Highway traffic bridges have been subjected to increasing loads over the past decades. Some of the movable bridge leafs in these highway bridges were constructed in the 1960s and they are now close to the end of their intended life span. These bridge leafs were typically designed and executed with hardwood deck boards. In the initial design calculations, traffic loads were smaller, complex calculation by computer models did not yet exist. Therefore, some phenomena like for example fatigue and global hybrid interaction were never considered. Since some movable highway bridges are now due to be re-assessed, there is a growing need to gain knowledge on the way timber decks are functioning within the movable bridge leaf. These bridge decks have sustained all loads throughout the years without significant damage, but we don’t know whether these timber deck boards help the main load bearing steel structure as well. Or in other words; do the timber deck boards interact with the steel girders in the current situation? In this research, the degree of hybrid interaction was measured in terms of the magnitude of the main girder deflection for the reference case of the Bridge across the Beneden Merwede. The main girder deflection for bolted connections, having a certain free slip and embedding stiffness, was determined by running a linear sequential secant stiffness analysis. This analysis approximates a physically non-linear analysis. The maximum deflection of the main girder was compared to the maximum main girder deflections for no hybrid interaction versus full hybrid interaction. The resulting global deflections from the Secant Stiffness Analysis have shown that practically no hybrid interaction can be found between the current deck and the steel structure. For retrofitting options, the level of hybrid interaction can be significant. An increasing or decreasing degree of hybrid interaction did not only change the forces and moments in the steel girders, but also had a considerable effect on the deck and its connections. There is a gain and a loss for every retrofitting option considered. Decision-making for retrofitting timber bridge decks should take multiple contradicting criteria into account. An optimisation could be necessary in order to take a well-advised decision. ... Read more

In the design of steel structures, optimisation methods promise cheap, light and sustainable structures. However, the resulting designs tend to have a high diversity of profiles, making them unbuildable. Furthermore, the optimisation problem is mathematically complex, leading to a long and potentially unsolvable optimisation process. Grouping methods solve both issues by finding the optimum solution, for which the number of distinct profiles is limited. Multiple grouping methods exist in literature, and it is not known which is the best: the methods have not been applied on the same problems, and the computational effort has not been compared. This gap in literature leads to the following question: “Which method for grouping can find the lightest and cheapest steel structure with minimal computational effort?” To answer this question, a comparison of the existing grouping methods is made on their theoretical and numerical performance. The theoretical comparison comprises the size and properties of the search space, and the number of additional calculations. The numerical comparison consists of weight optimisation of eight benchmark problems. For each structure and method, the weight of the solution and corresponding computational effort is evaluated. Manually grouping of members, which is the most popular grouping method, relies on the engineer’s expertise and rules of thumb. This method requires no additional calculations but in general fails to find the optimum grouping for a light or cheap structure. Other existing methods include the geometry, axial force distribution or an ungrouped result in their grouping process, or adapt the optimisation problem. Of these methods, only the cardinality constraints method is guaranteed to potentially find the lightest grouped design, while reducing the search space for a small number of groups. However, it creates many local optima, which increases the complexity of the search space. In the aim of finding a grouping method which creates a simple and small search space and has low computational effort, the fully stressed combinatorial search method is proposed. In this method, the grouping is found by a combinatorial search, which evaluates the estimated weight or costs of a restricted set of groupings based on the weight per unit length of the members of a fully stressed design. Then, optimisation of a small and simple search space finds the corresponding optimum profiles. These steps are repeated, in which the fully stressed design uses the result of the previous optimisation as its reference design. The loop repeats until the grouping is unchanged, or the result diverges. In all numerical experiments, the new method gave results with a low weight, while it kept the computational effort to an acceptable level. It gave the lightest design for four out of eight problems and showed high certainty for converging to the lightest design in two problems. For the other two problems it performed second best. Conclusively, this method is the best available grouping method for steel structural optimisation. In case of cost optimisation, the new grouping method can efficiently find the optimum design including the optimum number of groups; the new method converges to cheaper design with less computations than in the case no grouping is applied. For a real-life case-study, the costs of a design were reduced with 7.3% compared to a manually grouped design and with 19.6% compared to the conventional design process. I suggest that further research focusses on further development of the new grouping method as proposed improvements can be made on the initial design, and the number of computations in the combinatorial search and fully stressed design. Moreover, the effectiveness of a suggested simplification of the new method should be investigated. This would allow application for engineers who are not able to apply a mathematical optimisation method. For practical application, incorporation of building codes and cost functions with a well-defined scope are desired. Finally, utilisation of the grouping methods in other applications is possible, but the performance of the methods should be evaluated per application. ... Read more

Structures may be subjected to both mechanical loads and imposed deformation. On one hand, the mechanical loads include, for example, the self-weight of the construction work, the action from normal use by person, furniture and movable objects, vehicles, snow, wind, execution, etc. On the other hand, when the deformation of a structure is restrained, imposed deformation occurs. The sources of deformation can be various, not only environmental conditions, such as temperature and humidity changes, but also chemical or physical actions, such as sulphate ingress or creep. If the shortening of a structure is restrained, the structure will be subjected to imposed deformation which results in tensile stress. Since the tensile strength of concrete is relatively low, concrete structures, such as tunnels, bridges and pavement roads, always suffer a high risk of cracking. Even if the concrete structure is prestressed, the tensile stress resulting from imposed deformation would consume the compressive stress in concrete and raise the risk of cracking. If the crack width exceeds the limit, leakage, corrosion and even structural failure may happen. According to the schematized 푁 - 휀 diagram of reinforced concrete, the development of cracking caused by imposed deformation and mechanical load are different. Suppose the cracking is caused by imposed deformation, there is a developing stage for cracking. It means the cracks caused by imposed deformation could be either fully or not fully developed. However, suppose the cracking is caused by mechanical loads, the cracks could only be fully developed. The stiffness of fully or not fully cracked members are different. The stress resulting from imposed deformation in a structure is related to the stiffness of the structure. Therefore, cracking has significant impact on the magnitude of stress resulting from imposed deformation. Therefore, when a structure is subjected to imposed deformation and mechanical load together, it is necessary to take the impact of cracking into account during structure design. The combination of imposed deformation and mechanic loads is referred to as combined actions. It is common to use FEM software to analyze the stress resulting from the combined actions during structure design when cracking has to be taken into account. However, FEM analysis only is not enough. It is also necessary to check the results calculated by FEM software to avoid mistakes, for example a wrong input.
There is a project called 'Approach Ring South, Groningen'. In the project, widened deck KW03.01 is subjected to a combination of imposed deformation and prestressing force. FEM software called SCIA is used to calculate the prestress consumption in the widened deck KW03.01. According to the data file of the project, 41% in maximum of the compressive stress resulting from prestressing is consumed when the structure is subjected to combined actions, which is much more than the engineering experience. As a result, a simple approach is required to check whether the prestress consumption in widened deck KW03.01 suits the expectation or not, where the prestress consumption is calculated by FEM software. ... Read more

Gas-induced earthquakes are a major problem in the north of the Netherlands due to many unreinforced masonry (URM) buildings being located in this area. To improve the seismic performance of the URM buildings, existing structures must be retrofitted and if the aesthetic of the building is important, the implemented retrofitting technique must not alter the appearance of the property. An experimental campaign was conducted at Delft University of Technology to investigate whether bed joint reinforcement (BJR) can be used for seismic retrofitting of URM walls. In this thesis, the influence of BJR, diagonal anchors and reinforcement layout on the in-plane seismic behavior of the retrofitted wall is studied. To achieve this goal several nonlinear static analyses using DIANA software were performed. First, the case experimentally tested is adopted as a benchmark and a validation of the numerical model is performed. Afterwards, the validated numerical model is adopted to perform a parametric study considering different reinforcement layouts. The numerical study showed that BJR was able to improve the seismic performance of the retrofitted wall. The Peak-load was increased slightly (13%) in the retrofitted wall compared with the URM wall. BJR acts in tension to restrains the crack opening so, the maximum crack width is another affected factor: a difference of -110% in maximum crack width was observed after retrofitting. Finally, the crack pattern and failure mechanism of the structure was changed due to BJR. The sensitivity analysis showed that the results were sensitive to variation in tensile fracture energy and modulus of elasticity, while tensile strength, compressive strength, and compressive fracture energy were the other variations that did not affect the results considerably. According to an extensive parametric study, it was concluded that double BJR was slightly more effective than single BJR. By applying only 4 layers of double BJR almost the same peak-load and maximum crack width were obtained comparing the results of the retrofitted wall with the original layout (with 12 BJR layers). The location of the BJR, however, was the governing concern. In the URM wall cracks mostly developed diagonally from the window corners and by applying horizontal bars below and above the window opening, the diagonal cracks were restricted and failure modes of the wall changed. The absence of single BJR next to the opening (in piers) might lead to the shear mechanism of the piers. The number of BJR is a function of the opening’s dimension. According to a proposed reinforcement layout it is believed that the mentioned 4 layers of double BJR (above and below the opening) and 3 layers of single BJR (next to the opening) were a wise choice for retrofitting of the wall. Furthermore, diagonal anchors could be ignored as they did not affect the performance of the wall. Conservatively, a layer of double BJR far above and below the window level could be applied. In this way reinforcement was decreased by 30%, however, the results were comparable with the retrofitted wall with original reinforcement layout. ... Read more

This thesis aims to come up with a preliminary design for the in- and outlet structure, in which pump-turbines are housed, of the energy storage lake within the Delta21 plan. The goal is to come up with a feasible, cost-effective and lasting solution, that can store green energy, pump out 10 000 m³/s of water and retain design storms, the classic design steps are followed. The method followed, starts with an analysis of the problem, giving insight to the relevant stakeholders and functions that should be included. These elements lead to the Program of Requirements, which contains research into the tailor-made pump-turbine system and present-day water levels. The analysis ends in presenting the boundary conditions. This thesis continues with several concepts that fulfil the functions and requirements. For those concepts, the possible construction methods are described, and checks are performed to verify the stability, including 1) piping, 2) rotational stability, 3) sliding, 4) bearing capacity and 5) (static) floating stability. Using the evaluation criteria from the analysis, described after the Program of Requirements, and weighting factors, following from the stakeholder analysis, the value of the different alternatives is calculated via a Multiple-Criteria Decision Analysis and compared to each other, by including costs. Lastly, one more iteration is made to check the strength of the walls and floors of the most desirable alternative. It can be concluded that the most straightforward alternative, called `Unity', is more cost-effective than an alternative integrated into the dune surrounding the energy storage lake. Also, the minimum width of that caisson, which is 53 m and follows from the pump-turbine system, can be achieved according to the stability checks. The author recommends checking the interaction between the spillway and the in- and outlet structure and model the foundation of the caisson more thoroughly. ... Read more

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

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. ... Read more

A combination of conventional concrete members with innovative material such as Strain Hardening Cementitious Composite (SHCC) in the tensile zone, can exhibit better crack-width control. This is attributed to the bridging effect by the Polyvinyl Alcohol (PVA) fibers used in SHCC in combination with the special material composition containing fine particles. This hybrid combination is able to satisfy the Serviceability Limit State (SLS) criteria for crack-width control by eliminating the requirement of additional reinforcement. Optimisation of micro-cracking of SHCC requires an investigation to study the influence of the interface in SHCC-Concrete hybrid beam and the type of fiber used in SHCC. This master thesis research is a continuation of the previous Msc. thesis study performed by Zhekang Huang [1] on the experimental flexural behaviour of reinforced concrete beams with a layer of SHCC in the tension zone. Variation in the bond interface property such as smooth interface profile, partially debonded, completely debonded and grooved interface profile are investigated to study their influence on the bearing capacity and crack-width control. To assess the impact of the type of fibers on crack-width control, commonly used PVA fibers are replaced with High Modulus Polyethylene Fibers (HMPE) based on pre-study. All hybrid beams are tested experimentally in a four-point bending set-up to generate cracks within the constant moment region and Digital Image Correlation (DIC) is performed to evaluate the crack patterns and the crack-widths. Numerical analyses of the beams are performed using Finite Element Analysis software Diana {version 10.3} with the modelling of similar interfaces and material properties used in the experiments. From the obtained results, it is observed that for all the beam specimens tested, varying the interface property did not have a significant impact on their bearing capacity as the interface within the constant moment region is only varied and the surface outside this region is bonded. For beam specimens with partial and completely debonded interface in the constant moment region, it is observed that the initial stiffness is reduced but the overall bearing capacity remains the same. Within the constant moment region, varying the interface property resulted in different crack patterns. The profiled and smooth interfaces, despite exhibiting different crack patterns, reached the maximum allowable crack-width of 0.3 mm at similar load steps of 69 KN and 71 KN respectively. This is because a sufficient bond at the interface is developed and as a result, due to local adhesion, the surface roughness plays a minor role. The beam specimens with completely and partially debonded interfaces localised at a much earlier load step of 45 KN and 50 KN respectively. This is because the stress generated in the SHCC layer is higher due to the severely cracked concrete layer on top. The beam specimens with smooth interface and HMPE fibers in SHCC perform similar to the beams with smooth interface and PVA fibers in SHCC. This is because of the additional constraint created due to the conventional concrete layer at the top in the SHCC-concrete hybrid beam. Despite the higher flexural capacity of the SHCC layer containing HMPE fibers, the concrete layer crushes much before the SHCC layer fails, thus, compromising the performance of the hybrid beam. By reducing the interface stiffness properties, an effort is made to reproduce the behaviour of specimen beams in four-point bending test through numerical modelling on Diana FEA. However, the prediction of the number of cracks formed and the crack-widths is inaccurate for all the beam specimens modelled. This is because the material models and interface properties available on Diana FEA to the authors knowledge, are insufficient in replicating the experimental cracking behaviour. ... Read more

Study of interface behavior has been the primary area of focus for researchers in the field of concrete science and technology. This interface between two concrete elements becomes important for prefabricated systems, combination of precast and in-situ concrete elements, combinations of concrete cast at different times, repairs of existing concrete structures, strengthening of a structural element such as beam or slab and so on. In this research an attempt is made to check if the interface behavior is reliably predicted using finite element analysis in ATENA with the help of standard elements available in the software. Validation of the numerical results is performed by simulating an experimental bond test and structural test and conclusions are drawn based on the response of these numerical models.

Strength of the interface is mainly governed by the roughness of the adjacent surfaces. In the literature study, a chronological overview of the development of shear models is presented that make use of these roughness parameters in calculating shear capacity of the interface. A finite element analysis is performed using standard elements available in ATENA. ATENA interface material model (ATENA IMM), present in the software uses 2D line interface elements having zero thickness to model an interface. Roughness parameters assigned to this model are based on the guidelines proposed in different design codes. Many parameters need to be defined in this interface that are difficult to measure accurately from experiments. For this, a 5 mm thick artificial interface layer is created by using 2D linear quadrilateral material elements. This technique is named as artificial interface model (ArtIM) that uses physical material properties to define the interface. Since, cohesion and friction coefficient parameters cannot be specifically defined in ArtIM unlike in ATENA IMM, an explicit roughness is incorporated by designing the interface layer in a wave pattern with certain wavelength and amplitude depending on the different surface roughness classes as defined in the Model Code 2010.

A check is performed for the assigned input parameters for the two interface modelling techniques, by simulating bond tests (direct tension test and shear load test) on a small scale composite concrete specimen. Furthermore, validation of the two interface modelling techniques is carried out by comparing the numerical results to experimental findings for a bond test performed by T. Paulay, R. Park and M. H. Phillips [1] and for a structural test case of the Eindhoven airport car park garage failure [2], [3]. ATENA IMM rightly predicts the initial response of the interface but does not comply with the experimental results once the interface fails. With the use of ArtIM, an overestimation of the shear strength is exhibited and the conventional ratio of 2 between the shear and tensile strength [4], [5] cannot be obtained. Moreover, once the material in the interface layer fails, a brittle behavior is exhibited pertaining to the concrete properties assigned to the interface material layer.

Different reinforcement modelling techniques are studied using ATENA IMM with a very low bond strength (no bond condition). The default 1-D reinforcement (RF) bar element when modelled perpendicular to the interface does not reliably predict the response of loading. Hence, other RF modelling techniques are discussed among which, 1-D RF bar elements modelled in cross pattern reliably predict the initial stiffness of the RF bars. The inclination of the RF bars was tested for different angles to comply with the experimental results. However, further research is required to calculate appropriate inclination of the RF bars. In this case the optimum angle between the cross RF bars and interface is around 80°.

In the structural test, interface behavior is investigated for a specimen with (fully reinforced) and without (partially reinforced) shear reinforcement in the flexural span. ATENA IMM safely predicts the bond strength in case of both, partially reinforced and fully reinforced models. However, by using ArtIM, an overestimation of the interface strength is observed. The important aspect in the structural model is the shear strength of the interface and since, while using an artificial material element for the interface the shear strength obtained is almost 40% higher than the experimental results, the ultimate load carrying capacity of the whole model increases manifold.

After investigating the two interface modelling techniques, on bond level and structural level, it can be concluded that, the ATENA interface material model (IMM) as well as the artificial interface model (ArtIM) do not predict the interface behavior reliably. However, by using ATENA IMM a conservative response is obtained as opposed to the ArtIM which overestimates the shear capacity of the interface. ... Read more

The Strut-and-Tie model (STM) is an efficient technique for the design of concrete structures, but the creation of suitable truss structures gets complicated when these structures become more complex. The topology optimization (TO) is a convenient technique that has been used in recent years for the creation of trusses of complex structures for the STM. This thesis presents a process for the creation of suitable truss structures for the STM using the results obtained with the TO, as well as, an evaluation of them to see which is the most optimal truss structure according to the total amount of tension force present on the full truss, this total amount of tension force is the selected evaluation criterion. Three deep concrete beams were analyzed using two topology optimization (SIMP and BESO approaches) for the generation of stress paths, these approaches are based on the minimization of the strain energy. The procedure starts with the computation of the principal stresses over the results of the topology optimization, then bar elements are placed over the stress paths of these diagrams creating a first (harsh) layout of the trusses. These trusses were not always found stable, but all the trusses were stabilized because, in this way, it is easy to calculate the axial force of in the truss elements, thus satisfy a basic requirement of the STM. To stabilize the truss structures two methods were explored. (i) The addition of new members outside of the stress paths (stabilizers), the essential characteristic of these new elements is that the axial force in them should be zero to not change the stress distribution found during the optimization process. A sensitivity analysis of the stabilizers was performed to track how the axial force changes in these members depending on the position of the nodes connected to them, this process was necessary because when an element outside the stress paths has axial force the stress diagrams have been changed. (ii) The creation of substructures within the stress paths, this process stabilizes the global structure without the addition of members outside the stress paths. Finally, a structural analysis was performed to obtain the axial forces in each member of the truss structure, and through an analysis of these results, the total amount of tension forces in the truss was computed. The truss with the minimum value of total tension force is assumed as the most optimal structure for each case. It is clear through the analysis that the variation of the input parameters does not cause large variations in the results of the topology optimization, but it has an impact in the stabilization process and the performance of the structures according to the evaluation criterion. Furthermore, it has been proved that suitable trusses for the STM can be created using any of the two selected optimization approaches obtaining good results, and a similar performance according to the evaluation criterion. ... Read more

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

In August of 2013 Elon Musk published his paper ’Hyperloop Alpha’, in which he describes an alternative transportation system for the to be built railway connection between Los Angeles and San Francisco. The Hyperloop system that Musk describes relies on partial vacuum tubes through which vehicles can travel at speeds up to 1000 km/h with great efficiency. An innovative breakthrough in the transportation sector if it can be made into a reality. Therefore his company SpaceX organised a contest to which many teams applied to built a concept vehicle to be used in the tubes. In 2017 a team of students from TU Delft won the overall prize for the best design and afterwards the team leaders founded Hardt to develop their ideas and make Hyperloop into a reality. BAM Infraconsult supports Hardt and together they develop the Hyperloop and its tube infrastructure. Currently the preliminary design for the tubes is made in steel and no alternatives have been considered. This research focusses on an alternative tube design in concrete. The tube has to not only satisfy the strict requirements that apply to the Hyperloop technology in general, but it also has to adhere to the specific design philosophy of the Hardt vehicle concept. A concept in which the vehicle is suspended from tracks on the ceiling of the tube by a series of magnets. The report is based on the following research question: Is a concrete design a feasible alternative for the design of airtight Hyperloop tubes compared to the considered steel tubes? To answer this question two philosophies are considered and researched into depth. Firstly a design in prefabricated normal strength concrete is analysed, making use of prestressing and conventional reinforcement, following the requirements set in the Eurocode. Secondly an innovative ultra high performance steel fibre reinforced concrete (UHPFRC) design is considered. Again prestressing is applied, however conventional reinforcement is not present in this design as it relies on steel fibres and prestressing alone. This design is modelled according to the French UHPFRC guidelines. A requirement for the design is that the inner diameter of the tubes is equal to 3.6 m and that the tubes span 30 m between pylons. The design methodology is based on a variable thickness of the tubes in order to find the optimal concrete structure that satisfies all requirements. Checks are made for multiple failure modes after which the governing minimum thickness is derived. Other than proving to be structurally sound according to the Eurocode, the tube also has to abide to a strict deflection limitation under dynamic loading conditions. In order to research this criterion the tube design is validated using finite element modelling. Here a combination of different parameters related to the concrete material characteristics and the dimensions of the tube is researched by means of a sensitivity analysis. Using the dynamic amplification factor specified by Hardt, the maximum deflections of the tube are checked and the parameters that have the greatest influence on the deflection are discussed. The obtained results are compared to the steel tube. Furthermore the possibilities for the construction of a concrete tube are considered, including a recommendation for the connections between tube sections. Moreover the transportation of the tubes to the building site and final assembly are taken into account. After all factors are considered a cost estimation is made for the design of the concrete tubes and compared to the cost estimation of the initial steel design of the tubes. This cost estimation does not only consider the material and production costs of the tubes, but also takes into account transportation, assembly, maintenance and site costs plus an allowance for risks and profit. It is concluded that a design in normal strength concrete is possible, but not practical. Its dimensions make the production and assembly very difficult. However a design in UHPFRC is feasible, as its required dimensions are considerably better. Furthermore it satisfies all structural requirements without the use of conventional reinforcement and even the strict deflection criterion at dynamic loading conditions can be achieved. Moreover the design in UHPFRC is a competitive alternative to the steel design, as it has a higher score when all criteria are considered. ... Read more

Orthotropic Steel Decks (OSDs) are widely used in various types of steel bridges due to their benefits of light weight, high load bearing capacity and speedy construction. Although many improvements in aspects of design, fabrication, inspection, and maintenance have been achieved over the years for such bridge decks, fatigue remains a predominant problem, mostly because of the complexity of prediction methods. Many researchers have tried to investigate this component through experiments. However, performing only experiments may not lead to a cost-effective solution. Therefore, it is necessary to combine the experimental data with the numerical approaches. Particularly Linear Elastic Fracture Mechanics (LEFM) allows to model and analyse the crack propagation until subsequent failure, and significantly reduces the requirement of experiment. ABAQUS® provides an enriched feature, commonly referred to as the Extended Finite Element Method (XFEM) which incorporates two enrichment function namely the discontinuity function which represents the gap between the crack surface and asymptotic function which captures the singularity and thus can be used to model discontinuity independent to the finite element mesh. To evaluate the modelling efficiency and validate the simulation methodology, two XFEM-model based on LEFM and Virtual Crack Closure Technique (VCCT) are developed and the simulated results are compared with the experimental data. The first phase of the thesis deals with the numerical simulation to investigate the crack propagation rate in Compact-Tension (CT) specimen for different stress ratios. The results of two-dimensional (2D) model are found to be in good agreement (within 1.48%) with the fatigue coupon test results. As most of the work concentrates on 2D shell model, the extension to three-dimensional (3D) solid requires the investigation of related parameters to consider through-thickness effects. Nevertheless, the mechanism of 3D model is studied, and the simulated results match with the 2D results for fatigue crack growth (a, N). Moreover, a reliable technique of computing Stress Intensity Factor (SIF) is obtained by comparing with the ISO 12108 standard formulation. However, when the SIF and fatigue crack growth are combined, the crack propagation rate in 3D is overestimated (about 26%) when compared to the experimental data possibly because of the imperfection in the application of boundary conditions. The second phase deals with the numerical simulation in welded connection of OSD to determine the Paris law constants (C, m) by correlating the numerical result of fatigue crack growth with the beach mark measurements obtained in the fatigue experiments. Prior to automated XFEM simulation, a set of finite element analyses are performed to determine the vertical deformation, longitudinal stain distribution and hotspot stresses to validate the numerical model as per the test setup. The results of numerical analyses showed a good correlation (within 18%) with test data and Paris law constant C is predicted to be lower than the recommended value by IIW standard. The validated methodology is then applied on large scale to an existing bridge (Suurhoff bridge) structure which was built in 1971. In this case study, a crack length of 230 mm was detected in the deck plate originating from the root of the stiffener-to-deck plate welded connection between the cross-beams using TOFD measurements. To verify the problem, a numerical model is developed based on the dimension of the bridge to evaluate the crack initiation period and the crack propagation period. The crack initiation period is predicted using hotspot stress method and the crack propagation period is evaluated using automated XFEM simulation. Overall, the total fatigue load cycles are predicted to be 7.86 million which is equivalent to 48 years. A similar crack length was however detected after a service life of 44 years. This overestimation can be possibly explained as the model did not take residual stresses and other welding defects into account. The numerical model showed a good correlation with the real scenario and is therefore used to predict the permissible limit of deck plate crack length of 500 mm. The model predicted 8.02 million load cycles for a crack length of 500mm, which is equivalent to 34 years after the crack initiation period. Nevertheless, the fracture mechanics approach showed improvements in the assessment of fatigue life. ... Read more

Crossing waterways is crucial to improve transport connections.
In particular, new crossing methods are needed when the distance to be covered increases. Submerged Floating Tunnels (SFT) have been recently emerging as a cost-effective feasible crossing technique to connect fjords in Norway. However, only very little research has addressed the vehicle-structure interaction, with attention to the passengers, so far. In the current thesis, an algorithm was developed to study the Fluid-Structure-Vehicle-Interaction (FSVI), where the tunnel has been modelled as a Euler Bernoulli beam, the train car as a 6DOFs system, the supporting cables as linear springs, and the fluid by the Morison's hydrodynamic force expression. The Sperling ride quality and comfort indices were used to address human comfort while crossing the tunnel. It is found that, due to the low-frequency hydrodynamic environment, the influence of the FSVI on the Sperling's indices is limited, i.e. "just noticeable" from the classification table. Low-frequency flow field may cause motion sickness rather than cause comfort/discomfort during the ride. The illness rating, which is the indicator of the motion sickness, gave positive outcomes due to the small amplitude of the accelerations, and therefore no illness is expected to be felt by passengers. This study shows that displacement and acceleration can be controlled and kept inside the proposed boundaries under storm sea states, and the comfort while crossing can be guaranteed. The approach here used can be applied to other sea states with higher frequency content to address the comfort in a storm with smaller return period, which may also be important to address the fatigue resistance of the structure. ... Read more

Throughout the years, incremental iterative approaches have been shown to be excellent tools in describing the complex behaviour of structures under a wide range of circumstances. However, robustness issues arise for quasi-brittle structures due to the potential lost of convergence during the development of abrupt fracture mechanisms. In order to overcome these robustness issues, the framework of sequentially linear analysis (SLA) has been proposed: an event-by-event strategy in which a sequence of scaled linear analyses with decreasing secant stiffness is performed, representing local damage increments. The current SLA-framework is based on a fixed crack approach, potentially causing the development of severe spurious stresses and inaccuracies due to the misalignment of the crack with the principal stress directions. To this end, Hendriks and Rots proposed a model consisting of several parallel fractions or layers, from now on called the sublayer model. Each of the layers is elastic-perfectly brittle, but has different properties, chosen such to represent the overall constitutive softening behaviour as accurate as possible. The layers fail independent of each other and have their own specific crack direction. The main idea is to mimick a rotating crack by a superposition of sublayers with a fixed crack direction. The main goal of this thesis is to further elaborate, generalize and verify the sublayer model for quasi-brittle materials and capture the influence of rotating cracks on the structural response within the framework of existing regular sequentially linear analysis. In this thesis, the frameworks of regular SLA and the sublayer model were connected by a general transition from any saw-tooth law to sublayer material properties. An externalized procedure was created to automatically generate an input file for DIANA FEA and thereby facilitate verification of the sublayer model. Furthermore, the 2-dimensional framework of the sublayer model has been extended towards 3-dimensional structures to broaden the range of application. On top of that, concepts were proposed to improve the sublayer model: the tapered ripple band, reducing the required number of sublayers to reach a specific state by adding more saw-teeth near the end of the softening curve, and an improved algorithm, making use of the fact that the order of brittle fracture of the sublayers is known in advance, such that only those integration points that can actually become critical are monitored, thereby reducing computational efforts significantly. In this thesis, the sublayer model is proved to mimick a rotating crack within the framework of existing regular sequentially linear analysis based on a set of structural case studies (notched beam, shear notched beam, DEN-beam, full scale facade and full scale concrete dam). Compared to regular SLA, effects of stress locking are reduced, less wide localization bands are found and a more realistic collapse pattern is observed, thereby making the sublayer model more interesting for application in engineering practice. Furthermore, it has been shown that for the 3-dimensional framework of the sublayer model the same conclusions as for 2D can be made. In the authors opinion, the contributions of this thesis are a step towards a robust generally applicable computational method to simulate the complex structural behaviour of quasibrittle materials. ... Read more

The Netherlands is a densely populated country with a congested road and railway network. Therefore more and more highways are widened and expanded. These wider highways create a demand for bridges which are suited for longer spans. These bridge solutions should constructed with a minimum of hindrance for other traffic. Rijkswaterstaat, also wishes to reduce the number of intermediate supports so the space underneath a viaduct can be used more freely. The currently most used solution to build a highway overpass without disrupting the traffic too much is a concrete viaduct consisting of prefabricated prestressed concrete bridge beams. But for spans longer than 60 meters those beams become too long and too heavy for transport by truck to the building site. Therefore the existing bridge solutions are reaching the maximum distance to which they can be built. The primary goal of this report is to find a concrete bridge solution with which it is possible to construct longer bridge spans in prefabricated concrete up to 100 meters. With such a bridge solution it is also possible to span a waterway or a small river in the Netherlands. A beam bridge in which the beam is composed of three parts is the most suitable solution to build these longer spans in prefabricated concrete. This solution can be constructed with relatively little hindrance for the other traffic. This solution is also relatively flexible in the shapes of bridge decks that can be constructed, skew bridges and wide bridge decks are both possible. The design of this beam bridge is extended and analyzed with a more detailed calculation. A bridge span of 100 meters is possible with a construction height of only 3 meters. This relatively slender design is possible because high strength concrete is used and because the bridge deck is designed to spread the traffic load efficiently over the full width of the bridge deck. The beam parts of this bridge can be transported by truck to its destination.
A rough cost estimation shows that the designed solution is expensive compared to existing concrete beam bridges, but it is also possible that the designed solution has a lower cost price compared to existing solutions in steel. It is advised to continue the research to and development of the bridge design because of the possible lower cost price and because with this design, bridges can be constructed which currently cannot easily be constructed with the existing solutions. ... Read more

Old bridges in the Netherlands are reassessed to prove their structural safety because of the increased traffic loads. The Eurocode model for the shear capacity of prestressed concrete beams with sufficient shear reinforcement was found to be very conservative for small amounts of transverse reinforcement, which is typical for old bridges. Code provisions based on the modified compression field theory appear to be much more accurate (Bentz, Vecchio, & Collins,2006). On the other hand, these models make no distinction between flexural shear and shear tension failure, while 25% of the bridges consists of T-, I-, or box beams which are sensitive to shear tension failure. The aim of this thesis is to present a more accurate prediction for shear tension failure based on the modified compression field theory (MCFT). The report focuses on both the CSA-model and Response-2000. The CSA-model is a simplification of the MCFT for beams under the assumption that σ_z=0. The CSA-model shear resistance consists of a concrete and steel part. Response-2000 is a cross-sectional analysis program that works as a non-linear finite element analysis and not only takes into account bending but also shear.Response analysis of 32 beams (experiments of Xie (Xie, 2009), Choulli (Choulli, 2005), Hanson (Hanson & Hulbos, 1965) and Leonhardt (Leonhardt, Koch, & Rostasy, 1973)) have been made and compared with the experimental observations. The failure load is predicted with a mean ratio of 1.38 and a COV of 19% compared to the experiments. It was found that for small a/d-ratios predictions are more conservative. Failure mechanisms: rupture of the stirrups, crushing of the web concrete and slipping/major crack opening are found in Response. 87% of the failure mechanisms was predicted correctly compared to the experiments. The critical cross-section compared with the experimentally observed failure zone showed that 60% of the beams was predicted in the failure zone. The shear force in the cross section is resisted by reinforcement steel, aggregate interlock and the uncracked concrete, which were found to take up respectively 1/2, 1/6 and 1/3 of the shear force. The steel part is predicted accurately while the aggregate interlock part is underpredicted due to an over prediction of the crack spacing. The uncracked part is overpredicted for small amounts of reinforcement and underpredicted for larger amounts of reinforcement. The data of the Response analysis have been used to modify the CSA-model to a model solely describing shear tension failure. The comparison showed that the CSA-model underestimates the steel part, overestimates the concrete part, takes a to large cracked height and doesn't take into account the contribution of the uncracked part. From this comparison, modifications for β,θ,V_max,h_crack and ϵ_x are proposed using Response data and proposals from Esfandiari (Esfandiari & Adebar, 2009). The flanges are taken as uncracked and the contribution of the uncracked part is described with a linear elastic shear stress distribution. This has led to a proposal for a model that solely describes shear tension failure, where the most important addition is the contribution of the uncracked height. Calculations show that the model gives conservative predictions compared to the experiments (mean ratio of 1.36 and a COV 22%) and the predictions are almost the same as for Response. The parameters are predicted conservative compared to the Response-2000 predictions. ... Read more

Skid resistance is an important parameter for road safety and therefore it is essential to monitor the skid resistance of pavements. In the Netherlands, skid resistance is measured with either the RWS Skid Resistance Tester -measuring the longitudinal friction coefficient- or the Seitenkraft-Messverfahren (SKM) -measuring the sideway friction coefficient. The latter is nowadays the preferred measurement device by Rijkswaterstaat. Skid resistance depends much on the vehicle speed: the higher the speed, the lower the skid resistance. Furthermore, the texture of the surface influences the speed dependency. Because it is not always possible to measure the skid resistance at target speeds set by Rijkswaterstaat, there is a demand for a speed conversion model for the skid resistance measured with the SKM. The objective of this research is therefore formulated as follows: the development of a speed conversion model for the wet skid resistance, measured with the SKM at different speeds, taking into account the macrotexture of the road surface. The used dataset consists of 718 sections of 100 metre, measured at the Dutch road network. Measurements were performed at 10 different roads with different pavement layers: porous asphalt, concrete pavements, dense pavements and stone mastic asphalt. The mean profile depth of the pavements varies between 0.21 and 1.80 mm. The performed measuring speeds were 40, 60 and 80 km/h, and for few sections 30 km/h. Three regression methods were performed. Firstly, a multiple linear regression was performed. The datapoints consisted of combinations of two measurements at different speeds on identical 100 metre sections. The second method estimated per 100 metre section a zero speed intercept which was used as a reference point. The third method used multilevel modelling and includes a hierarchical structure. Concluded was that the multiple linear regression on speed combinations is inappropriate for the objective of this research, because of two reasons: the datapoints are dependent on each other, and information is lost by splitting the 100 metre sections into datapoints with combinations of two measurements. In the second method, problems arise with estimating the zero speed intercept. The third method is most appropriate for this research and the three-level structure fits best on the dataset. The first level contains the individual measurements on the 100 metre sections, performed at different measuring speeds. The second level consists of the 100 metre sections and the third level consist of the roads on which the measurements took place. The standard error of the model on the training data is 0.032 whereas the average change in skid resistance for two datapoints is 0.053. This average change includes conversions over a speed difference from 10 to 40 km/h. From a sensitivity analysis of the macrotexture it was concluded that if no macrotexture can be measured, it is advised to use a different model in which no macrotexture is included. Recommendations for further research include among others registering more accurately the type and age of the measured pavements and extending the dataset with measurements performed at low measuring speeds and on curved sections. Furthermore, it is recommended to perform a more comprehensive outlier analysis and to optimise the hierarchical structure. ... Read more

Ageing of bitumen has been long-recognized as one of the major reasons responsible for the gradual deterioration of asphalt pavements. Age-hardening of the binder leads to the embrittlement of the overall asphalt mixture, which entails its increased susceptibility to traffic and environmental induced damage. As a result, high maintenance efforts as well as increased expenses are required to allow for an asphalt pavement to reach its expected service-life.
Past research efforts have established a solid background with respect to the implications of bitumen ageing on the overall response of an asphalt mixture as well as on the binder’s physico-chemical properties. In the same framework, studies have demonstrated that the ageing process of bitumen in the field is not solely a function of the bitumen type itself, but rather, added effects have been identified attributed to the mineral matter and the asphalt mixture design parameters.
This thesis attempts to provide a deeper understanding of the effect of mineral aggregates on the ageing of bitumen, and more specifically, the effect of a special fraction of the solid phase in asphalt mixtures, the mineral fillers. Six different mineral fillers were employed in this research, covering a wide range of physical and composition-related (i.e. elemental/mineralogical) properties. Bitumen-mineral filler blends were prepared, according to a single design protocol, and the resulting mastics along with neat bitumen were subjected to accelerated laboratory ageing by means of the Pressure Ageing Vessel.
The rheological (i.e. Dynamic Shear Rheometer) evaluation of the resulting materials and the derivation of ageing indices revealed the overall ability of the mineral fillers, regardless of their individual properties, to mitigate the ageing of bitumen incorporated in the mastics. The chemical (i.e. Fourier Transform-Infrared Spectroscopy) investigation of the materials showed that, in fact, the chemically active mineral fillers catalysed the oxidation of bitumen incorporated in the mastics. These results allowed for the identification of two mechanisms through which the effect of the mineral fillers on the ageing of bitumen occurs. The first one is related to the physical presence of the mineral matter in the mastics, whereas the second one to the developed physico-chemical interactions between the mineral fillers’ particles and the bitumen. Basic mineral fillers were found to be more efficient in reducing the age-hardening of mastics, compared to acidic ones, by allowing for more intensive interactions between the mastics’ constituent materials. Moreover, there are indications that the mineral fillers’ specific surface area also has a primary role to the developed interactions, and, by extension, to the ageing behavior of the mastics.
Finally, in addition to the aforementioned main findings, binders were extracted and recovered from the aged mastics, in an effort to derive further information on the effect of mineral fillers on ageing of bituminous mixtures by investigating the aged mastics’ constituent materials on their individual level. The rheological and chemical examination of the recovered materials did not lead to any further insight regarding the research questions of this study. Instead, features were revealed which manifest that the extraction and recovery of bitumen may not be a suitable approach for the investigation of the research problem addressed in this thesis.
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This research studies a simplified connection between one storey high concrete columns and the continuous floors with an integrated steel beam, of the THQ type, carrying hollow core slabs and covered by a reinforced structural screed. The final goal is to determine the strength of the connection. This is done with a calculation method, which may be used outside of this research by designers for an estimation of the design strength of their connection. A simplified design for the connection is set up as a reference design. It is loaded by two load combinations of the use stage of the building, a symmetric and an asymmetric load combination. A behaviour prediction is set up for the reference design under these load combinations. Based on that prediction, additions to the design are studied, which should improve the connection strength. Two adjusted designs are chosen to analyse alongside the reference design: a design with the integrated steel beam supported by additional steel webs at the connection and a design with the integrated steel beam being filled with mortar at the connection. The three designs are numerically modelled and analysed with the Finite Element Analysis (FEA) in DIANA FEA. With the results of the numerical analysis, the design strength of the connection is calculated. The numerical results show that the structural screed and the bottom column are the governing connection parts. The structural screed in the reference model is influenced most by the steel webs of the beam underneath and a limited load transfer area, which leads to higher stresses in the concrete. In the adjusted models this situation is improved, with the model with a mortar filling being the best adjustment, as it provides the maximum load transfer area. The bottom column is most affected by the bending of the steel beam flanges due to the load of the floor, causing a large load to be transferred over a small area at the column edges. The adjusted models do not show a strong improvement here, as the adjustments are limited in the stiffening of the beam flanges. The calculation of the design strength of the connection shows the adjustment of the mortar filling to be the best solution. However, the final design strength is low compared to the design strength of the concrete in the structural screed or the columns. This is the result of the horizontal tension in the structural screed, which reduces the concrete strength. A better result may be obtained by the removal of the structural screed at the connection and the placement of the concrete column directly on top of the steel beam. This adjustment needs a further research.
The conclusion is that the researched design in its current form is not effective enough to be applied in practice, but its drawbacks can be solved with a few adjustments to the design, making it an effective design solution. ... Read more