In the construction of subsoil structures, a common challenge is the presence of a high groundwater level in combination with the absence of a naturally impermeable layer or an environment susceptible to settlements due to lowering the groundwater level. To overcome this issue, a building pit with an underwater concrete floor (UCF) can be constructed. The UCF ensures structural rigidity and allows for the building pit to be drained such that a dry and safe subsoil construction site is obtained. The objective of this thesis is to investigate how design efficiency of underwater concrete floors can be improved. In an effort to reduce material usage and achieve cost-effective structures, the following research question was stated: “What is the influence of design parameters and how can parameters be adjusted to improve design efficiency of an underwater concrete floor, and to what extent can the addition of fibre reinforcement contribute to this optimization?” A parametric model was developed to provide insight to the sensitivity of parameters and their impact on design resistance. Furthermore, the model was utilized to examine under what circumstances potential material savings can be obtained by implementing fibre reinforced concrete in UCF’s. This was accomplished through the evaluation and comparison of the minimum required thickness based on bending moment resistance in various scenarios, for both UCF’s and steel fibre reinforced UCF’s (SFUCF). Results obtained with the parametric model established that, in order to enhance the bending moment resistance of an uncracked UCF, increasing the nominal thickness becomes relatively more effective compared to increasing the concrete strength class for higher normal forces. When utilizing a compression arch to obtain bending moment resistance, the implementation of ribbed tensile elements or an increase in nominal thickness are found to be the most suitable methods for increasing resistance. For enhanced shear force resistance, increasing the nominal thickness over the concrete class provides relatively more additional resistance for slender UCF’s. The results found that through the application of ribbed piles, most punching shear force resistance can be obtained. Three use cases for a SFUCF were identified using the parametric model. When centre to centre (c.t.c.) distances larger than 4.4m are applied in combination with a substantial normal force, significant material savings of up to 0.3m thickness are possible, which equates to a reduction of material usage by 30%. For situations where the effective height of the compression arch is small, it was also found that material usage could be reduced by 30%. Perhaps the most significant use case for a SFUCF is when the normal force is close to zero, and additional normal force cannot be obtained through membrane action. In these situations, the application of a SFUCF can make an otherwise near impossible project feasible. As a new design approach, a cost-based optimization tool was developed using the parametric model. An already executed UCF was evaluated using the tool, it was determined that a more cost-effective design could have been achieved, with potential savings of up to 30% in costs.

New and existing bridges in the Netherlands must abide by structural safety codes, such as the Eurocode. In this code, structural safety is expressed through the reliability index 훽. For certain reference periods a threshold value for 훽 exists. When applying prescribed load models given in the Eurocode, the structure is guaranteed to at least fulfil to this threshold value. However, these prescribed load models are deterministic in nature and can be rather conservative for bridges in urban areas. This thesis focusses on creating a probabilistic load model based on actual traffic loading by making use of a camera system that registers license plates to check whether the vehicle is allowed to enter the inner city of Rotterdam due to environmental zones. From this camera system data, technical information such as wheelbase, legally allowed axle loads, gross vehicle weight and such can be extracted since they are coupled to license plates. This technical information is then used to create load models based on actual registered traffic. This load model represents trucks as point loads with interspatial axle distances. In total, one year of collected data by the camera system is stored, called the LP data. This load model is then used in a probabilistic reliability analysis as a load variable input. When comparing the LP data with available weigh-in-motion (WIM) data from two measurement locations in Rotterdam, it turned out that the LP data does not incorporate under- and overloaded axles and was overestimating the accompanying reliability index. Hence to account for this, an axle load factor 휂௜ is introduced to simulate under- and overloaded axles. This factor 휂௜ is based on the WIM data and is different for each vehicle type. With the use of this factor, a second, improved load model is constructed. This is referred to as the modified LP data. A third and final load model was constructed from the available WIM data, called the WIM model. For each of these three load models the load effects were calculated, and distributions were fitted accordingly for simulating several 25 year periods of traffic. The output of these load models is a loadeffect maxima distribution that can serve as a direct input in a probabilistic reliability analysis. With these three load models, a hypothetical slab with a span length of 10 m was probabilistically analysed where the LP model, the modified LP model and the WIM model resulted in reliability indexes of 4.8, 4.1 and 3.7 respectively. When compared to the requirement in the Eurocode, all load models comply. Concluding from this, the modified LP model suggested in this thesis can be used as a load input in a probabilistic verification for this very considered bridge location. For this load model to be applicable to multiple bridges, more research must be done since only one location was considered in this thesis. However, the suggested approach to construct load models based on license plates can be used verify the applicability to multiple bridges.

During construction in urban areas often noise and vibrations are not tolerated. For the installation of the foundation piles in these cases there is often chosen for screwed displacement piles. These piles can be installed without nuisance for the vicinity, but do induce large soil displacements during installation. The soil displacements can cause increased soil pressure on adjacent structures. Because urban areas are getting more densely built, these problems will occur more often in the future. The effects can be minimilized when they are known in advanced. This research looks into the possibility of predicting the installation effects of screwed displacements piles on adjacent structures. This is divided in the prediction of the soil displacement in a finite element analysis and in the effect of the soil displacement on adjacent piles. This is done with two case studies. First data from tests in Shanghai is used to create a finite element model. After this measurements are done in Rotterdam to verify this model for Dutch cases. Combining all the analysis of the measured and modelled displacements showed that the displacement is depended on the stiffness of the soil layers, the initial displacement at the edge of the pile and the distance from the pile. The soil parameters influence the initial displacements in each soil layers. When the initial displacements are correctly determined with tests, it is possible to predict the soil displacement due to the installation of a screw pile with a finite element model. No conclusion could be made on the effect of the soil displacements on adjacent structures.

Areas are getting more and more populated causing new infrastructure lines to be constructed below the surface. A bored tunnel is one of the possibilities to create this subsurface infrastructure, but the construction process of a bored tunnel is a complicated one. Many loads and aspects are present in this construction process that can be divided into six phases. In each of these phases, different loads and aspects are acting on the tunnel lining or the surrounding soil which can cause the lining to deform. The increasing complexity and demands of problems have led to the use of the finite element method. A computer based method which allows one to model the problem. For finite element modelling, numerous programs are available of which several claim to be able to model bored tunnels. However, it is not yet clear what the exact differences between the different programs are. With many aspects to be modelled, many differences between programs occur, either in the soil, the tunnel lining or a combination of both. This research has focussed on the possibilities of modelling the different construction phases of bored tunnels in two widely used programs: DIANA and Plaxis. Simple two dimensional (2D) models were created to which the different construction phases were added before continuing with three dimensional (3D) modelling. This approach has led to a good assessment of the possibilities and limitations within these two programs. DIANA is not yet suitable for modelling the construction process of bored tunnels completely. The construction phases are modelled undrained to account for the relative short time they are acting. A consolidation phase in which the pore pressure can dissipate cannot be modelled in DIANA, which is essential for modelling the construction phases. Plaxis, on the contrary, is not able to model joints in the segmental lining appropriate for 3D. In 3D, Plaxis only allows to model a joints as "fixed" or "free". In DIANA different theories can be applied to the joints, including Janssens. For 2D, both programs have a rotational springs besides the free and fixed connection for modelling the joints. For the model in which the material models were changed, the difference with the main impact between the two programs occurred, especially for the bending moment. This means the Modified Mohr-Colomb material model in DIANA is different than the Hardening Soil model in Plaxis. Including the construction phases leads to more favourable internal lining forces for tunnels, something of which clients should be convinced. However, not until the models have been benchmarked with measured data from a tunnel project. While 3D models have been investigated in this research, they should be extended in order have a better understanding of the different 3D phenomena that are present in the construction of bored tunnels. This will both assess the possibilities of modelling this process and more potential differences between programs can be investigated. Besides extending the 3D models, other programs should be investigated on their capabilities too. In order to come to a proper assessment of the possibilities, program experience is strongly recommended. These programs should also be compared with measured data for benchmark purposes.

Compressive membrane action is a phenomenon commonly found in reinforced concrete structures after significant cracking and deformation have taken place. In this thesis report, the potential benefit of CMA in immersed tubes subjected to fires is quantified through a finite element study. Furthermore, sensitivity studies are conducted in order to determine the boundary conditions necessary in immersed tubes to induce CMA.

Recently experiments were conducted at the Technical University of Delft on the size effect of concrete. The size effect is a term used for the relative decrease in shear capacity with an increase in height of the structural member. The beams observed in the experiment failed much sooner than was predicted. These test results have implications for the Heinenoordtunnel, the roof of which shares many of the characteristics of the beams that were used in the experiments. The question is posed what happens to the Heinenoordtunnel in case of a fire, when also considering the recent tests on the size effect of concrete. The Heinenoordtunnel is analysed with a numerical model. First however, in order to account for the observed size effect, the beams from the experiment are recreated. A study is performed on the effect of various parameters on the numerically obtained failure load, cracking load, crack pattern and deflection in order to find a set of parameters to approximate the observed size effect. It was found that a significant reduction in tensile strength and fracture energy is necessary to obtain a better approximation of the experimental results. However, despite these changes the numerical model still overestimates the shear capacity. This information is used to create a model of the Heinenoordtunnel. A situation without a fire load is analysed and validated. The model is compared with the analytical IBBC-TNO method. Consequently, the model is subjected to a fire load. The fire is modelled using temperature dependent properties and by determining the temperature ingress for a 2 hour RWS fire. A significant shear crack is found present due the fire load, the location and shape of the crack suggesting onset of shear compression failure. The model however is still considered to be in equilibrium and so failure has not actually occurred in the model. A comparison with an analytical model suggests that a shift in bending moments from the increase in temperature results in a shift of shear capacity in the roof. It is concluded that, while the numerical model does not fail, some caution is advised for the translation of these results to practical application. The change of material parameters found in modelling the size effect tests still leads to an overestimation of the shear capacity. On the other hand, the situation that was modelled was an extremity. In the model of the Heinenoordtunnel the absolute physical maximum water load was assumed in conjunction with an extreme fire. It is recommended to check the fire load with computational fluid dynamics modelling, to see if the fire load could possibly be less severe than assumed.

Het Noordzeekanaal verbindt de Haven van Amsterdam met de Noordzee via het sluizencomplex van IJmuiden. In de huidige situatie is de Noordersluis maatgevend voor de maximale diepgang van de scheepvaart op het Noordzeekanaal. Met de geplande realisatie van Zeesluis IJmuiden begin 2022, zal de Noordersluis niet langer maatgevend zijn voor de maximale diepgang. In de nieuwe situatie zal de bodemligging van het Noordzeekanaal maatgevend zijn voor de maximale diepgang van de scheepvaart. Het Centraal Nautisch Beheer en Rijkswaterstaat wensen de scheepvaart capaciteit van het Noordzeekanaal te bepalen afhankelijk van de beschikbare waterdiepte en de daarbij passende diepgang van schepen. Uit eerdere onderzoeken bleek de Velserspoortunnel maatgevend te zijn bij eventuele verdieping van het Noordzeekanaal. Daarnaast werd geconcludeerd dat de spoortunnel in de huidige situatie niet voldoet aan de eisen omtrent de minimale tunneldekking. Verder bleek de dynamische kielspeling boven meerdere Noordzeekanaal tunnels te klein te zijn. Tevens werd duidelijk dat door de optredende bodemsnelheden, veroorzaakt door schroefwerking en retourstroom, de kritische snelheid van de tunneldekking overschreden wordt. Aangezien de constructieve veiligheid van de tunnels gelegen onder het Noordzeekanaal niet in het geding mag komen dient meer inzicht te worden verkregen in de veiligheid van de tunnels bij scheepvaart calamiteiten. De rol van de dekking op de tunnels is hierbij cruciaal. In het onderzoek is daarom ingegaan op de optimalisatie van de tunneldekking bij scheepvaart calamiteiten. Aan de hand van literatuuronderzoek is inzicht verkregen in de scheepvaart calamiteiten. Vervolgens is de verkregen kennis toegepast op de casus van de Velsertunnels, door de tunnels te toetsen aan de vereiste veiligheid bij de calamiteitsbelastingen. Tot slot zijn alternatieve tunnelbeschermingen onderzocht voor de Velsertunnels waarbij het meest geschikte type bescherming verder is uitgewerkt.

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.

Watertightness and leakage prevention is crucial in every tunnel joint design. Immersed tunnels have been utilizing the Gina-Omega gasket solution since the 1960s to prevent leakage from occurring. However, after almost 50 years of service life, leakages were detected in the immersion joints, which leads to an investigation into the source of the problem. It was uncovered that the bolts of the Gina gaskets had failed due to the immense load exerted by the sand above them. It was apparent that the load on the gaskets builds up due to an increase in soil stresses. A hypothesis was formed regarding this phenomenon; the sand inside the joint gap was exposed to almost 50 years of loading and unloading cycles from the expansion and contraction of the tunnel elements due to seasonal changes in temperature. This, in turn, densifies the sand inside the joint gap, which results in rising soil stresses. A 1:3 scaled physical model of the joint gap was designed and constructed to test the validity of this hypothesis. The model joint gap is equipped with a static lining on one end and an actuated lining on the other, hence the device is able to imitate the annual joint contraction and expansion cycle. A barrel containing sand is fixed onto the top of the model joint gap and acts as a reservoir of sand, allowing for more sand to enter the joint gap. The device is also equipped with 2 load cells and an LVDT, which allows for the measurement of horizontal soil stresses and vertical gasket displacement respectively. Two holes, with a flap covering each of them, are installed on the side of the model joint gap, which allows for a penetrometer test to be conducted on the joint gap sand. Multiple experiments with varying configurations and test conditions were performed. The results show that although the multiple loading and unloading cycles apply the same displacement for every cycle, the soil stresses increase with time. The Gina gasket show an apparent “walking effect,” where the gasket moves continually inwards. While a similar test conducted without the presence of sand fails to produce any “walking effect.” Penetrometer measurements show that the soil increases in density over time. The investigation is continued further with finite element analysis using the geotechnical modeling software PLAXIS. The joint gap part of the device is modeled in the program and is subjected to loading conditions and configuration similar to the physical model. Results of the simulation show indications of gasket “walking effect,” as well as stress-strain behavior similar to the experiment results. A comparison analysis between the results of the physical and finite element model is subsequently conducted. The finite element analysis allows for the calculation of the sand vertical stresses, which is previously unable to be measured during the experiment. It is observed that the vertical stresses rapidly escalates due to the high friction between the sand and the lining wall. A further analysis is conducted to estimate the force required to push back the displaced Gina gasket. Due to the good agreement between the results of the physical and finite element models, a modified version of the finite element model is used to predict the resulting pushing-back forces. Finally, the research is concluded with the validity of the previous-mentioned hypothesis. It was also confirmed that the soil undergoes densification, proven by the penetrometer readings as well as further validated by the stress-strain behavior of the sand. It is also proven that at higher horizontal strain, the increase in density, stresses, and the “waking effect” is more pronounced. The force analysis produces values of force needed to push back the Gina gasket. It was concluded that pushing back the entire Gina gasket upwards would require a high amount of force. However, affecting only 1/3 of the gasket bottom area would result in the gasket merely being pushed aside while failing to push the soil upwards.

Strain Hardening Cementitious Composite (SHCC) is a new type of concrete that is able to control the crack-width in concrete structures. The application of this material in the tension zone of hybrid concrete structures is thus of interest in practice. The interfacial behavior for these hybrid structures is something that is of importance for the composite action. Therefore, a study is performed to investigate the behavior of the interface in hybrid SHCC-concrete beams. This is done by performing an experimental study on beams with a joint at midspan. Several parameters such as the interface roughness, coupling reinforcement cover, curing method and protruding reinforcement have been investigated. The hybrid SHCC-concrete beams are tested in a four-point bending configuration to obtain a constant-bending moment region along the interface. The crack propagation along the interface and through the SHCC/concrete has been evaluated with the use of Digital Image Correlation (DIC). Furthermore, also a numerical analysis has been performed using DIANA FEA based. The numerical analysis was used to help to determine the experimental campaign. Furthermore, also several experimental samples have been modelled to study the behavior of the beam in more detail and to make recommendations for future modelling of the interface. Based on the experimental results, the influence of the interface roughness resulted in an increased bond at the interface. This is both seen in an increased bearing capacity and a reduction of the interface and joint opening at equal loads. The profiled interface and holed interface resulted in an increased capacity due to the mechanical interlocking at the interface. The bearing capacity of these samples increased by 78.4% and 54.7% respectively compared to the reference sample (13.9 kN). In case of the profiled sample, no delamination of the interface occurred as the sample failed due to a horizontal crack at the level of the coupling reinforcement. This can be attributed to the localized tensile stresses at the reinforcement level. The last sample with a different interface roughness consisted of epoxy and sand (1-2 mm). For this sample, the bearing capacity increased by 51.8%. The failure of this sample was a combination of interface delamination (initially at the joint) and a horizontal crack through the coupling reinforcement. For all the samples with a different interface roughness, no yielding of the coupling reinforcement occurred. Several beams with a smooth interface have also been tested by adjusting the reinforcement cover, curing method and applying protruding reinforcement. The influence of the reinforcement cover didn’t have an effect on the bearing capacity. However, the interface and joint opening reduced significantly as the eccentricity of the reinforcement bars also reduced. Furthermore, also the effective height increased resulting in lower reinforcement stresses. The influence of a different curing method was investigated by placing the sample in a humidity-controlled (50 %) room to investigate the effect of shrinkage. The results showed that the bearing capacity remained similar to the reference samples. This can be attributed to the fact that the bond internally was still good, caused by the restraint of the reinforcement bars. However, the deflection of the beam increased as a result of the reduced stiffness by the shrinkage induced cracks. Finally, one sample consisted of stirrups at a distance of 50 mm from the joint to take up the tensile stresses at the interface (e.g. due to reinforcement eccentricity). The results showed an increase in bearing capacity by 102.7% compared to the reference sample. However, also in this case, no yielding of the coupling reinforcement occurred. The failure of the sample is also caused by the delamination of the interface. Furthermore, as a result of this delamination, fracture of the top part of the SHCC occurred at the location of the protruding reinforcement due to the rotational restraint of the stirrup. The 2nd part of the study consisted of a numerical analysis. A Coulomb-friction model with an interface tensile strength cut-off is used to model the interface. Based on this, a good correspondence between the experimental results and FE results is found in terms of the bearing capacity and failure mode for the sample with a smooth interface(delamination). However, the crack propagation of the flexural cracks through the concrete and SHCC was substantially different. The sample with a profiled interface has also been modelled in Diana FEA. This is done by implementing the profiled interface manually in the FE model. The model showed a good correspondence with the experimental results in terms of bearing capacity and interface and joint opening. The crack propagation in the concrete is also similar to the experimental results. The model however doesn’t show any flexural cracking in the SHCC layer as a result of the limitation of DIANA FEA. Also, an additional study is done to replicate the behavior of this beam using a smooth interface. Based on this model, it is recommended to use a perfect bond at the interface. For both these models, the FE model wasn’t able to replicate the strain hardening behavior of SHCC. This is due to the limiting material models in DIANA.

Underground infrastructures and the importance of the people’s safety and structures robustness are relevant and contemporary issues in the civil engineering industry. The demand for this infrastructural typology has developed to such an extent that the need for a better and cost-beneficial knowledge of the risks is necessary. This thesis aims at bridging and developing further the knowledge on Fire safety engineering and structural engineering on the particular topic of spalling failure. Another objective of this thesis is the discussion over the possible replacement of the used procedures used to assess and guarantee tunnel safety. Both from a fire safety and structural engineering point of view, prescriptive measures and solutions are mostly proposed to accomplish a safe tunnel design. This causes the design to be non optimised and in some cases more costly than what is actually needed. From the fire safety side, the use of pre-given fire curves is put under discussion. Research has been conducted to asses which are the origins of the most widely used curves. Studies have also been performed to develop a practical analytical engineering method to analyse and estimate the consequences of a given fire scenario tailored to the specific tunnel under consideration. Subsequently the results of the analytical models have been compared with the results obtained with advanced Computational Fluid Dynamics tools. Finally, more complicated scenarios have been studied with the use of this software. On the other hand, from a structural engineering point of view, a new model able to describe the spalling mechanism has been proposed. The model predicts the spalling time for NSC elements and at the same time verifies which is the optimal thickness for the piece to spall. On top of that the possibilities for further use of the model in the description of the spalling mechanism for HSC and PPFRC elements have been investigated. Finally this two topics have been combined together and conclusion have been drawn.

Starting from the late eighties induced seismic activity is present in the Northern part of the Netherlands. Cause of these earthquakes is the extraction of natural gas. In this region, most of the building stock comprises out of unreinforced masonry (URM) buildings. Multiple experimental campaigns are performed since 2014 to investigate the structural integrity of these type of structures. Both static and dynamic, full-scale and smallscale, experiments are executed to identify both in-plane and out-of-plane failure mechanisms. Strengthening, or retrofitting, of these already existing structures, is of interest and different researchers propose multiple techniques. From the literature, it is found that the application of strain hardening cementitious composites (SHCC) results in the required improved structural performance of the retrofitted masonry. The SHCC material is characterised by high ductility in the range of 3-7%, tight crack widths of around 60 μm and a relatively low fibre content equal to 2% (maximum by volume). In this experimental campaign small-scale, both inplane and out-of-plane (i.e. shear strength and flexural strength, respectively), experiments are performed on masonry samples retrofitted using a single-sided applied SHCC overlay. Different thicknesses of this overlay, masonry surface preparations, and overlay curing conditions are considered. With the help of these experiments the material properties of retrofitted masonry are investigated. From the initial shear strength experiments, it is concluded that the retrofitting approach did not work as intended. Results of all the different specimen examined shows similar capacities to the non-retrofitted masonry triplets. With the help of digital image correlation, it is shown that for all of the retrofitted specimen, the overlay material is not activated during the tests. Additional experiments and numerical simulations are performed to investigate the several parameters possibly influencing these experiments. The bond strength of the interface between the SHCC and the masonry substrate is determined to be too low. This is one of the main factors resulting in the absence of cracks in the retrofitting overlay. Additionally, the high cracking strength of the SHCC mixture considered, and the applied pre-compression, have influenced the cracking behaviour of the retrofitting overlay. Besides the shear strength of the retrofitted masonry material also the flexural strength is investigated with multiple out-of-plane four-point bending tests. Retrofitted masonry beams are used for these experiments. The plain masonry beams are not able to carry their self-weight, therefore all of the additional capacity is accommodated to the applied overlay. The experimental results are governed by shear failure. For eight out of ten specimens debonding of the masonry units is prevalent. Two of the retrofitted masonry beams showed flexural failure. A thicker overlay will result in higher flexural strength. Again, the bond strength between the overlay and the masonry substrate seems to be governing. No numerical analyses are performed to analyse these experiments in more detail. From this research, it is concluded that a single-sided SHCC overlay can be a very attractive method for retrofitting unreinforced masonry. However, both the interfacial bond strength and the material properties of the SHCC material must be taken into account. The bond strength must be sufficiently high, and the cracking strength of the overlay material sufficiently low, for the overlay to be activated. With the help of numerical simplified micro-models, the requirements of both parameters can be estimated.

Conventional building methods are still based on the reinforced concrete industry. In the last decades, timber has become more popular because it could be a more sustainable alternative. However, pure timber is not always an option, especially when slender design is required by the client. Because of its low elastic modulus, deflections often require an increased deck height. Therefore, this research focuses on the strengthening of timber bridge decks with reinforcement and prestress in order to increase their slenderness (= the ratio of the span to the height of the cross-section). This might make timber decks more competitive to reinforced concrete designs regarding slenderness. The problem is that prestressing timber decks will lead to creep deformations that induce losses of prestress force. This research is focused on modelling the creep deformations and the resulting resistance losses of prestressed timber decks. First, a cross-sectional model is developed to be able to find the initial resistance of a reinforced- and prestressed timber deck. This model is based on an incrementally increasing curvature so that the deck behaviour can be quantified from zero load to the failure load. Second, a time dependent model is developed to find the displacements and resistance through time. The timber bridge deck is modelled with ODE systems. The ODE's are used to find the (1) displacements and (2) strains of the deck. To obtain the time dependent behaviour of the deck, a viscoelastic E-modulus is substituted into the displacement- and strain equations. This viscoelastic E-modulus decreases with time, which causes an increase in displacements (= creep displacement). In the same way, the strains are modelled over time. The time dependent creep stains are implemented in the cross-sectional model to find the reduced resistance of the timber deck. The outcomes of the model suggest that large prestress forces lead to negative creep deflections (= creep in upwards direction). Meaning that for the right value of the prestress force, also zero creep deflections can be obtained. Besides creep, the instantaneous deflections are a large part of the total deflections. According to the results of the model, the instantaneous deflections can be decreased by up to 70%. Regarding the resistance, the final increase of bending moment resistance can reach up to 30% by incorporating prestress (at t = 50 years, including losses due to creep). Due to creep, prestress force is lost over time, resulting in a decreased deck resistance. This research shows that the creep losses result in a bending moment resistance decrease of up to 12%. Taking this into account, a bridge deck with a slenderness of 31 to 33 will be able fulfil its requirements after 50 years of service life. Depending on the client requirements, a slenderness of over 34 can be reached. Using Eurocode, creep deformations are calculated with a simplistic and conservative method. The model that is built in this research gives a more advanced way of determining the creep deformations of a timber deck. This leads to more realistic quantification of creep behaviour. However, Several factors still cause uncertainty in the model. Therefore, experiments with timber decks should be done to obtain more accurate data for the creep behaviour. The model from this research can be calibrated according to data from experiments, which will increase the reliability of the results.

A parking garage of Eindhoven airport partially collapsed in 2017. It was caused by failure of the longitudinal joint (long-side) of the composite plank floor or breedplaatvloer on the roof level. Experimental and numerical research showed that the joint suffered high positive bending moment in its transverse direction. However, from the investigation results, there was not enough resistance at the concrete-to-concrete interface around the joint to transfer the tensile force from the precast to the cast-in-situ section, which led to delamination of the two layers of concrete and resulting in failure when the delamination crack reaches the end of the coupling reinforcements. As happened in that case, the concrete-to-concrete interface usually is the weakest link and has a critical role on behaviour of a composite concrete system, especially the one which has unreinforced interface (no stirrup near joint). Further studies have been conducted to understand the influence of various details around the joint on the interface behaviour. In this thesis, details in spacing between lap splices (coupling reinforcements in cast-in-situ layer and bottom reinforcements in precast layer), spacing between connecting reinforcements (stirrups crossing the interface near the joint), the role of connecting reinforcement, and the sensitivity of interface parameters were studied numerically using DIANA finite element analysis software. Since the spacings are in direction of the specimen’s width, interface behaviour was analysed in both longitudinal and transverse directions. An additional study about compressive membrane action or arching was also conducted to understand the influence of lateral restraint, which usually occurs in composite plank floor systems used in buildings, including the one used in Eindhoven parking garage, to the capacity of the structure. This action was suspected of providing additional strength to the existing composite plank floor Two composite SHCC-concrete beam specimens from the experimental research by Harrass [1] were used in this numerical study since the experiment had both unreinforced and reinforced interface specimens which were important for this study. The unreinforced interface beam (Sample 1) was suitable for the study of lap splice spacing and lateral restraint without any influence from reinforcement crossing the interface, while the reinforced interface beam (Sample 7) was suitable for the study of stirrups spacing. The specimens are solid beams (without weight-saving element) consisting of a SHCC (Strain Hardening Cementitious Concrete) precast layer with a joint in the mid-span, and a regular concrete cast-in-situ layer. By using DIANA 10.4 finite element analysis software, this study is able to simulate both specimens in 2D and 3D numerical models. The models represented Sample 1 failed with a horizontal crack along the interface and a flexural crack at the end of coupling reinforcement reaches the top of the cast-in-situ layer, while the models represented Sample 7 failed with a horizontal crack along the interface, a flexural crack at the end of coupling reinforcement, and a crack at the stirrup location in precast layer. From the verification study, the reinforcement bond-slip function (CEB-FIB 2010) was chosen not to be used for the rest of the study since it did not affect much the load capacity and the failure mechanism of the specimens. Consequently, pull-out failure of the stirrup is excluded for the rest of this study. Prior to the main study, the influence of each interface parameter was studied in both unreinforced and reinforced interface models by varying the interface parameters. It was observed that interface tensile strength and stiffness are governing in the unreinforced interface model. Within the range of those parameters, the load capacity was increased and decreased by more than 50% in compared to the reference model verified by Sample 1. By adding a rectangular stirrup near the joint of unreinforced interface model, the model with reinforced interface has a different governing parameter, the cohesion, and the variability of the results decrease. Within the range of the cohesion, the load capacity was increased and decreased up to 30% in compared to the reference model verified by Sample 7. Since the interface parameters influence the capacity of both unreinforced and reinforced interface beams, two different interface types are used for the whole of the study. They are known as “smooth interface” which uses the parameters obtained from the verification with the experimental specimen, and “perfect bonded interface” which use rigid connection between the elements of the two concrete layers. To study the influence of lap splices spacing, models with three lap splices setup from Harrass’ experiment (three coupling reinforcements and three bottom reinforcements) were compared to models with a single lap splice (one coupling reinforcement and one bottom reinforcement) with the same total reinforcement area. As a result, with perfect bonded interface, model with single lap splice has higher load capacity by more than 10% in compared to model with three lap splices though both models failed with the same failure mechanism which was the horizontal crack along coupling reinforcement and a flexural crack at the end of coupling reinforcement reaches the top of the cast-in-situ layer. Stress concentration around coupling reinforcements were observed in all models, especially in model with single coupling reinforcement. However, different horizontal crack propagation occurred in each models. Uniform horizontal crack propagation along the interface were observed in models with smooth interface, while more concentrated crack propagation around the coupling reinforcements were observed in models with perfect bonded interface, especially in model with single lap splice. This different crack propagation in models with perfect bonded interface could be the cause of different load capacity since more uncracked elements could provide more tensile force transfer from precast layer to cast-in-situ layer. In the study of the influence of stirrups spacing, models with rectangular stirrup (two legs) setup were compared to models with a single leg vertical stirrup setup with the same total reinforcement area. In both cases the presence of the stirrup near the joint stopped the propagation of the horizontal crack. As a result, all models could reach yielding of the coupling reinforcement for both interface types although different structural stiffness is observed. The plausible cause for this difference in structural stiffness was the higher tensile stress in stirrups of model with two legs stirrups compared to model with single leg stirrup. This higher tensile stress might be resulted by the more distributed stirrups across the width of the beam. In the additional study, models with full height lateral restraint at the support were compared with models with simple support. As a result, with perfect bonded interface, model with lateral restraint has higher load and displacement capacity by more than 14 and 2.5 times consecutively compared to the model without lateral restraint. In compared to the collapse load, the numerical result of model with lateral restraint has higher load capacity by almost 4 times. With smooth interface, model with lateral restraint has higher load and displacement capacity by more than 10 and 5.5 times consecutively compared to the model without lateral restraint. In compared to the collapse load, the numerical result of model with lateral restraint has higher load capacity by more than 2 times. These increases are in accordance with a research by Ockleston [2] which found a considerable increase of load capacity on concrete slab with lateral restraint compared to the yield line theory. Part of the increase of capacity was resulted by the fix boundary action due to bending moment at support. However, it was observed that compressive membrane action started to develop after the first flexural crack as the horizontal force at support rapidly increased after that crack. Although the models with lateral restraint of both interface types had a different failure mechanism compared to the models without lateral restraint, they have a similar final stage of the failure mechanism, which is the flexural crack at the end of coupling reinforcement. This flexural crack propagation can be prevented from occurring earlier due to the high compressive stress at the top part of the cast-in-situ layer. When the concrete crushed at the support due to limited rotation capacity of the concrete, the compressive stress dropped causing the flexural crack at the end of coupling reinforcement to develop. In conclusion, there was an influence of the interface behaviour to the failure and the capacity of composite SHCC-concrete beam. However, the influence was varied, depending on the coupling reinforcement spacing, presence of stirrup crossing the interface near the joint, spacing of stirrup, and interface type. It is also concluded that compressive membrane action in addition to fix bending action, which occurred due to the lateral restraint, increased the capacity of the structure. This increase depended on the interface type and rotation capacity of the concrete. A wider range of the influencing parameters are needed in future studies to get a more robust results which are beneficial for a more general conclusions. However, the series of experimental research based on this study are essential to provide a verification on the results of this numerical study.

The hyperloop system is a new transportation mode, which consists a magnetic levitating capsule-like hyperloop pod and a vacuum tube. Due to small air hindrance, the hyperloop pod is conceived to have a maximum speed of 333 m/s. If such a hyperloop system is to be built underground in soft soils, the hyperloop speed can easily reach the wave propagation speeds in the soil. Strong wave radiation is expected when the hyperloop is travelling at wave propagation speeds, which are called the critical speeds. The first objective is to analyse the dynamic influence from the hyperloop. A linear elastic half-space with an infinitely long concrete tunnel buried at a certain depth has been modeled. The excitation of the system is a hyperloop modeled as a moving constant load acting at the tunnel invert. In this thesis, a so-called indirect boundary element method (BEM) is applied. Indirect boundary integrals are formed which rely on the fundamental solutions for the interior medium, the two-and-a-half dimensional Green's functions. These 2.5D Green's functions are essentially the steady state solutions of the half-space subjected to a spatially varying line load. The space is assumed to be infinitely long and invariant in the direction parallel to the axis of the tunnel. Before implementing the BEM model, two improvements have been made to the 2.5D Green's functions: a better convergence of the Green's function surface-related terms and a better satisfaction of stress-free boundary conditions at the free surface. The accuracy and correctness of the boundary element model using the improved Green's functions have been verified by intensive case studies. Firstly, the scattering of 3D harmonic seismic P waves by a cavity and a tunnel in a linear elastic half-space is analysed. Results are validated by comparing to those from literature. Secondly, the BEM model is employed for the moving load problem. The embedded concrete tunnel is modeled using the Donnell's theory for thin shells. A coupled form of the indirect boundary integrals is formulated. Using the same model parameters, the results obtained by the BEM are in good agreements with those from literature. Moreover, a parametric study has been conducted to study the effect of moving load velocity, tunnel depth and thickness of concrete lining on the dynamic response. As a second objective of the current thesis work, the BEM model is compared with a finite element method (FEM) based model, developed by Movares B.V. The models are compared in both accuracy and computational efficiency. In the FEM model, the moving load is considered as a series of consecutive short pulses. The contributions from all the pulses are synthesized using a convolution. Furthermore, since the space is invariant in the direction parallel to the tunnel axis, it is possible to apply just one stationary impulse load in the finite element model. Using this method, a constant moving load and a moving load with acceleration are modeled. The FEM results are found to have close agreements with those by the BEM. Besides the Rayleigh wave speed in the soil, a second critical velocity which is related to the wave propagation in the tunnel is found. Furthermore, the case where a hyperloop runs constantly at the Rayleigh wave speed is more crucial than the case where the hyperloop accelerates and passes the Rayleigh wave speed.

Existing reinforced concrete (RC) structures can be strengthened using Strain Hardening Cementitious Composites (SHCC). The ability of SHCC in exhibiting a ductile response under tensile load due to strain­-hardening after crack initiation makes it a viable material to be used in, both, construction and retrofitting of concrete structures. The main objective of this research is to study the shear behaviour of SHCC-strengthened RC beams using NLFEA. The shear behaviour of benchmark RC beams is analysed first. The analysis of the selected RC beams analysed using Damage-based shear retention function results in accurate predictions of peak load if a fine mesh size resulting in 30 or more elements in the height of the beam is used. However, the failure type is predicted inaccurately for both coarse and fine mesh sizes due to lack of consideration for aggregate interlock in Damage-based shear retention function. The analysis of the selected RC beams using Al-Mahaidi shear retention function results in accurate predictions of peak load if a coarse mesh size resulting in 20 elements in the height of the beam is used. The failure type is also predicted accurately using Al-Mahaidi shear retention function with the stated mesh size. The consideration for aggregate interlock implicitly in Al-Mahaidi shear retention function in the form of shear retention factor allows for accurate prediction of both peak load and failure type. After analysing the shear behaviour of RC beams, the shear behaviour of a reinforced SHCC beam is analysed using Al-Mahaidi shear retention function since it can predict both failure load and failure type accurately for RC beams. In comparison with experiment, the peak load for the reinforced SHCC beam is underestimated and the failure type is also incorrectly modelled. Use of embedded reinforcement results in excessive cracking along the reinforcement, causing convergence issues at a load lower than the experimental peak load. Such excessive cracking is not observed in RC beams since cracks more localized in concrete as compared to SHCC, which exhibits multi-cracking behaviour. Therefore, the shear behaviour of selected reinforced SHCC beam using Al-Mahaidi shear retention function is not accurately modelled. After the analysis of shear behaviour of concrete and SHCC separately, their behaviour is studied in the form of SHCC-RC hybrid beams. The solution strategy consisting of Al-Mahaidi shear retention function is used, and different types of hybrid interface are modelled. The results show that peak load and failure type are accurately predicted when a numerically perfect bond is modelled at hybrid interface for hybrid beams exhibiting no debonding during experimentation. This is in case of a mesh size resulting in 20 elements in the height of beam used. The peak load and failure type, however, are inaccurately predicted when delamination is modelled at the hybrid interface for hybrid beams failing due to delamination during experimentation, irrespective of the mesh size considered. This is due to the inability of the Coulomb friction interface model in recognising significant delamination at the hybrid interface as a reason for the failure of the hybrid beam.

It has been reported that due to the rapid urbanization and economic growth the municipal solid waste (MSW) would double in volume from 1.3 billion tons per year (in 2012) annually by the end of 2025, challenging environmental and public health management worldwide. Given that, most of the MSW incineration (MSWI) bottom ash (BA) are disposed in landfill currently, and technically and economically viable techniques for the reuse and recycling of MSWI BA is still at a premium. This issue would seriously challenge the environmental and public health management worldwide. In some European countries and the US, MSWI BA has been utilized as aggregate in pavement construction or as aggregate in concrete. Previous studies also proved the feasibility of using MSWI BA in concrete, either as aggregates or binder substitute materials. However, it is worth noticing that there are several significant drawbacks of using MSWI BA in concrete, including the potential risk of leaching due to the existence of heavy metals and harmful salts, the low reactivity due to high content of quartz and unburned organic matters, and the metallic aluminum-induced expansion. Therefore, in this study, a characterization of as-received MSWI BA was conducted at the beginning to find out the potential problems when used in concrete, namely the metallic aluminum content, low reactivity and unburned organics. A comprehensive pretreatment was performed subsequently to solve the problems. Specifically, both physical and chemical treatments were carried out to get rid of the metallic aluminum in BA. Afterwards, thermal treatment was conducted to enhance the reactivity of BA and remove the unburned organics. Pre-treated BA samples were characterized again to reveal the effectiveness of pretreatment. The results showed that both chemical and physical treatment were highly effective in removing metallic aluminum. Meanwhile, thermal treatment was proved to be a proper activation method which also removed the remaining organic matters through the high-temperature process. Subsequently, the investigations of the effects of pre-treated BA addition on compressive strength, reaction products and hydration heat development were conducted on cement paste level by varying the replacement material (BA with different treatment methods) and ratio. A proper method of pretreatment was proposed as well as an optimization of a maximum replacement level of BA in cement paste without detrimentally influence the performance of concrete paste was studied. Compared with nonreactive micronized sand (only works as filler) and pure cement, the addition of physically treated BA has a certain amount of contribution to the hydration process from the viewpoint of heat release. Results show that BA do have pozzolanic activity but is much lower than cement, and physically treated BA is suitable to be used as filler in concrete. Additionally, physically treated BA was further activated through thermal treatment according to the result of compressive strength test, which delivered the highest strength among all the treated BA under the same replacement ratio. Finally, to extend the application of MSWI BA in concrete, the mix design was made by blending treated BA with the highest compressive strength into concrete and make it suitable for structural application. The effects of treated BA addition on the workability and compressive strength of concrete were investigated. The addition of treated BA brought slight negative impact both in workability and strength due to the existence of nonreactive phases in BA (quartz and organics). Accordingly, this study proved the potential of BA with proper treatment to be used as a cement substitute material in concrete as well as promoted the understanding of the influence of BA on the hydration process, which also brings the possibility that BA could be widely reused in concrete system in future industry.