The durability of bridge connections is critical for the long-term performance of bridge systems with GFRP composite decks. This study investigates the shear fatigue behaviour of injected Steel Reinforced Resin (iSRR) connectors embedded in FRP composite decks, through a series of fatigue tests performed under different load ratios and exposure conditions. Twenty-four connectors are examined: twelve unaged reference specimens, eight specimens tested under varying R ratios, two connectors with deck parts submerged in water and two subjected to outdoor aging, both for a duration of one year. The results show that, despite the composite nature of the connector, the load ratio and mean load level have minimal influence on fatigue life. Instead, fatigue performance in the high-cycle regime is governed primarily by the applied load range. A unified F-N curve including all R ratios was developed, demonstrating the consistency of this trend and enabling fatigue-life prediction across different loading conditions. Environmental exposure led to measurable stiffness degradation but did not significantly alter fatigue life. These findings highlight the robustness of the iSRR connector and support its application in durable GFRP-steel hybrid bridge systems.

The design and effectiveness of fatigue load-dominated multi-membered tubular structures, such as offshore jackets, largely hinges on the fatigue performance of welded regions due to stress concentrations, necessitating the use of thick steel members. To address these challenges and reduce overall steel consumption, an innovative bonded joining technology known as wrapped composite joints demonstrating superior fatigue performance has been identified as a potential solution. Offshore conditions introduce combinations of different loading directions, resulting in complex stress states at the root of the composite wrap. This necessitates understanding the influence of such multi-axial loads on the static fracture resistance of the steel-composite wrapped joints. In this regard, interaction criterion exponents play a key role in understanding the correlation between different loading conditions. Ongoing research on wrapped composite joints focuses on these exponents, highlighting that delamination near the steel-composite interface stems as the main failure mechanism. In this context, this paper will develop a finite element (FE) model of X-shaped wrapped joint imposing fracture to the composite material and will study the superposition principle that exists between combined axial and bending loads. Combinations of load cases will be simulated to derive the interaction criterion exponents defining the failure envelope of such steel-composite wrapped joint. Modification to the current design recommendation is proposed with alternative an criterion with a good fit that aids in the design.

The durability and fatigue performance of bridge components are critical factors in their long-term viability. This study investigates the experimental results of fatigue tests on injected Steel Reinforced Resin (iSRR) connectors, a promising connection technology for Glass Fibre Polymer (GFRP) composite decks in bridge construction. This research expands on previous work by examining the impact of environmental exposure on the cyclic performance of iSRR connectors. A total of twelve iSRR connectors were subjected to fatigue testing. Two connectors were exposed to outdoor conditions for one year, two connectors were fully submerged in water, and four connectors served as reference specimens without aging. The experiments aimed to evaluate the fatigue resistance and performance degradation of the connectors under varying environmental conditions. Additionally, the cyclic loading was conducted with varying R-ratios to understand the influence of load ratio on the fatigue life of the connectors. The specimens were loaded until failure, and a detailed analysis of the failure modes was conducted to determine the impact of environmental exposure and the load ratio on the failure characteristics of the connectors. The findings provide insights into the effects of environmental exposure on the fatigue performance of iSRR connectors and contribute to the development of more durable and reliable connection technologies for GFRP composite decks.

Steel-Reinforced Resin (SRR) is a particulate material originally developed as an injectant for anchoring applications. More recently, it has been proposed as a filler material for cavities embedding mechanical connectors in FRP–steel hybrid bridges. In this context, the compressive behaviour of SRR becomes critical due to the multiaxial stress states and fatigue demands at a joint scale. This paper presents a comprehensive experimental and numerical investigation of SRR under monotonic, incremental cyclic, and fatigue compressive loading in unconfined conditions. A custom triaxial setup is also used to evaluate pressure sensitivity and strength enhancement due to confinement under monotonic loading. In parallel, micromechanical finite element models are developed to simulate the interactions between the resin matrix and the steel balls at the microscale, incorporating interface damage, friction, and cohesive failure. The models reproduce the observed nonlinear behaviour and reveal distinct Poisson's ratio responses in tension and compression, offering deeper insight into the mechanisms governing stiffness degradation, strain softening, and plateau behaviour.