Many steel bridges in the Netherlands, built in the 1950s and 1960s, are nearing the end of their service life, with steel bridge decks suffering from fatigue damage due to high traffic loads. Replacing these decks with Glass Fibre Reinforced Polymer (GFRP) Web-Core Sandwich Panel (WCSP) decks is a potential solution due to their superior strength-to-weight ratio and better in-plane fatigue performance.

A critical aspect of using these bridge decks safely is verifying the fatigue life of the Web-to-Flange Junctions (WFJs), which connect the webs to the facing. Fatigue damage is known to occur in such components with changing cross-sections, leading to stress concentrations. Current design codes lack verification equations or S-N curves for this component, necessitating further research.

This research investigates the static an fatigue performance of the WFJ by performing tests and identifying key parameters influencing this response. Through testing, the static bending moment resistance and the dominant failure mode are determined. Using the safe life approach, an S-N curve is generated by measuring the number of cycles until crack initiation occurred during cyclic loading.

Static tests revealed a constant rotational stiffness followed by a significant reduction due to delamination. Fatigue tests showed progressive stiffness degradation and crack propagation, with some crack retardation indicating a stabilisation phase before ultimate failure. Finite Element Modelling (FEM) accurately predicted initial stiffness but overestimated post-crack rotational stiffness, suggesting the need to incorporate additional parameters like material stiffness degradation or cohesive zone modelling.

This research identified important parameters such as waviness, web thickness, and radius affecting the response of the WFJ. However, testing did not confirm the predicted linear relationships between web thickness, radius and moment resistance as suggested by equations given by Lekhnitskii. Additionally, no direct correlation was found between waviness and moment resistance. It was observed that specimens with greater web thickness often also had higher waviness, and it is hypothesised that these parameters influence each other which would explain the non-linear relationship found from testing. Future research is needed to verify this hypothesis and include methods for quantifying the 'waviness' parameter.

This research enhances the understanding of the static and fatigue behaviour of WFJs in GFRP Web-Core Sandwich Panel bridge decks. The findings reveal that the dominant failure mode of the WFJ subjected to bending is delamination, due to out-of-plane stresses, as predicted by equations given by Lekhnitskii. Therefore, it is suggested that future design codes for FRPs incorporate these equations and delamination S-N curves to verify the fatigue safety of this component. Additionally, the WFJs were observed to be damage-tolerant, suggesting the potential for alternative design concepts to the fatigue life approach. Static tests revealed that although increased web thickness enhances the strength of the WFJs, it is also correlated with increased waviness, which is found from previous research to reduce strength. Future research could explore acceptable levels of crack growth and rotational stiffness degradation for safe bridge design, contributing to the development of design guidelines for GFRP WCSP, making it more viable to use these bridge decks in bridge renovations. ... Read more

Fiber Reinforced Polymer (FRP) has increased rapidly in popularity in the past few decades. The material's advantageous properties, such as a high strength-to-weight ratio and low required maintenance, gave rise to its popularity in multiple major engineering branches. Buckling behaviour develops due to the notably low stiffness-to-strength ratio and the usual high slenderness of FRP plates. The occurrence of initial imperfections increases the tendency of the material to buckle. The load-carrying capacity of structures with post-buckling behaviour can be determined with progressive failure analysis, which requires a damage model that characterises the onset and evolution of damage. In Abaqus, the Hashin damage model is implemented by default, which considers the four failure modes of the material. Numerical analysis of strain-softening materials with local damage leads to deformation localisation in a single element: a finer mesh will decrease the amount of energy dissipated. To prevent this localisation into arbitrarily small regions, the stress is related to the deformation of a finite volume. The damage evolution is described with a stress-displacement response instead of a stress-strain response. The energy needed to open a unit area of the crack, the fracture energy, is defined as a material parameter and depends on the mesh size of the model. The assessment of fracture energy properties in composite materials is challenging due to specimen geometry and fibre lay-up, and accurate data of GFRP fracture energy is largely unknown. When no actual post-failure behaviour is acquired, the lower bound fracture energy can be determined from the material properties. Numerical analysis of uni-directional coupon experiments is performed to determine the input values and response of the lower bound fracture energy. The lower bound fracture energy implementation results in an abrupt drop in stress when the material strength is reached. Increasing the lower bound fracture energy by a minimum of 2% prevented numerical inconsistencies. Progressive failure analysis of multi-directional coupon experiments validated an increase of 10% for the lower bound values. The use of lower bound fracture energy for non-linear buckling analysis is verified with progressive failure analysis of the buckling experiments. The lower bound fracture energy, increased by 10%, approximates the ultimate strength of six tests with an average difference of 7.7%. To analyse the non-linear buckling behaviour of a GFRP plate, a buckling curve is created by varying the plate thickness. The influence of geometric imperfections on a plate's buckling strength is studied by applying different initial imperfections. Two types of boundary conditions are used to analyse if they result in a different buckling curve. A difference in the buckling strength reduction factor of 0.1 is found. Initial imperfections reduce the buckling strength of the material, which is most apparent for plate slenderness around 1.0. An initial imperfection of B/125 resulted in a 40% strength reduction compared to the elastic buckling strength. The average difference in reduction factor between an initial imperfection of B/1000 and B/125 was 16%, with a maximum difference of 26%. ... Read more

The increasing use of Fibre Reinforced Polymers produced by Vacuum Assisted Resin Transfer Molding in civil infrastructure applications leads to the need for an appropriate research data. The VARTM produced structural elements are not limited in dimensions and material properties and typically are slender structures parts of which are susceptible to plate buckling. The latest standards - CUR96 Vezelversterkte kunststoffen in bouwkundige en civieltechnische draagconstructies and JRC Prospect for New Guidance in the Design of FRP – are for a large part based on the research data of pultruded profiles and in terms of design for buckling, focus on the flange / web interaction. The goal of this thesis is to investigate the effect of initial out of plane deformations on buckling of FRP plates produced by VARTM. ... Read more

Floating bridges are found at locations where deep water must be crossed for a long distance, such as in Norwegian fjords. The superstructure of the existing floating bridges is usually constructed from steel. In a marine environment these bridges are exposed to dynamic wave loads. As such, the current floating bridges suffer severe damage due to corrosion and fatigue. Using fiber reinforced polymer instead of steel could alleviate these phenomena and reduce maintenance costs. However, the lower stiffness could cause undesired vibrations in the floating bridge. Therefore a parametric model is developed to investigate the influence of design parameters on the dynamic response of a floating pontoon bridge.

A literature study is performed to find suitable concepts and techniques to develop the floating bridge model. A floating pontoon bridge can be schematized with rigid bodies, Euler-Bernoulli beam elements and linear springs and dashpots. The fluid-structure interaction is taken into account by including the added mass, hydrodynamic damping, hydrostatic stiffness and wave force transfer functions of the pontoons. A frequency domain approach is used to compute the dynamic response.

A parametric model of a floating pontoon bridge to predict the dynamic response is developed in Python. The hydrodynamic properties of the pontoons are computed by Diffrac and are used as input for the Python model. The Bergsøysund bridge is used as a reference case, because measurement data of this bridge’s dynamic response is available and can be used for validation.
The geometrical and structural properties of the Bergsøsund bridge are used to model its dynamic response. Wave conditions with a peak frequency at 2 rad/s are used. The results show that the response of the pontoons is governing compared to the response of the superstructure and that the dominant degree of freedom is sway. The fourth sway mode is the main contributor to this dynamic response. A comparison with measurement data shows that the produced response spectra are in good agreement with the measurements in terms of the peak locations.

In the parametric study the influence of single design parameters on the dynamic response of a floating bridge is investigated independently. The results show that the length of the superstructure has the biggest influence on the dynamic response of the floating bridge. In general, a reduction in stiffness in the superstructure leads to a lower overall frequency response function and thus to a lower dynamic response. Increasing the stiffness or reducing the mass of the bridge shifts the eigenfrequency of the fourth sway mode to a higher frequency and vice versa. Finally, when the damping is increased, the peaks in the frequency response function decrease and thereby the dynamic response in resonance reduces.

In conclusion, the dynamic response of a floating end-supported pontoon bridge is mainly influenced by the stiffness of the superstructure. A fiber reinforced polymer superstructure should be designed sufficiently stiff, especially in lateral direction, to keep the overall frequency response function low enough.
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