The actual shear capacity of existing reinforced concrete solid slab bridges, constructed before 1960 in the Netherlands, is subject of an extensive research nowadays, since additional sources, increasing the total shear capacity of concrete slabs, have been ascertained to be present. In addition, the increasing occurrence of human-induced earthquakes in the province of Groningen due to gas extraction, arises uncertainties regarding the seismic behaviour and earthquake resistance of existing bridges in this area. The Nieuwklap bridge is a reinforced concrete solid slab bridge located in the Groningen province, combining both characteristics under investigation. In the course of this research, the first two Levels of Assessment have been applied for the static analysis of the slab part of the deck of the Nieuwklap bridge, which was found to have sufficient shear and bending moment resistance under the application of the traffic loading defined by the current standards. The equivalent proof load tandems, that generate the same shear and bending moment stresses, for each load combination level have been found with both approaches, proving that localized phenomena at the area of load application are more intense when the field experiment takes place. Furthermore, by obtaining the equivalent tandem loading that leads to shear and flexural failure of the concrete slab, it has been concluded that flexural failure due to yielding of the reinforcement will occur first in case of exerting the collapse loading on the flexure-critical positions or on the shear-critical positions next to the end-supports. However, in case of applying the tandem loading on a shear-critical position next to a continuous support it is difficult to define which failure mode will precede. Regarding the seismic evaluation of the Nieuwklap bridge, the simplified fundamental mode method and a modal response spectrum analysis have been used. The bridge deck has been found to have adequate resistance against the vertical component of the seismic excitation, which cannot be considered critical, generating nearly the half stresses compared to the traffic load (LM1) combination defined by Eurocode 2. The piers and the pendulums supporting the bridge deck have been also evaluated against the two horizontal components of the seismic excitation, for two different earthquake return periods, discovering that they are able to withstand the generated forces without additional measures. Finally, from the performed modal analysis it has been obtained that movement of the bridge on the longitudinal direction can be observed in lower frequencies compared to the vertical and the transverse direction and that more than 10 modes are necessary in order to describe accurately the bridge behaviour. This Thesis describes the framework that can be used to prepare collapse tests at multiple Levels of Assessment, and for the seismic assessment of existing bridges in regions with recently initiated seismic activity.

Upscaling of two geopolymer concrete mixtures in an individual prestressed girder in self-compacting geopolymer concrete (SCGC) with a topping layer cast in-situ by a ready-mix geopolymer concrete provider. The objective is to study the different material properties of the mixtures, determine their impact in the structural performance and define the extent of applicability of current methods of analysis for conventional concrete structures, as defined in EN 1992-1-1 and the Rijkswaterstaat’s Guidelines for NLFEA, for geopolymer concrete. The structural performance of the elements subjected to flexural (at 28 days and 9 months) and shear (at 28 days) tests is studied by analytical methods and 2D plane stress nonlinear finite element analyses, which are compared to experimental results in terms of deformations, load-deflection response, principal strains, normal stresses, damage evolution, cracking stages, maximum load and failure mechanism; the effect of the long-term material properties (e.g. elastic modulus, creep and shrinkage) of the geopolymer concrete mixtures in the prestressing losses, cracking load and maximum load carrying capacity is analyzed. The elastic modulus of both geopolymer concrete mixtures decreases when exposed to drying and is lower than the estimates from EN 1992-1-1 for OPC concrete of the same strength class. The increase of creep and shrinkage between 30 and 60 days suggest a pronounced viscous mechanical response. The prediction models from EN 1992-1-1 for conventional concrete to determine the material properties from the 28-day compressive strength do not capture the long-term material properties. The isotropic elasticity-based prediction models underestimate considerably the creep coefficient and shrinkage strains leading to unsafe design assumptions. The short-term flexural resistance is higher (8% by analytical model and 3% for the numerical simulation) than the maximum load during testing. The stress distributions at characteristic phases and the cracking load (3% higher than the experiment) are practically equal from the analytical and numerical model. The flexural cracking pattern in the topping in the NLFEA shows more cracks at smaller spacing because higher stresses transfer from the precast girder due to perfect bond. The short-term shear resistance was 12% higher from the numerical simulation and 16% lower from the analytical model, as compared to the experiment. The cross-section of the numerical simulation is stiffer since the precast girder and the topping are perfectly bonded, in the experiment debonding occurred. The position and orientation of the shear critical crack causing failure from the NLFEA was consistent with the DIC observations. The prestress losses at 28 days are higher than for conventional concrete and increase from 26% after 28 days to 38% after 270 days. The variation in the elastic modulus at 28 days has a marginal effect in the short-term response to the flexural test. The cracking load is decreased by 15% in the specimen after 9 months but the prestress losses will continue to increase over time and the cracking resistance will decrease which is critical for the performance over the service lifetime. The design criteria of conventional concrete result in non-conservative estimates of the cracking resistance and flexural load carrying capacity.

In situations with spatial limitations where a bridge is desired, a skewed bridge is a solution. The bridge deck of a skewed bridge has the shape of a parallelogram, in which the angle that remains in the acute corners is defined as the skew angle. This thesis focuses on the design of reinforced concrete skewed slab highway bridges that are simply supported on discrete bearing pads. A parametric tool is created which, based on a set of values for input parameters, generates and analyzes bridge models created in a finite element method (FEM) software program. After analysis, results are summarized, which allows for a parametric study. The goal of this study is to develop knowledge for decision-making in early stages of projects. The influence of main geometric parameters (skew angle, bridge span length, bridge road width) on the load distribution in a skewed bridge is investigated, as well as the influence of FEM mesh element size, applied plate theory, traffic load configuration and support configuration. Another important parameter, being the bridge deck height, is set to be dependent to the span length at first. Skewed slab bridges tend to span from support to support in the shortest direction. This means that loads will concentrate in the obtuse corner. Resultant quantities, mainly bending moments and shear force in the obtuse corner, are studied on their relation with the different parameters. The obtuse corner load concentrations can require the bridge height to become larger than desired. A powerful measure is to add additional triangular sections (ATS) to the side of the bridge, which increases its width. This way, the road skew angle no longer equals the bridge skew angle. Load concentrations in the obtuse corners are reduced, which can result in a lower deck height, less reinforcement, or both. The effect of ATS addition on resultants is studied: great reduction is observed, even for relatively small ATS addition. In order to relate the bridge deck height to bridge geometry, a reinforcement study is conducted. A procedure is described for a certain cross-section, in which the resultants are known from models generated by the parametric tool. Starting point is the longitudinal bending reinforcement based on the crack width criterion, which is usually governing in bridge design. Next, required shear reinforcement is calculated. Following, the ultimate bending moment capacity is checked, which is found to be always sufficient for crack-width-based reinforcement design. Finally, optimization (different bar diameters, add or remove a reinforcement layer, deck height reduction) is investigated and applied if possible. Using the procedure described above, a case study is conducted. A highly skewed bridge (road skew angle of 20◦) is taken. Starting with 0◦, ATS is added in steps of 5◦. For each geometry, a model is created with the tool after which resultants are used for the reinforcement design. For a bridge span of 13.7 m and a road width of 8.3 m, the first bridge (no ATS, skew angle of 20◦) was found to lie beyond the limits of reinforced concrete. Two layers of 40 mm bars required fatigue-sensitive couplers, while detailing and proper anchorage would prove to be unconstructible. Increasing the cross-section also increased governing moments due to concrete self-weight and therefore is not an option. Addition of a 5◦ ATS resulted in a 900 mm high bridge deck, which seems possible to construct. Addition of 10◦ resulted in a 750 mm high deck, 15◦ into 600 mm and further ATS addition reduced deck height even more. Although it should be noted that ATS addition increases deck surface, a significant reduction in deck height can be obtained. ATS addition is shown to be a powerful measure. Depending on project situation, it can provide optimization and cost savings; the parametric tool is proven to be useful in investigating this.

The Helperzoom bridge is one of few existing prestressed slab-between-girder bridges that is being managed by Rijkswaterstaat. These bridges are built before 1980 and do not comply with the current standards. To evaluate the structural safety and capacity these bridges are being assessed. A total of four girders were taken from the Helperzoom bridge, named HPZ1 through HPZ4, and have been destructively tested at TU Delft to determine the shear capacity and failure mode. The first two experiments, HPZ1 and HPZ2, have been considered in this research. Shear-tension failure is one of the failure modes that was being looked for and where the experiments were based on. The most important results of HPZ1 and HPZ2 have been combined and summarized in the experimental analysis, such as the failure load, the failure mechanism, the load at which the first inclined crack occurred, the cracking angles of the observed cracks, the calculated inclinations of the compression field from the LVDT measurements, the contribution of the shear reinforcement and the contribution of the prestressing cables to the shear capacity. Remarkably, the outcome of the test resulted in shear-compression/flexure-shear failure instead of the predicted shear-tension failure. The purpose of this thesis is to check whether the observed shear capacity and failure mode from HPZ1 and HPZ2 can be validated with existing models that are currently used by (inter)national standards and numerical programs. The Euler-Bernoulli beam theory and five (inter)national codes: ACI 318-14 (American Concrete Institute), AASHTO 8th Edition (American Association of State Highway and Transportation Officials), NEN-EN 1992-1-1:2011 (Eurocode 2), RBK 1.1:2013 (Richtlijnen Bestaande Kunstwerken) and EC2 draft 2018 (prEN 1992-1-1:2018 D3), have been used to calculate the shear capacity and if possible the failure mode of the Helperzoom girders. Next to the nominal shear resistance, failure of the compression field is considered for three codes: AASHTO, EC2 and EC2 draft 2018. For the two Eurocodes the value of the inclination of the compression field can be chosen by the user: the EC2 has a lower limit of theta = 21.8°, the lower limit of the EC2 draft 2018 (based on state of strains) is reached when theta is chosen such that failure of the compression field occurs simultaneously with yielding of the stirrups. For the EC2 draft 2018 different ways have been used to determine the longitudinal strain: with the expression given in the code, analytically determined with a sectional analysis and with the results of the LVDTs in the two experiments. In addition to the analytical calculations, a non-linear finite element program Response-2010 has been used, with which a cross-sectional analysis was made with two values for the prestressing force. With this program it is easy to determine the maximum shear capacity, the failure mechanism and many other results per loading step, such as the inclination theta, acting and maximum compressive- and tensile stresses, strains, etc. The maximum shear capacity is divided into components: the contribution of the uncracked concrete, cracked concrete, transverse reinforcement and a vertical prestressing force. Four different shear capacities have been calculated: the inclined cracking load, the nominal shear resistance according to the general procedures of the design codes, failure of the compression field and the moment that failure of the compression field occurs simultaneously with yielding of the stirrups. The Euler-Bernoulli beam theory, ACI (flexure-shear) and Response-2010 show that the load for the first inclined crack are close to the results of HPZ1 and HPZ2. For the nominal shear capacity, none of the codes nor Response-2010 are in line with the results of the two tests: all shear capacities are underestimated. The AASHTO overestimates the shear capacity for failure of the compression field, because the inclination theta is not included in the expression. The EC2 overestimates failure of the compression field due to limitation of theta = 21.8°. The EC2 draft 2018 allows for lower values for theta, when the longitudinal strains are based on the state of strains with theta lower than 19.08°. The results for the shear capacity and inclination of the compression field of the latter design code are much more in line with the observed failure loads and inclinations calculated from the LVDTs. The lower limit for the shear capacity is when failure of the compression field occurs simultaneously with yielding of the stirrups. With this limit, the shear capacity is underestimated and the inclination of the compression field is lower than the inclination calculated from the LVDTs. The results between the three analyses have been compared with each other and it was concluded that there are major differences between the analyses for the calculated shear capacities, internal lever arms, critical positions and the inclinations of the compression field. None of the results from the codes match the observed failure load in the experiments. Considering the expressions given for failure of the compression field, the EC draft 2018 based on the state of strains were closest to the test results for both the shear capacity and the calculated inclinations of the compression field from the LVDTs. The moment that yielding of the stirrups occurs simultaneously with failure of the compression field, the EC2 draft 2018 gave too low values for the shear capacity. For the numerical results, Response-2010 gave a representative shear force for the first inclined crack and failure mechanism, but not for the ultimate shear capacity. After the onset of the first inclined crack, the girder did not build up extra capacity as was observed in the experiments. The critical position was also not in line with the results from the test. It can be concluded that the results should always be looked at from a critical point of view and that no clear answer can be given as to which analysis is the "best" to determine the shear capacity of (prestressed) concrete T-girders. For the Helperzoom girders the EC2 draft 2018 based on the state of strains with theta lower than 19.08° gave the best results for the shear capacity.

With the rising demand for renewable energy sources the amount of wind turbines which are built on land are growing rapidly. Because of the repetitive nature of the foundation small design improvements can add up to large savings in material usage and building cost. The most critical part of the foundation is the connection between the metal mast and the concrete foundation. This connection is made by implementing an anchor cage. The application of an anchor cage results in complex multiaxial stresses in the surrounding area. Confinement plays a large role in the compressive strength of the concrete subjected to the partially loaded area created by the anchor flange. The main goal of this thesis is investigating the best way of modelling the concrete surrounding the anchor cage at confinement levels being present in the wind turbine foundation. This is done by investigating the theory regarding confinement and the effects of it. But also the way this is captured by analytical models. To make a comparison between DIANA and the analytical models the present stress situation in the wind turbine foundation is analysed. Looking at the stress distribution and the confinement levels. Next a comparison of the ideal case of confinement is made. This is later expanded to a larger scale model, to compare the effects of confinement. The confinement present will enhance the concrete strength and strain properties. The concrete specimen can resist larger loads and reacts more ductile. These properties are captured in analytical confinement models, these are compared to the way DIANA approaches confinement. The anchor rods between the anchor flanges are prestressed, this prestressing results in a permanent stress situation. Within this stress situation there is a small part beneath the anchor flange subjected to confinement. With increasing pressure, originating from the moment load which results from the wind on the tower and it’s blades, the confined area increases to the top half of the foundation. With significant confinement in the pedestal. Comparing the DIANA compressive behaviour models with the analytical confinement models and experimental data within a one element model. It is seen that compressive behaviour models do react on the confinement. Although they show a lower peak strength than the analytical models. A larger difference is noted in the underestimation of the peak strain. This difference in outcomes is the result of the different approaches between DIANA and the analytical models. As well as some assumptions that DIANA makes concerning the strength and strain increase factor. The Parabolic compressive curve is most suitable for modelling the confinement in this ideal case. A case study is conducted to further investigate how the confinement is represented in a total non-linear model. Modelling the top part of the foundation and checking the effect that confinement has on this model. For this model the prestressing of the anchor rods is increased until failure. Without confinement the concrete elements directly beneath the anchor flange fail in compression. Running the model with confinement it is noticed that the underlying weaker concrete is failing in compression first. This is the result of the confinement being present surrounding the anchor flange. The model with confinement is also able to resist a 30% larger load than the model without confinement. The parabolic compression curve is the most suitable curve currently available inside the strain based crack model for modelling the effects of confinement. Overall DIANA is able to capture the effects of confinement well enough to see the positive effects in the case study. Due to limitations in the analyses performed and in their interpretations, it is not possible to give an unequivocal answer on the effect of confinement within the foundation of the wind turbine.

Load Testing of Bridges, featuring contributions from almost fifty authors from around the world across two interrelated volumes, deals with the practical aspects, the scientific developments, and the international views on the topic of load testing of bridges. Volume 12, Load Testing of Bridges: Current practice and Diagnostic Load Testing, starts with a background to bridge load testing, including the historical perspectives and evolutions, and the current codes and guidelines that are governing in countries around the world. The second part of the book deals with preparation, execution, and post-processing of load tests on bridges. The third part focuses on diagnostic load testing of bridges. This work will be of interest to researchers and academics in the field of civil/structural engineering, practicing engineers and road authorities worldwide.@en

Load testing of concrete bridges is a practice with a long history. Historically, and particularly before the unification of design and construction practices through codes, load testing was performed to show the travelling public that a newly built bridge was safe for use. Nowadays, with the aging infrastructure and increasing loads in developed countries, load testing is performed mostly for existing structures either as diagnostic or proof tests. For newly built bridges, diagnostic load testing may be required as a verification of design assumptions, particularly for atypical bridge materials, designs, or geometries. For existing bridges, diagnostic load testing may be used to improve analysis assumptions such as composite action between girders and deck, and contribution of parapets and other nonstructural members to stiffness. Proof load testing may be used to demonstrate that a structure can carry a given load when there are doubts with regard to the effect of material degradation, or when sufficient information about the structure is lacking to carry out an analytical assessment.@en