structural safety regarding shear resistance.

The reassessment of an through bridge, is an typical assignment for engineering firm such as Witteveen+Bos. But because hand calculations are too time consuming, the design loads are determined with SCIA Engineer (FEA program).
However in the earlier days FEA programs were not available and torsion in the girders was derived from a set of differential equations (analytical solution). Because structural engineers from today completely rely on programs like SCIA, a comparison is drawn up between SCIA and the analytical solution for torsion in the girder.

The plate, beam model 1A and 1B are the three types of models available in SCIA to model a through bridge. The plate model consists of a 2D-floor and 2D-girder, where the beam models form a combination of a 2D-floor and 1D-girder. But the plate and beam model 1B have in common that rigid connections are applied every ¼ meter between the girder and floor.
The analytical solution is derived with the assumption that the bridge is divided into strips with a length of 1,0 meter, which is implemented in the plate and beam models by reducing the E-modulus of the floor to roughly a third (cracked floor). For the governing load combination, this leads to values for torsion, which remain 10-15%, 40% and 10% behind the analytical solution for respectively the plate and beam model 1A and 1B. The large deviation of beam model 1A is remarkable and can be explained from the fact that no rigid connections between the girder and floor are applied, resulting in a loss of bending and torsional stiffness of the girder.

To conclude, the analytical solution is based on a number of assumptions, like no load distribution of the floor in longitudinal direction. In reality loads will be as well distributed in longitudinal as transverse direction and the analytical solution therefore needs to be considered as an safe upper limit.

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.

Collapse of partially or fully submerged river bridges as a result of river floods is investigated. To this end, post-failure analysis of a bridge in Japan’s Iwate Prefecture that collapsed in 2013 is conducted. Failure of this particular bridge is atypical because piers have also toppled over, which can be attributed to the spread footing foundation not anchored to the bedrock.
Two hypotheses are formed regarding the failure mode of this bridge. One assumes that initially the deck was dislodged and the piers subsequently toppled over, while the other follows the scenario of simultaneous failure of deck and pier. In order to predict which failure mode is governing, estimates of hydrodynamic forces based on design standards and previous research are formulated in conjunction with an analysis of the capacity of a potential bearing type.
Experiments in a flume are performed at a 1:37 scale to simulate steady-state hydrodynamic forces on the bridge. The flow depth and Froude number of the flow are varied across a wide range. Simulated debris is also lodged against the bridge model during some experiments. Observations on under which conditions a free-standing bridge model will or will not fail are carried out. These conditions are then replicated while the bridge model is connected to a load cell to determine the forces associated with failure.
Results show that the resistance against horizontal movement of a bridge deck actually increases as Froude number increases, as negative lift forces dominate over drag forces. Standalone piers always have sufficient resistance against overturning as long as no debris is present. Addition of simulated debris against the pier breaks down its streamlined shape and can cause toppling over of a pier.
Failure of the bridge as a whole (intact deck-pier connection) is not observed under any conditions during the experiments and this hypothesis is discarded. Subsequent failure of deck and pier only happens when simulated debris accumulations are introduced into the experiment. Deck displacement occurs at inundation ratios greater than 2.0 at moderate Froude numbers (0.14 ≤ Fr ≤ 0.32). Pier failure occurs at Fr ≥ 0.34 when the flow depth exceeds the height of the pier.
Possible countermeasures and improvements that may be incorporated into the design of bridges so that they may be more resilient to collapse during a flood in the future are suggested.

Shell is a popular form of structures as it can withstand relative large load with small thickness, which satisfies the aesthetic preference. Due to the curvatures of shell structures, shell can carry the distributed load as membrane forces instead of bending moments. Due to the small thickness, shell structures are highly sensitive to imperfections. As the loads are carried by membrane forces, buckling failure often govern the design of shell structures. The buckling load could be predicted accurately by performing a nonlinear finite element analysis. However, performing a nonlinear finite element analysis is very time-consuming and expensive as a lot of computational efforts required. The currently used design formula of shell structures can lower down the requirement of computation in a great degree while the accuracy is not very satisfying. Different from other types of structures, shell buckling often starts locally, therefore, an assumption is made that shell buckling is a combination of membrane forces and curvatures. Thus, an improved buckling formula is proposed. In this report, the proposed formula is verified and optimized. In addition, the shell behaviour before buckling has been illustrated by a series of figures that show the deformation and stresses at several load steps.

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.