Due to increasingly efficient engineering of the last decades, the design process for civil structures is heading in the direction of optimal solutions. Among other things, the reduction in self-weight enhances the susceptibility to dynamic loads. As the process for the determination of realistic modal parameters from a digital model often diverges from the reality, the uncertainties should be investigated. This research aims to gain knowledge on the accuracy and stability of such modal parameter estimates. A case study is investigated to determine modal parameters for a realized tied-arch railway bridge. The desired modal properties include the natural frequencies, mode shapes and damping parameters. The frequency domain decomposition (FDD) method is applied on a set of accelerational measurements to determine the modal parameters. Four dominant frequencies are identified and investigated, from which the most dominant operational deflection shapes are extracted. The overall response of the structure shows great similarities with the expected mode shapes for similar bridge types. The computed modes show signs of complex behaviour, due to the characteristics of the load or the structure. An effective method to reduce uncorrelated noise is the application of an autocorrelation function (ACF) to the time domain signals, before execution of the FDD. Prior to the computation of the final results related to the case study, a simplified test case is considered to validate correctness of the FDD implementation.

The development towards a circular economy has many hurdles to overcome. For the construction sector an important step in this process is the transition towards reusing structural elements. Prefabrication of elements is a significant step towards achieving this concept. However, a case where both prefabrication and reuse are limited is the replacement of bridge decks. Headed bolts are welded to the steel supporting elements and encased in grout to connect them to the concrete deck elements. This method prevents reuse of the deck elements and hinders reuse of the steel supporting elements. Research and literature exists on a number of alternative shear connectors that increase the modularity of these elements. The best alternatives have a single limitation in common: the allowed deviation for the placement of the shear connectors and bolt holes is smaller than is feasibly possible. The variances of element placement during construction add up to make it incredibly hard for these low tolerance connections to be made. The bolt hole diameter can be increased to increase the deviation tolerances. The large nominal hole clearance this results in needs to be considered. This can be done by using either resin injected bolts or High Strength Friction Grip (HSFG) bolted connections. Using HSFG bolted connections is preferred due to the shorter time spent on site and minimal waste, but research on the subject is sparse. A proposed HSFG bolted connection that implements significantly oversized holes, defined as bolt holes with a nominal hole clearance roughly equal to the bolt diameter, and cover plates was designed together with both a control and regular connection to compare its behaviour with. The control connection is identical to the proposed connection with the exception of its holes which are normal sized. The regular connection has normal holes and does not include cover plates. Finite Element Models (FEM) were made of these connections that were subjected to static loading in a Finite Element Analysis (FEA). Test specimens of these connections were made and subjected to fatigue loading. The numerical results of the static FEA showed that the use of cover plates reduced the stiffness and slip load of the connection. The second observation was the small impact that the hole size had on the slip load when using cover plates. This small impact becomes negligible at design preload. The experimental results showed that the impact of larger bolt holes increased the loss of preload by roughly 1% during both short term relaxation and fatigue loading. The effect of the bolt hole size on the slip after fatigue loading was also concluded to be negligible, but the effect of the cover plates was concluded to be detrimental. It was overall concluded that the use of significantly oversized holes in HSFG bolted connections with cover plates is viable. The negative effects caused by the cover plates and required longer bolt make it preferrable for large disc springs to be used instead of thick cover plates. The viability of the concept allows for further research on the subject.

This research investigates how the current friction design standard should be improved, specifically for monopile sea fastening with polymers. Literature and results from tests performed previously to this research are investigated in order to obtain a complete overview of the factors that should be considered in the design standard. Additional tests are carried out on factors for which literature and previous test exercises are inconclusive. Friction test methods are compared to determine the best method for testing monopile sea fastening friction. The total test variability is analyzed to determine why safety measures are required. The validity of these measures is studied with a large set of test results. Finally, modelling as an alternative for testing is investigated.

In this thesis, the friction performance of polyurethane tensioner pads used in offshore pipe-laying was investigated. Tensioner pads are used in pipe-lay to create tension in a pipe. The need to understand the pads better is because of the increased use of pipe coatings and pipe lay in deeper waters. Deep water leads to more pipe tension, and polymeric coating reduces friction. A literature review was conducted on the friction of polyurethane. From the literature review, a few variables that influence polyurethane friction behaviour were summarised into the following research question: What is the influence of normal force on the pads, pad hardness, pad geometry, and pad temperature on the friction performance of polyurethane tensioner pads? Experiments were performed at a full-scale setup. Polyurethane has a nonlinear coefficient of friction, making it difficult to upscale results from laboratory testing. In the full-scale setup, existing pads can be tested to find the influence of the different variables from the research question. The test setup was found to be flawed. Not only did it deform due to the massive forces, but the data gathered from the hydraulic pressures was not robust and accurate enough to estimate the static coefficient of friction, which is important in tensioners. Therefore, only trends in the pad behaviour were observed. Increased normal force on the pads was found to increase the coefficient of friction. This contradicted the literature but was likely due to the geometry of flat pads versus round pipes, where the contact surface increased when the pads were loaded. Softer pads were found to yield higher friction than pads made from harder grades of polyurethane. This effect was also found in the literature. The influence of temperature was difficult to test. Since the pads could only be heated externally before testing, temperatures were inconsistent, and test results were inaccurate. The temperature did affect the friction significantly, though, so some newly produced pads were fitted with internal heating. Next to the experiments, different pad geometries were tested in finite element analysis. A new pad shape was found that decreased stresses, leading to higher friction. Next to the variables of the polyurethane itself, the relative humidity was recorded. The relative humidity changed significantly during the different tests, and it was found to affect friction more than anticipated. Three sets of new pads were produced for future testing to validate the influence of geometry and further investigate the influence of the pad temperature. Moreover, a new test setup was designed to test the coefficient of friction more accurately.

Nautical radar systems are subjected to random vibrations during their service life, which may lead to the degradation of the materials and a possible fatigue failure. Assessing the impact of these vibrations to the structural integrity of the radar is crucial for drafting appropriate maintenance plans and therefore, the development of a new tool is required, which will be capable of evaluating the fatigue lifetime of the radar system. This thesis examines a 5.7-meter-long radar antenna, supported by a lattice tower with a height of 20 meters, located in Rijkswaterstaat’s test environment in Stellendam. Although the lattice structure and the radar system are coupled, they are treated separately in this study. Firstly, a Finite Element Model of the tower is developed in ANSYS, where the radar is represented by an added mass at the top floor. The aim of the model is to identify the vibrations of the structure under the influence of the incoming wind. The stochastic description of the turbulent wind is taken into account in the evaluation of the wind loads and a random vibration analysis is performed, resulting into the response of the structure in the frequency domain. Furthermore, a second, simplified Finite Element Model of the radar system is built in ANSYS. Time series of the fluctuating wind velocity are generated and the wind load acting on the radar is approximated by the aerodynamic force in the along-wind direction, considering also the rotation of the radar antenna. In addition, the previously obtained response of the lattice structure serves as input for the radar model, representing the vibrations induced to the radar due to the motion of the structure below. The output of the model is the occurring stress response, which is subsequently used to assess the fatigue damage of the radar antenna. The results show that the development of stresses at the bottom surface of the antenna mainly occurs at its central area. Given the assumptions used throughout the thesis, the motion of the lattice tower is found to be the governing loading condition for the resulting stresses and the magnitude of the motion significantly influences the fatigue damage of the antenna. Finally, the fatigue lifetime appears to be very sensitive to the construction materials used for the radar system. These results should be verified by future measurements in order to improve the suggested models.

Unreinforced Masonry, a popular construction material with a rich historical legacy, has been resilient through centuries, despite its susceptibility to failure through various loading conditions such as seismic forces. Understanding the mechanical behaviour of masonry, particularly the cohesion and frictional mechanisms at interfaces between bricks and mortar, is crucial for assessing its structural reliability. This thesis presents an experimental study characterising masonry frictional interfaces using a tribometer test, a novel approach in masonry research. The study aims to investigate the frictional behaviour of brick-mortar interfaces under varying precompression levels and test frequencies (3 Hz and 0.2 Hz). A novel sampling method was implemented, wherein the required specimens were extracted from a bonded masonry couplet specimen. The couplets were bond wrenched and then subjected to a mechanical extraction. Bond wrenching, through tension, separates the couplets, thereby isolating frictional response from the influence of cohesion by decoupling cohesion between the unit and joint. A tribometer was chosen for the investigation of frictional parameters, tribometers are typically employed with metal surfaces and rarely applied to masonry. Consequently, experiments were conducted using a reciprocating tribometer, featuring a novel specimen extraction procedure and a modified setup. The novel extraction involved mechanically altering a parent brick couplet to extract compatible specimens. Customised holders were procured and used to accommodate the prepared specimen. The obtained specimens were then, fastened into the appropriate sample holders. Tests were performed on the specimen with displacement, tangential force, normal force and time being recorded. Three key parameters, the mean Coefficient of Friction (CoF), the Energy Coefficient of Friction (ECoF), and tangential contact stiffness were analysed from the collected data. The above mentioned parameters were evaluated through two approaches, (i) Mean Curve approach and (ii) Cycle approach. A mean curve is the averaged curve of the measured hysteresis loop, which encompasses the overall behaviour exhibited by the hysteresis loop. The experimental results revealed a dependency between the coefficient of friction and the applied pre-compression level, showing a non-Coulomb behaviour; this is in contradiction with assumptions of several models used for the analyses of masonry structures. Initially, experiments were conducted at a higher frequency (3 Hz) and followed by experiments at a lower frequency (0.2 Hz), and the results in both cases revealed a non-Coulomb friction behaviour characterised by a nonlinear connecting trend between kinetic and static friction region. The connecting trend between the kinetic and static region demonstrated a reduction in the degree of non-linearityan enhanced symmetry in the hysteresis profile as the precompression levels increased. The mean curve and the cycle approach yielded identical estimates for the coefficients of friction (CoF) and effective coefficients of friction (ECoF). The evolution of Coefficient of friction (CoF), did not exhibit any clear systematic time dependency, while Energy Coefficient of friction (ECoF) showed a systematic decrease over time. The ECoF related the energy dissipated by friction across each cycle to a hypothetical Coulomb energy dissipation. Therefore the ECoF captures the energy dissipation due to friction during one cycle, while the CoF captured the static friction region. The energy dissipation across different precompression levels were also studied and it was observed that the energy dissipation increased for increasing precompression levels. Tangential Contact stiffness refers to the tangential force required to effect a unit displacement in the tangential direction. The contact stiffness was calculated from the slope of the region of the hysteresis loop associated with displacement reversal. Contact stiffness was observed to increase with increasing precompression levels. This observation was also validated by the theoretical model which illustrates a proportionality between the applied normal load (precompression) and tangential contact stiffness. Additionally, the study highlights the impact of frequency on the observed frictional behaviour, noting more prominent static and kinematic components at lower frequencies due to reduced inertial forces. A preliminary study using the LuGre model was used to plot the analytically derived frictional force-velocity relationship, to briefly study the impact of sliding velocity on frictional force. It was deduced that the velocity had an influence over the frictional force at the interface. In conclusion, the findings provide valuable insights into the frictional characteristics of masonry interfaces under varying loading conditions. The results also shed light on the practical aspects of testing methods and offer considerations for further research in the field of masonry engineering.

To reach the Paris Agreement goals, switching from fossil fuels to renewable energy is inevitable. Wind power has proved to play a critical role in this transition. To speed up this transition, the wind industry must keep innovating. The major part of Wind Turbine Generators (WTGs) is installed by a jack-up which not only has its limitations from an engineering point of view, such as water depth, soil characteristics and lifting capacity but also from a financial point of view. To overcome these limitations, this research aimed at developing an innovative concept design for the installation of offshore WTGs. A vessel dynamic analysis showed that the Mighty Servant 1 is the most suitable Boskalis vessel to install WTGs from. The same dynamic analysis also highlighted that a motion compensation system is required to mitigate wave-induced dynamics and enabling WTG installation in floating conditions. After developing multiple concepts of motion compensation systems, a multi-criteria analysis in the form of an analytic hierarchy process is performed. It is found that the most promising concept should rely on hydraulic actuators. To find the optimal values of the design parameters of the chosen concept, a kinematic multi-objective optimization is carried out by means of a genetic algorithm. The optimal set of design parameters is selected by taking advantage of the Pareto front, which is computed by using three chosen performance indexes. A model is developed in MATLAB and Simulink to simulate the dynamics of the motions compensation system. The simulated results showed that a controller which uses velocity feed-forward and position feedback is the preferred way to go. The results also highlighted that the required amount of hydraulic power has a great impact on the economic feasibility of the system. Therefore, to reduce the hydraulic power and guarantee the feasibility, a passive system based on a hydraulic accumulator is added. Based on the results of this research, it can be concluded that the next generation offshore wind turbine generator can be motion-compensated with hydraulic actuators including hydraulic accumulators. Further research could be carried out by assessing more installation phases in combination with a wider range of load cases.

The offshore wind energy industry is quite literally reaching for the sky to meet the increasing demand for renewable energy in Europe. Offshore wind turbines are sprouting out of the waves off the coast of many European nations and their size is increasing rapidly. As the turbines become larger and the waters in which they are placed become deeper, the foundations that carry these behemoths must grow as well. The most frequently used foundation is the monopile foundation. Over the years, both the length and the diameter of these monopiles have steadily increased. Installing monopile foundations has, as a result of this, become more and more difficult. An important aspect of the installation of monopile foundations that has become more challenging is the upending of the monopile. When the monopiles are transported to the site of installation, they are sea-fastened to the deck in horizontal orientation. When they arrive, they need to be rotated to a vertical orientation for installation. This can be done with the aid of an upend hinge. This thesis focusses on the modelling of such a hinge for operability studies. The goal of these operability studies is to determine the weather and wave conditions in which the operation can be safely performed. Conventionally, the stiffness of the upend hinge is approximated by several linear springs between the vessel and the monopile. The aim of this thesis is to apply dynamic substructuring to existing Finite Element models of a hinge to more accurately describe its dynamic behaviour within hydrodynamic simulations. Hereafter, the response of the dynamically substructured model can be compared to the response of the conventional model. The findings of the research show that it is possible to use dynamic substructuring to reduce the Finite Element models of an upend hinge and implement them into hydrodynamic simulations of an upend operation. When comparing the conventional model to the substructured model, it can be seen that there is a significant difference between the high-frequency response of the models. However, the responses of the models to prevailing ocean waves are very similar. For operability studies, this response is most relevant. Furthermore, the required computation time is significantly higher for the simulations employing the dynamically substructured models than for the conventional models. Therefore, it is not recommended to apply dynamic substructuring to model this upend hinge in operability studies. For situations where the high-frequency response is more relevant, however, dynamic substructuring may prove a valuable tool to more accurately describe the dynamic properties of an upend hinge or other marine equipment.

The aim of this research is to increase the workability of a rescue craft launch and retrieval system on FPSOs in heavy sea states. Although a rescue craft’s purpose is to improve safety, multiple incidents recorded in the GISIS database have proven that the launch and recovery operation can be dangerous or even deadly. The problem research shows that the davit system is the main cause for incidents, which are related to design flaws, lack of maintenance and human errors, the three parameters for a successful launch. The opinion of the author is that a different type of launch and recovery system can lead to improvement of these three parameters and to an increased workability of the system. To compare a new design with the conventional design, a computational model of both designs is built in Matlab to simulate the launch of a rescue craft from an FPSO in various sea states. The conventional model shows dangerous accelerations in high sea states and the risk to collide with the hull of the FPSO. The concept design aims to reduce these motions and, in addition, provide a more redundant design with easy maintenance and focused on reducing human errors. After comparison, the concept design proves to reduce dangerous motions during launch and increase the workability in high sea states, while being very simplistic, robust and easy to operate. However, in the splash zone the concept model does not mitigate dangerous motions sufficiently. To further substantiate this conclusion, it is advised to further investigate the splash zone model and to develop a more detailed model of the concept design.

Bridges are exposed to dynamic forces – such as pedestrians crossing a bridge or the wind force acting on a bridge – which cause vibration of the structure. When a structure is forced at one of its eigenfrequencies it deforms into a corresponding shape leading to major deformations, which, in the worst-case scenario, can lead to collapse of the structure, as happened to the Tacoma Narrows bridge in 1940. It is thus very important to know the dynamic characteristics of a structure. For glass structures no specific limit values are defined, this is why it is interesting to investigate the dynamic behaviour of a glass bridge This thesis aims to predict the structural response of TU Delft’s Glass Truss Bridge when subjected to static and dynamic loads. The studied bridge is a footbridge, connecting the TU Delft campus to the Green Village, and is unique in the aspect that glass diagonals have been used in its construction. Through an iterative procedure of modeling, virtual testing and updating the model of the bridge, the dynamic response of the bridge is predicted. The study shows that the response of the bridge is between the European Guidelines’ limits for (steel) footbridges. Maximum acceleration of the bridge is found at 500mm/s and the lowest eigenfrequency is out of range of that of joggers. The sensitivity analysis shows that the parameters having the most influence on the bridge’s response are the diameter of the glass diagonals and the soil density. Using the outcome of the sensitivity analysis a dynamic testing protocol is recommended that outlines the optimal test setup for modal testing of the bridge. Through the simulated dynamic tests ten of the twenty eigenfrequencies of the bridge are found. For each of these frequencies, the damping is approach and modeshapes are reconstructed based on the imaginary plots of the Frequency Response Functions. The latter show a good correlation with the modeshapes obtained from the model.

Pile tip damage due to impact with an object (boulder) during the driving process of monopiles is of main concern in the offshore wind sector. Numerical modelling could accurately describe this failure mechanism and used as a tool in practice but also for the development of appropriate guidelines. In this research project, dynamic Finite Element Analysis is conducted in order to achieve modelling the driving and impact process and properly capture the response of the monopile.

The slip joint connection is a relatively new alternative method for connecting offshore wind turbine towers to prior installed monopiles. It consists of two overlapping conical sections that together form a connection. There are several challenges left to be solved before the slip joint can be applied on a commercial scale. One of those challenges lies in the decommissioning process of the slip joint connection. It is proven that build-up settlement can increase the friction force within the joint over its lifetime and complicate its disconnection. One potential method for reducing the friction force in the slip joint is the excitation of one of the structures shell modes localized around the slip joint. Good estimations of the shell modes of the structure are therefore essential. Models for precise estimation of the shell modes of a wind turbine with a slip joint are difficult and expensive to develop due to the complexity of the joint. This thesis is a study into the possibility of using simplified finite element models to estimate the shell modes of a wind turbine connected with a slip joint. This is done by estimating the shell modes of the structure using a reference model and seven simplified models in a modal analysis. The estimated shell modes are compared based on their eigenfrequency and mode shape. Based on this comparison, conclusions about the applicability of simplified models are drawn. The first 300 eigenmodes of the structure are estimated with both the reference model and simplified models. Of these eigenmodes, ten shell modes of interest are selected based on their eigenfrequency and location at which the modes are localized. The modes of interest are than compared for their eigenfrequency and mode shape. The mode shapes are compared based on the Modal Assurance Criterion (MAC), which is calculated at a specific location of interest. In addition to this, the angle in which the modes are orientated is measured and compared, as this can be useful information for the decommissioning process. Results showed that three out of seven simplified models studied resulted in a estimation of the shell modes which was sufficiently accurate. The simplifications used for these models consist of the averaging of wall thickness for the upper and lower slip joint and a simple model for the upper slip joint. From these results it can be concluded that some of the simplifications can be applied when estimating shell modes of a wind turbine tower connected with a slip joint, as they lead to only a small decrease in accuracy of the shell mode estimation. However, using these results to make predictions about other potential simplifications is challenging as each different simplification has a unique influence on the estimation of the shell modes.

Friction damping is common in engineering structures for the purpose of energy dissipation and vibration control. Examples of applications are bolted connections and earthquake isolation systems. However, there is a shortage of works that investigate the effects of different contact materials on the energy dissipation performance and friction behaviour of friction dampers, which is valuable knowledge for design optimization. This thesis uses a numerical approach to explore the time response and energy dissipated by friction of the harmonically excited SDOF (single-degree-of-freedom) system with Coulomb friction contact between the sliding mass and a fixed wall. In addition, for the same SDOF system, an experimental investigation of the friction damping performance in terms of friction behaviour and energy dissipation is carried out for (1) steel, (2) rubber and (3) aramid contact materials. The aim is to get a better understanding of how different contact materials affect the performance of friction dampers. Various time scales, excitation frequencies and friction forces are considered. The main findings of this research are: (1) the characterization of the friction behaviour of steel-to-steel, rubber-to-steel and aramid-to-steel contacts; (2) the comparative analysis of the energy dissipation performance of the different contact materials; (3) the assessment of the long-term performance of the different contacts; (4) the comparison between numerical results based on the Coulomb friction model and experimental results. The tests have shown that rubber has the highest energy dissipation capacity and fairly unstable behaviour, steel has the second highest energy dissipation and irregular behaviour and aramid has the lowest energy dissipation performance and very consistent behaviour. Finally, the application of a method that calculates the energy dissipation of friction damping based on direct experimental outputs is an important contribution to the field regarding experimental investigations.

The Circular Arch Bridge is a pedestrian bridge consisting out of four different recycled materials: cast glass, ceramic, circument and geopolymer concrete. Due to an increasing amount of vibration problems in modern pedestrian bridges they should not only be designed for static loads, but dynamic loads have to be considered as well. There are currently no guidelines in the Eurocodes for the dynamic assessment of a bridge like the Circular Arch Bridge. Therefore, this paper provides a research on how the dynamic assessment of the Circular Arch Bridge should be conducted. The Circular Arch Bridge is considered a dry-stacked masonry arch bridge. A full dynamic assessment is conducted, with the use of finite element software, according to the guidelines for pedestrian bridges. The eigenvalues of the Circular Arch Bridge are not within the critical range for pedestrian induced dynamic loads. It is found that for everyday use the Circular Arch Bridge is within Comfort Class 2 from the Eurocode, thereby providing a medium comfort level. A special load case is added to the analysis representing a group of 60 people dancing on the bridge during experimental testing of the bridge. For this load case the Circular Arch Bridge is within Comfort Class 3 from the Eurocode, thereby providing a minimum level of comfort. With a sensitivity analysis it is determined that the most sensitive input parameter of the finite element model is the modulus of elasticity of the interlayer. An investigation of the effect of large stiffness differences between the interlayer and the stones on the dynamic properties of the bridge is conducted. It is concluded that the large stiffness differences have a positive effect on the dynamic properties of the bridge. The effect of the dry-stacked assembly of the bridge on the dynamic properties is also investigated. This as a negative effect on the dynamic properties of the bridge.

Two-bladed offshore wind turbines regained interest in finding the most profitable way of generating wind energy. Wind industry companies demand the safe operation of two-bladed offshore wind turbines. To guarantee safe operation, the companies perform operational modal analyses to investigate modal properties variation which might be allocated to damage. However, the operational modal analysis of an operative two-bladed offshore wind turbine faces multiple challenges. (1) Fundamental operational modal analysis assumptions about the applied loads are violated by environmental and operational loads. (2) The closely spaced modes of an offshore wind turbine are hard to identify. (3) An operative two-bladed offshore wind turbine is a linear time-variant system. This paper introduces an enhanced operational modal analysis procedure to overcome some of the mentioned challenges. The enhanced procedure incorporates a post-processing technique in a transmissibility-based approach. A developed representative model of an operative two-bladed offshore wind turbine is used to compare the enhanced procedure with the frequency domain decomposition method. Based on the comparison, this paper proposes a new operational modal analysis method that combines a transmissibility-based approach, the post-processing technique, and the frequency domain decomposition method. This paper proves that this proposed combined method is a promising new operational modal analysis technique that outperforms the enhanced procedure and the frequency domain decomposition method in identifying the modal properties of a two-bladed offshore wind turbine.