The use of Glass Fibre-Reinforced Polymer as a building material in structures or structural components is on the rise. Standards such as CUR96, DNV and JRC provide a basis of design with the material. However, there is a lack of confidence in the design phase with structures made of Glass Fibre-Reinforced Polymer, resulting in the use of large safety factors causing the components to be bloated in size. At the time of writing this report, the technical committee, CEN/TC 250 (responsible for developing structural Eurocodes), establishes a technical design specification for Fibre-Reinforced Polymer (FRP) structures. This technical specification describes a simplified and linear criterion to determine the capacity of a GFPR Laminate, in addition to being open for the use of Progressive Failure Analysis (PFA). However, the simplified and linear criterion is overly conservative, whereas there is a lack of faith in the use of the PFA considering the failure theories and degradation models that are currently in use. This report discusses the PFA, a non-linear, 5-step, advanced 2D analysis model, that can predict the static strength of in-plane stress dominated Glass Fibre-Reinforced Polymer laminate, with an arbitrary lay-up composition, based on existing knowledge and experiments, including the damage development under multi-axial stress states and stress redistribution. The research is limited to in-plane behavior, under tensile and compressive stresses. The static material response is characterized on a unidirectional ply level based on principal directions and based on experimental results obtained from the OptiDat program. The response predicted by the PFA for both tension and compression was in reasonable agreement with the experimental results. However, depending on the failure theory and degradation model used, there is potential for optimistic predictions of the laminate stress capacity. For future work, it is recommended to continue the research on a larger variety of laminate lay-ups and include more failure theories and degradation models.

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.

The increase in road traffic intensity and loading capacity of a truck over the last decades causes fatigue problems in existing bridges built in the 1960s and 1970s. For steel bridges, this means that the deck structure does not meet the current demands. A solution would be to replace these existing deck structures with Glas Fibre-Reinforced Polymer (GFRP) sandwich webcore deck panels. However, the ministry of infrastructure in the Netherlands has voiced its concern about the fatigue performance and displacements of these deck panels under the high traffic load and intensity. Furthermore, the knowledge about the fatigue performance of GFRP deck panels, applied in the main road network, is still limited. At the time of writing this report, the technical committee, CEN/TC 250 (responsible for developing structural eurocodes), establishes a technical design specification for Fibre-Reinforced Polymer (FRP) structures. This technical specification requires full-scale fatigue testing due to the complex failure modes that can occur. General fatigue damage summation methods like Palmgren-
Miner [30, 41] are not allowed by this technical specification. This report discusses the development of Virtual Fatigue Stiffness Simulation (ViFaSS), a numerical non-linear fatigue stiffness reduction model that can predict the fatigue performance of in-plane stress dominated Glass Fibre-Reinforced Polymer components, with a wide range of lay-up compositions, based on existing knowledge and experiments, including the damage development under multi-axial stress states and stress redistribution. The damage development includes damage accumulation dependency on damage history and damage development dependency on the load type, e.g. Tension-Tension (T-T) or Compression-Compression (C-C). With the low utilisation of the material strength in civil engineering applications, the research is limited to the stiffness degradation of the material. The numerical model is coupled with the Finite Element (FE) software SOFiSTiK where the component is modelled with shell finite elements. The fatigue material response is characterised on a unidirectional ply level based on principal ply directions and based on experimental results from the Optidat program [36]. The coupon response predicted by ViFaSS for constant amplitude T-T and bending fatigue loading was in reasonable agreement with experimental results. For future work it is recommended to extended the model with the ability to use non-linear material behaviour and to include the strength degradation caused by fatigue.

Ageing of infrastructure leads to an increasing demand for new technologies and design solutions in current bridge engineering. Over the last decades the traffic intensity has grown tremendously, while design codes and regulations have become stricter. Many current steel bridges realised in The Netherlands suffer from fatigue problems. Replacement of the bridges can be expensive, and thus engineers are asked to provide design solutions that can extend the lifetime of these structures. Rehabilitation through the replacement of steel orthotropic decks with Glass Fiber-Reinforced Polymer (GFRP) sandwich deck panels is considered as one of the few possible solution strategies. FRP's are considered a viable option, due to their versatility, high strength-to-weight ratio, fast installation possibilities, low maintenance costs and their resistance against both corrosion and fatigue. The increasing amount of bridges containing FRP structural elements demonstrates the high potential of the material. However, many engineering consultancies address to face difficult challenges when working with FRP. The main concern in the construction and design field is about the long-term performance of the material. Due to the viscoelastic nature of the polymeric matrix, FRP structural elements show complex creep and recovery behaviour under variable traffic loading. Current standards account for this traffic load by conservatively assuming that 40% of this traffic load should be accounted for in creep calculations, which originates from experience with concrete bridges. However, due to the fast recovery behaviour of FRP compared to concrete, this value might be too conservative. Based on current knowledge and experimental results, a numerical model was created that is able to predict the long-term creep deformation including both creep and recovery behaviour. The model uses experimental results based on UD-plies, which enables the model to calculate the long-term deformation of laminates with a wide variety of layups. The Finite Element Analysis (FEA) software package Abaqus has been used to model a FRP sandwich deck panel and calculate the time-dependent response under traffic loading. Finally, a FRP sandwich deck panel has been analysed by both the numerical model and according to the procedure prescribed by current standards. Results have shown that the amount of traffic load that is currently considered as permanent static load for creep calculations could be reduced. However, it is recommended for future research to improve the numerical model by using more accurate creep prediction models supported with profound experimental work. It is expected that this would lead to an even higher reduction of the amount of traffic load that is currently considered in design recommendations.