The goal of this research is to assess technical and economic feasibility of hydropower at the weir-complex of Driel. A local initiative opting to improve the environment gained interest in the idea and asked Arcadis NL for help. The weir complex at Driel lays in a key position in the Dutch river Delta and regulates the flow to the IJssel and Nederrijn, both important parts of the flood protection and important shipping routes. In the Nederrijn 2 other hydro-power plants have been built at weirs. Driel was considered as well, but at the time could not be made feasible due to the low head difference at Driel. Developments in low-head hydro-power have given new possibilities and reason for reassessment. First the location has been analysed, in particular the flow situation. Except for the low head difference, the location lends itself well for a hydroelectric plant. The crux of the research is therefore in making the most of the available head. 4 variants have been worked out: a copy of the downstream hydro-power plant of Maurik as a reference, several variations on low head Kaplan turbines and an Archimedes screw have been assessed. A special variation of the Kaplan is the Venturi enhanced Kaplan, which uses part of the discharge to increase the head difference over the turbine. To estimate the annual production, first a simple approach, assuming a turbine can create a certain head difference, and later a hydraulic model incorporating hydraulic losses and using turbomachinery theory, has been used for the Kaplan design variants. The result of the comparison is that the regular Kaplan variant number 4 with 5 turbines, a combined capacity of 3.160kW and a LCOE of 0,154 € per kWh (using interest rate of 3,3%), has the best economic performance and is therefore recommended for further development. A good second option with a lower initial investment (9,6 million euros versus 20,5 of variant nr. 4) is design variant number 1 with a set of 2 Kaplan turbines having a combined capacity of 1.475kW and a LCOE of 0,161 € per kWh. Despite the regular Kaplan performing better economically, the Venturi Enhanced Kaplan Turbine certainly has potential for low head run of river hydropower and is therefore recommended for further research as well. The increase in power and produced energy gives reason to believe that further optimisation and detailing will lead to a competitive design compared to the regular Kaplan turbines.

There is a growing demand for renewable sources of energy of which wave energy conversion is one. The Ocean Falls is an oscillating water column (OWC) system invented by BAM Infraconsult b.v. This system differs from conventional OWC systems since it includes a connection tube and an adjustable back wall. The OWC system is a resonance system for which maximum efficiency is obtained once the natural frequency matches the incoming wave frequency. This thesis focusses on the modelling of the OWC system with ANSYS AQWA and ANSYS Fluent. A parametric model and a CFD model are developed to assess the performance of the OWC system. An optimum is sought for in terms of system performance, constructability and cost effectiveness. Eventually a conceptual design of the Ocean Falls OWC system is made to assess the technical- and economic feasibility.

The focus of this research was the implementation of a permanent steel fibre reinforced underwater concrete floor (SFRUCF) as a permanent structural floor. A model was created that can describe the soil structure interaction of an SFRUCF including the highly non-linear behaviour of SFRC. The soil structure interaction of the UCF was modelled in Plaxis 2D with a plate element that includes the behaviour of SFRUC by means of an MN-κ diagram. This model was validated with measured data from the Albert Cuyp garage. It was shown that due to the uplift pressure heave occurred in the clay layer underneath the UCF, which increases the load on the UCF by 10%-30% and should be taken into account in the design. Also the heave from the deep Eemclay was considered. This heave had influence on the total deformations but hardly affected the internal forces in the UCF, justifying the fact that this heave is usually not included in the design of a UCF. A fictive E-modulus is often used to describe the cracked behaviour of steel fibre reinforced concrete. It was shown that using this fictive E-modulus in the building phase leads to an underestimation of the shear forces.
Additionally, a sensitivity analysis was done to show which parameters influence the calculation results, the design and the suitability of a permanent SFRUCF. The suitability of an SFRUCF is determined by the column loads in the final phase and the presence of a stiff raft. It was concluded that an SLS check should be included in the CUR 77 for water tightness, crack width and deformations if an SFRUCF is to be used permanently. The interaction between the raft can be modelled in Plaxis 2D with the plate element that has the behaviour of SFRC. For cases that do not include a stiff raft simpler models can be used such as the Plaxis model with springs or even a beam model with SFRC input.

Durban is the third largest city of South-Africa, located in the province of KwaZulu-Natal. The city suffers from severe floods from time to time, finding its cause in both the Indian ocean as well as the Umgeni river. The eThekwini municipality wishes a better insight in the occurrence of these floods and searches for a structural solution to protect the coastline. The eThekwini municipality has models in operation to predict the hydraulic characteristics in the ocean and the river. However, the existing models don’t represent the reality sufficiently, since the interaction between the Indian ocean and the Umgeni river is not modelled properly yet. An analysis on the area of interest has been executed. The conclusion was drawn that the Umgeni river delta was (partly) tide-dominant, meaning that the Indian ocean imposes the downstream water level. Furthermore, the wave climate was observed, as well as a look into present coastal protections. The link between the Indian ocean and the Umgeni river has been modelled using Delft3D. Since the Indian ocean imposes a downstream boundary condition (in terms of a water level) for the Umgeni river, a backwater curve might occur. First, the link is made by extending the Delft3D-model which was present for the Indian ocean only. The model has been extended all the way up to the Inanda dam. The part of the river included in the new model is approximately 32 푘푚 long. When comparing the models output at the river mouth, at the same location as a measurement point, similar behaviour can be observed. The same phase (lag) is observed, contrary to the tidal range. The tidal range in the model differs from reality, but this is due to a lack of calibration in the amplitudes of the different tidal constituents taken into account. Hence, the renewed model seems to work, but more validation still has to be done. This was not possible yet, as there is a lack of measurement stations along the river. Next to an extension of the Delft3D model, a script has been written in Python. This script is based on the empirical fit of Bresse and shows an elegant function. The results from the function in Python and the model in Delft3D are similar in a qualitative and a quantitative way. Both the models show an influence of the Indian Ocean, reaching easily to about 12 푘푚 upstream of the river mouth. This can be explained by the mild bed slope in this part. A structural solution for the flooding on the promenade at the height of North Beach was found in the form of a seawall. The most important design demand is to protect against a high water level of a 200 year return period combined with a 50 year return period wave height. These storm conditions are input for the ocean-river model, which delivers wave characteristics at the beach front, linking the structural design to the ocean-river model. After a pre-selection on design options, a Multi Criteria Analysis is carried out for the remaining eight design options. Grading is done based on criteria, representing the viewpoints of the many stakeholders involved and leading to a highest grading of a seawall in combination with an emergency barrier. Following, the water-retaining height for a vertical wall is determined. Given the the ground level height of the promenade to be 푀푆퐿 + 2.2 푚 and a total water-retaining height of 푀푆퐿 + 2.944 푚 this leads a practical construction height of 0.80 푚. Due to the limited height a reinforced concrete seawall is designed with emergency barriers for the beach entrances. The emergency barriers are designed of pinewood. Additionally, in order the fit properly in the surroundings, an integrated design is added with features like benches, thatch umbrellas and plants to disguise the construction and protect the Golden Mile in style.

During the past decade, durability and sustainability has become more and more important in the building industry. By using no steel reinforcement, which has with high carbon emission and is sensitivity to corrosion, the structure should have a longer life span with less maintenance and a lower carbon footprint.
To get more information on unreinforced concrete structures, a literature study is done, focused on old Roman structures made out of Roman concrete. Besides historic concrete, research is also done on modern concrete and its capacity.
The new bridge is designed for the "Hoofdvaart", a canal in the polder called, "Haarlemmermeer". The design consists of three arches are connecting the two abutments and two piers. In the connection of two arches, above the piers, so called flood openings are placed. Romans used flood openings to let water pass, but in this case they are used for the reduction of weight. Wooden piles form the foundation to the stiffer sand layers. Calculation of the design is done in a few steps. Firstly, the original design, as explained above, is calculated. Results show stresses, that are more than 7 times higher than the capacity of the concrete. The biggest contribution to the stresses are coming from self-weight and load model 1. Load model 1 is a heavy vehicle placed at the most unfavourable position of the bridge. Lowering self-weight is an option, but load model 1 has fixed values, so they cannot be lowered. Next, six optimizations are designed and calculated to create a structure that should fulfil the requirements. It turns out that the structure still exceeding the capacity by approximately 28%. After these optimizations can be concluded that for the given location, this design is not totally satisfying. To find out what contribution soil has to the structure, a few extra calculations are done for the last optimization. Based on overall calculations, the conclusion is that the top soil layers of the "Haarlemmermeer" are not capable of generating enough horizontal support for the unreinforced bridge. To finalize the design, a cost analysis and Life Cycle Analysis, LCA, are made. In both analysis a comparison is made between the new design and a reinforced bridge over the "Hoofdvaart" in "Nieuw-Vennep". The cost analysis show a difference of approximately "170.000,- in advantage of the new design. Especially the material costs of steel and pre-cast elements in the existing bridge, contribute to this difference. So an unreinforced structure has less labour and less material costs, compared to a reinforced structure. Of course this difference is also depending on the type of structure and the design. The LCA shows around 30% less carbon emission for the new unreinforced bridge, compared to the existing reinforced bridge. Especially material use and demolition contribute to this decrease. This shows that an unreinforced structure is 30 to 40% more sustainable than a reinforced structure.

Nowadays, precast technology is mainly used for the production of concrete shell elements. Computer Numerically Controlled (CNC) milling techniques is the main production method of single or double-curved concrete elements, creating astonishing shapes with high accuracy. However, these techniques are also accompanied with high costs and large material waste. Skilled carpentry or curved steel formwork are other techniques used for the production of concrete shells. An alternative to the aforementioned techniques is the “Flexible Mould” method being developed at Delft University of Technology. This method is based on mass customization of the produced panels, due to the adaptability of the formwork's shape according to the specified geometry. The concept of the “Flexible Mould” will be used as a starting point for the current thesis.

Concrete shells are mainly used for decorative reasons such as claddings and facade elements. Their structural capacity has still to be improved so that they can be applied as load-bearing elements and avoid sub-optimal or even “bad” designs. Several researches are being conducted in order to analyze and improve the load bearing capacity of concrete shells produced with the adjustable formwork technique. Applying conventional steel reinforcement to take up possible occurring tensile stresses in concrete shells produced with the Flexible Mould, has been proved to be possible only with limited diameters due to construction requirements.

In the first part of the thesis, a research was conducted on possible improvements in the production of concrete shells with the flexible mould, so that they could be considered feasible to be applied in real life structures. Having conducted a literature review on production parameters related to the “Flexible Mould” concept, Computer Aided Design (CAD) was used as the main tool to create the digital geometry of double-curved concrete elements. Dimensional limitations imposed from the existing test set-up of the adjustable formwork at TU Delft laboratories, as well as the inherent geometry of shell elements, had to be taken into account. As a next step towards the implementation of double-curved concrete elements in real life structures, non-load-bearing laboratory tests took place. These tests were performed for illustrating reasons with sand to be the main material used instead of concrete. During these tests, a steel wire mesh diamond shaped was applied as the elastic layer of the flexible mould, being a different material in comparison with the previous studies on the flexible mould. Grid distance between the actuators was the main parameter investigated during this part of the research.

In the second part of the thesis, a study was conducted on possible improvements in the flexural tensile capacity of concrete shells via prestressing steel reinforcement. CAD design and Finite Element Modeling (FEM) were the main tools used. Due to shell's complex geometry, the research was conducted first for simple geometrical shapes under linear static analyses. Two and three dimensional elements were investigated being modeled as plane stress elements and solids respectively. Linear or single-curved prestressed concrete elements were analyzed with regard to their deflection and stress field. The number of concrete elements as well as the influence of an intermediate element in-between them simulating a joint, was an additional investigated parameter.

Subsequently, a four-point bending that will take place at TU Delft, was simulated with Finite Element Modeling (FEM), investigating its structural response under both linear and nonlinear static analyses. The created (FEM) comprises of two centrally prestressed concrete elements connected with a mortar joint in between them. No bond interaction between the post-tensioning steel reinforcement and the concrete is incorporated in the FE model. The type and size of the applied reinforcement is investigated in this model. The main goal of this part was to analyze the structure's response for loads exceeding the cracking load of the concrete, taking into account a brittle concrete failure at joint's location.

In the final part of the thesis, a post-tensioned arch structure segmented in a series of concrete elements and joints, was first designed with CAD software and then analyzed under a linear static analysis via FEM. Although more complex, a three-dimensional (3D) modeling was conducted, aiming at describing the three dimensional state of stress and deflection field of the arch. Based on a draft CAD model, several geometrical parameters had to be adjusted in order to meet construction requirements of the final concrete shell structure. Modeling and meshing requirements imposed from the Finite Element Analysis (FEA) software were also taken into consideration for the final shape of the arch.

The current thesis is a part of a research program that is being performed at TU Delft, aiming at developing the Flexible Mould with regard to construction and structural application of concrete shells in real life structures.

The Dutch Delta Approach has been set up with the aim of ensuring water safety in the Netherlands and improve it where necessary. The open connection of the Nieuwe Waterweg has become the subject of debate. So far, the Dutch Delta Approach do not take closure of the Nieuwe Waterweg into account. A group of six engineers do anticipate on the closure of the Nieuwe Waterweg and have prepared a scheme for that purpose, called: Plan Sluizen (or Plan Spaargaren). The closure scheme includes provision of navigation locks and a discharge complex. Focus of this report will be on the development of and checking the technical feasibility of the design for a flexible discharge facility in the closure.
At present a part of the river Rhine water is discharged through the Nieuwe Waterweg to the North Sea. Since the water cannot be rerouted, a discharge facility must be included in the closure complex.
First, the Nieuwe Waterweg, as a part of the Rhine-Meuse delta has been analysed and the effects of climate change in this area have been mapped out. Subsequently the report zooms in into the closure, lock and discharge complex that has to be constructed in the future. The two most important requirements are: the closure must be able to withstand the normative water level at sea, including expected sea level rise; the discharge complex must be able to discharge a 20% of the normative Rhine discharge at every random moment.
Looking into the location of the closure and discharge complex went hand in hand with deciding whether to construct one large complex accommodating all components at one location, or to divide the components over two locations. A location for all the components together would be positioned in the Nieuwe Waterweg. When dividing the components of the closure complex, the two locations to be considered are somewhere in respectively the Oude Maas and the Nieuwe Maas, close to the Beneluxtunnel.
A discharge method using Venturi was chosen. Venturi tubes can be used in natural flow conditions, driven by a water head, and improve the efficiency of pumps constructed into the Venturi tube. In future there will be a time when the natural water head has become too small, due to sea level rise, to discharge the required amount of water. The discharge sluice will be changed into a pumping station.
It turns out that 72 pumps are needed with a capacity of 50 m3/s for normative river discharge conditions in 2100. For the normative discharge in 2018 no pumps are needed. For average river discharge, coinciding with storm surges, discharge using the natural water head is possible up to 2100.
The dimensions of the discharge structure were determined. The structure will be adaptable by using different modules in the centre piece of the Venturi tubes.
After determination of the overall dimensions the stability of the structure has been checked. Concrete calculations have been made to check the concrete dimensions of the main parts of the discharge structure.

The present thesis has the objective to create a procedure for the automatic preliminary design of reinforced concrete structures, based on the Evolutionary Structural Optimization method (ESO). The developed algorithm performs heuristic topology optimization based on multiple criteria, in subsequent optimization cycles executed in series. In each ESO cycle, it is possible to perform material addition, removal or transition between a couple of materials, i.e. steel, concrete and void. Each optimization cycle is governed by an optimality criterion chosen from: stiffness, Von Mises, Drucker-Prager, tension stress criteria or linear interpolation of previous ones. The finite element analysis used in the algorithm regards all materials as linear elastic. The reaching of maximum strength and failure of materials is not taken into account.

The automated design process of reinforced concrete structures has been separated in two problems: the form-finding of reinforced concrete structure as a whole and the definition of internal distribution between steel and concrete. The first problem is solved, in the first optimization cycle, with a ``standard'' ESO procedure, with the only difference in choosing a Von Mises optimization criterion over a ``classical'' stiffness criterion. The second problem is solved, in the second and third optimization cycles, combining in series two additional ``modified'' ESO procedures and introducing gradual transition in optimization criteria through linear interpolation of sensitivity numbers. The combined criteria for the second cycle are a Von Mises and Drucker-Prager optimization criteria, while for the third cycle, a Drucker-Prager and tensile stress optimization criteria. Moreover, additional geometrical constraints are applied, to ensure a set minimal distance between steel and outer boundaries, i.e. concrete cover, and to ensure optimal angle preservation for steel members found during optimization, introducing two new ``density'' matrices called \emph{cover} and \emph{mask}.
Summarizing, the preliminary design of reinforced concrete structures is dealt with three cycles of ESO optimization procedures executed in series, with optimization criteria that gradually change with continuity between the different cycles over the whole process.

The developed procedure has been tested on several case studies, both from ESO and reinforced concrete literature. The defined ESO process has been found to generate solutions with steel correctly placed in tensile stress zones both to resist bending and shear. Generally, the presence of remaining tensile stresses in concrete zones in the solutions is absent or very limited, and in latter cases their magnitude is very small compared to other stresses.
Obtained solutions cannot be directly used as such for reinforcement layouts definition but, in combination with principal stresses plots and engineering judgement, they are able to suggest useful resulting reinforcement layouts.

As result of the specificities introduced for addressing the design of reinforced concrete structures, the ESO method has been extended for the case of topological optimization of composite materials with macro structure, with different optimization criteria applied to component materials, with one component material that has different resistance in tension and compression and with geometrical constraints for one component material.

The complete MATLAB code is published in the annex.

When engineers at Tunnel Engineering Consultants (TEC) used the Eurocode 2 (EC2) for the verification of flexural cracks in cross sections of immersed tunnel elements, they found out that there was more reinforcement needed for crack width limitation than for tensile strength of the reinforced concrete. This raised questions, namely whether the extra reinforcement is needed, how accurate the EC2 calculates the crack width and what the influence is of the construction height on the crack width?

Are the current rules in the Eurocode 2 for the calculation of flexural cracks too conservative for large thicknesses that are applied in the concrete lining of immersed tunnels?

In this thesis the crack width calculation of the EC2 has been compared with other codes around the world. When these codes are compared with each other it seemed to be that the EC2 is not conservative in comparison with the other codes, however it does not directly mean that this is true.
To check whether the codes, especially the EC2, are conservative, the codes should be compared with laboratory experiments. Since there is little data of experiments available where the cracks are carefully measured, in particular beams with large thicknesses, the finite element program DIANA is used to gain more data sets. A DIANA model is validated with three different experiments with each a different height.

When the EC2 and the DIANA results are compared, a few differences are found. The predicted crack widths in the EC2 are larger than that of the DIANA results. In the EC2 the crack width is the multiplication of the crack strain and crack spacing. If these values are compared, the EC2 gives a smaller crack strain than DIANA and therefore the crack spacing gives an even larger difference than the crack width. Next to that, the influence of the parameters in the EC2 is analysed. In both the EC2 and the DIANA results the cover is the most important parameter for the crack spacing and the steel stress of the reinforcement is the most important parameter for the strain. In all the results there is almost no effect of the construction height visible, except in the crack strain of the DIANA results when the cover is relatively large. A decrease of strain with an increase of height has been detected.

The differences in crack strain can be explained by the fact that the strain in the EC2 is calculated at reinforcement height, but the strain at the outer fibre is needed. In axial loaded cases these strains are the same, but in cases where the cracks appear due to bending moments, which is the case in this thesis, the strain is bigger at outer fibre. Next to that it seemed that influence factors used in the crack spacing calculation are overestimated, but no clear reason is found for this result.

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

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

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

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

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

The demand for offshore wind farms is developing rapidly due to the increased demand for renewable energy. Installation of foundation piles for offshore wind, however, are accompanied by a serious by-product which is the high underwater noise levels emitted during the pile-driving process. Current mitigation methods have proven to decrease the underwater noise emission, but these methods come at high costs. Moreover, these methods do not reduce the noise generation, but mitigate the noise that is already radiated into the water column. This study investigates a new concept, namely the reduction of noise at its source by altering the waves as they propagate downwards the pile.

This thesis is a study on the cracking behaviour of road bases constructed with cement bound reclaimed asphalt (also known in the Netherlands as AGRAC). It is decided to focus on this material because of the few researches available on the topic although the material being widely applied, at least in the Netherlands. The
goal of adding cement to the recycled asphalt aggregate is primarily to increase the resistance to permanent deformation (rutting). But, as in all cement-bound materials, in the AGRAC base layer shrinkage cracks might occur which could reflect through the overlying asphalt layers. Because of this, during the last decades the cement content was reduced from the initial 4-5% down to 2-2.5% (by mass).
In order to study the cracking behaviour of AGRAC, in this research one grading and two cement contents (2% and 4% m/m) are considered. A series of tests is performed to evaluate the properties of the two AGRAC mixes at different values of curing time (up to 130 days) and 3 different temperatures (0, 15 and 30°C). The dependence on the curing time and temperature are considered because of the presence in the mix of cement and bitumen respectively. In particular the tests performed are: indirect tensile strength, modulus of elasticity, shrinkage, thermal deformation, Poisson’s ratio and relaxation. The mechanical properties retrieved from these tests are used as input in a model which predicts the occurrence of cracks in an AGRAC base. If cracks occur, the model characterizes the crack pattern in terms of time of occurrence of the cracks, crack spacing and crack width. The calculations are done in two cases: non-weakened (plain) and weakened (with joints) base.
From the laboratory tests performed a dependence of the mechanical properties of AGRAC on the material temperature is clearly visible. Interesting results are also derived from the model, which shows the influence of the time of construction of the base (the worst scenario is observed for construction in August) and the difference in the cracking behaviour between the two AGRAC mixes (2 and 4% cement m/m). It is observed that the AGRAC mix with 4% cement leads to a higher risk of cracking compared to AGRAC 2%. In the worst scenario of base with AGRAC 4% constructed in August many crack series occur with a very close final crack spacing. The model shows how in this case even applying saw-cuts in the base is inefficient in terms of controlling the crack formation process.