The shear capacity of concrete members is a major challenge of structural concrete research through the years. Many theoretical models have been developed and various experiments have been performed, focusing on the accurate prediction of the shear behavior. Many of the available theoretical models assume that a large contribution of the shear capacity is transferred through cracks by a mechanism often recognized as aggregate interlock. At the same time, due to the increase in the complexity of the structures and the development of the concrete technology, the mechanical properties of concrete have improved significantly. This fact leads to the need for modification of the existing models or the development of new ones, accommodated to the improved materials. Since, the aggregate interlock plays a significant role in the development of the shear capacity, the present research proposes a new numerical methodology for the calculation of the aggregate interlock in high strength concrete in which aggregates break, based on the widely recognized model proposed by Walraven and the results of direct surface roughness measurements. The crack surfaces of concrete cylindrical specimens drilled from a 70 years old existing concrete bridge and newly casted cubic specimens generated by splitting tensile tests were measured by a laser scanner. Moreover, the surface of a reinforced deep beam after flexural shear failure was measured as well. The measured crack surfaces were used to implement the plasticity based aggregate interlock model proposed by Walraven with an algorithm which was validated with Walraven’s theoretical model, using a so-called mesostructural model. The output of the analysis gave suggestions on the adjustment of the available aggregate interlock model for high strength concrete. The proposed model is then implemented into a shear test on a 1.2 m concrete beam, which has a concrete strength larger than 70 MPa and the aggregate interlock seems to influence significantly the shear resistance of a cracked section. Based on the observation of the surface roughness of a crack, the thesis further proposed that with a sufficiently large crack face, the localized variation in the crack surface is averaged out. Thus, the surface can be used to develop a master curve for the given concrete type. In the last part of the study, two improvement suggestions are given regarding the Critical Shear Displacement Theory. The one point is relevant to the simplification of the crack profile that can be changed from a straight line into a more inclined and the second point is related to the correction factor considering the fracture of the aggregates, that should be dependent on the crack width.

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.

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.

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.

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 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.

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.

In the Netherlands, there are generally two categories of structural forensic investigations. The first category are extensive investigations with the goal to learn from failure by investigating all aspects: technical, human and organisational. The second category are investigations that focus mainly on technical causes and the investigation goal is often determining the failure cause including designing repair measures. For this category, little information is available on used investigation processes.

In literature, several investigation methodologies have been described. However, they often describe only a very general process or on the other hand very specific material related laboratory tests. Descriptions and recommended techniques on how to perform the proposed steps of an investigation are scarce. To a client ordering a damage investigation, the most important parts of the investigation are the conclusion and the recommendations. The client expects that the conclusion is correct. Therefore, it is important to ensure that the used investigation process results in a reliable (consistently good quality and able to be trusted) outcome. Basic knowledge of bias may help to indicate possible threats to the reliability of investigations. Techniques used to increase the validity and reliability of case study research can assist in developing strategies to achieve reliable forensic structural investigations. Therefore, the question of this research is: what is a reliable methodology to perform investigations into the technical cause of damages to concrete structures?

The research question has been answered by studying available literature on structural forensic investigation techniques, interviewing investigators, researching investigation techniques used for aerospace accident investigations and fire cause determination, studying human error theory and case study research and concrete damage mechanisms.

Based on the resulting information from studying all these disciplines the conclusion can be drawn that using a structured investigation process is essential. Therefore, this information has been used to develop an investigation methodology called the ‘investigation process model’. The model recommends the following phases: orientation, data collection, hypothesis generation, hypothesis analysis, conclusion, reporting and follow-up. These phases are split into individual steps that guide the investigator through the process. Each step contains suggestions for specific techniques varying from taking meaningful photographs on location to using a standard layout for reporting in order to execute the step properly. The investigator can select the most appropriate techniques for the project. Special attention has been paid to provide techniques to generate and analyse hypotheses in a reliable way. An example is the tool ‘Concrete Damage Handbook’ to assist the investigator in linking visual damages to possible causes. As a common thread through the model measures have been provided to limit the negative influence of bias (based on the Delft approach).

Validation of the model with 1) a test case based on a real damage file, 2) comparison with real investigation reports and 3) scientific papers proved that the model relates to the daily working practice and is usable, practical and functional within the scope of the defined criteria.

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.

A series of accelerated corrosion tests were done by SGS INTRON (commenced by Combinatie Aanpak Maastunnel, constructor of the Maastunnel project) to investigate for a proper repair material for the deteriorated concrete floor in the Maastunnel at Rotterdam. Five types of fiber reinforced mixtures with different tensile behavior ranging from SHCC (strain-hardening cementitious composite) to ON06 (similar tensile behavior as normal concrete) were designed. Different cracking behavior was observed due to the different tensile behavior in the repair mortar. It is of utmost importance to investigate if the cracking behavior can be simulated by numerical modeling and if in the future, the parametric analysis might be performed without large experimental series.

Two types of numerical models are implemented in this master thesis, namely the lattice model and the continuum model. The lattice model can simulate the crack pattern of different materials in the accelerated corrosion test. The continuum model cannot show the behavior of decreasing number of cracks with decreasing fracture energy in the strain-softening materials due to the bifurcation problem brought by its incremental solution method. However, the lattice model shows the trend to underestimate the crack width of the strain-softening material. The continuum model has better performance in predicting the crack width. Also, the lattice model can predict the influence of the repair mortar-substrate bond strength on the crack pattern. Meanwhile, the continuum model always shows a complete failure in the repair mortar-substrate interface.
The boundary conditions at the bottom edge are observed to influence the direction of the bottom cracks. The edges of the specimen are kept free in the experiment. However, the repaired area is constrained by the surrounding concrete in reality. This indicates that the laboratory test may not represent the cracking behavior of the concrete floor in the tunnel accurately. SHCC is observed to be more sensitive to the repair mortar-substrate bond strength than material with lower stain capacity. Extra caution on the bond quality is advised while applying SHCC in a concrete repair system.

From the material point of view, with increasing fracture energy and strain capacity, more but thinner cracks can be performed in the accelerated corrosion test. SHCC material can perform the distributed crack pattern with a maximum crack width of 0.1mm which is ten times smaller than normal concrete. This behavior of SHCC is very suitable for being applied to a concrete repair system. The distributed cracks with smaller crack width can effectively limit the possibility of further corrosion. Besides SHCC, some strain-softening (under direct tension) materials can also show the deflection-hardening behavior in the bending test and produce the distributed crack pattern. SHCC and fiber reinforced concrete with deflection-hardening behavior in the bending test are suggested to be used in the concrete repair system.

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.

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.

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. . . .

Ordinary Portland Cement (OPC) consumption has grown nearly exponentially in the last twenty years. OPC has become the highest-volume manufactured product on the planet. Production of OPC is energy-intensive, consumes unrenewable natural resources and is one of the primary contributors to global warming (accounting for at least 5-8% of worldwide anthropogenic CO2 emissions). An alternative for OPC concrete is Alkali-Activated Concrete (AAC), for which Portland cement is completely substituted by an alternative binder. Instead of using OPC and water, precursors (raw materials) like Blast Furnace Slag (BFS) or Fly Ash (FA) are activated with an alkaline activator solution.
Although AAC seems to have promising qualities for structural application in terms of sustainability, worldwide use is not yet established. One of the reasons for this is the fact that there are no available regulations or codes to apply it, the material is relatively new and limited research has been conducted. For OPC concrete, the design codes are based on compressive strength at 28 days (strength at later ages stays either constant or is higher) and most other mechanical properties used in calculations are estimated based on this compressive strength. For AAC it is not yet sure if the same relations and assumptions as for OPC are also valid. First, because mechanical properties that have been reported for AAC in literature vary a lot, depending on mixture composition and curing conditions. Second, the long-term strength development of AAC is scarcely investigated and it is not clear if the compressive strength at 28 days can be used as a safe reference for design. Namely, a few researchers reported a decrease of strength or stiffness over time, for AAC mixtures that contain blast furnace slag. The observed decrease might not be a very desirable phenomenon and should be well-understood prior to wider structural application of AAC. Therefore, the main research question of this thesis is: Can a decrease of stiffness and strength over time, as sometimes reported in literature for AAC, also be found for AAC used at TU Delft and if so, what could be an explanation for this behaviour? Does the amount of BFS in the binder play a role, as a decrease over time has only been reported for AAC containing BFS? And if not, what other cause could lead to a decrease of properties over time? The intention is to make some first steps towards a better understanding of this phenomenon.
The research question is investigated in an experimental manner. Compressive strength, elastic modulus, splitting tensile strength and flexural strength are tested at different ages (28, 56 and 91 days) after being wet-cured (20°C and 95% RH) for 28 days. Two different AAC mixtures are investigated, S100 and S50, characterized by a BFS/FA binder ratio of 100:0 and 50:50 respectively. Furthermore, the flexural behaviour of reinforced beams is investigated by conducting four-point bending tests on both S100 and S50 concrete of two different ages (33/34 days and 69/70 days) and compared to an OPC concrete control beam.

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.

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.