Wrapped composite joints arise as an innovative solution for joining circular non-welded hollow sections (CHS) in jacket support structures for offshore wind, intending to enhance fatigue performance and consequently reduce weight and costs when compared to traditional welded joints. Due to combined wave and wind loads, these joints are subjected to different multi-axial loading scenarios. Therefore, it becomes fundamental to establish an interaction criterion that accurately predicts the failure behavior provided by the superposition of different load conditions. Preliminary analyses have shown that, for instance, in cases where axial loads act simultaneously with bending moments, the joint resistance is underestimated when considering a linear summation of normalized strength values. Therefore, further studies are needed to determine the optimum interaction criterion exponents. In this context, this paper aims to present the results of an ongoing numerical investigation on the multi-axial load behavior of wrapped composite joints. Based on previous standards, a multi-axial loading interaction criterion is proposed, and a finite-element (FE) model is developed using the cohesive zone model approach. Distinct load cases are applied in a medium-scale X-shaped wrapped joint to evaluate the influence of the fracture toughness parameter on interaction failure criteria exponents. It was concluded that the given exponents do not seem to be affected by the change of interfacial strength and fracture toughness, which represents a valuable finding for the development of future design guidelines.

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.

This paper aims to propose a novel approach to assess the multi-crack behavior of layered fiber-polymer composites. The Compliance and R-curves generated from this novel approach were useful to understand the multiple delamination process, enabling to evaluate separately the strain energy release rate (SERR) related to each crack. A cohesive zone model was developed to simulate the failure process zone of three parallel cracks in web-flange junction (WFJ) specimens extracted from a pultruded bridge deck system subjected to transverse bending. The fracture parameters estimated based on the proposed approach led to a good agreement between the numerical model and the experiments in terms of load vs. displacement curves. Moreover, it was possible to observe that the formation of new cracks may lead to a significant drop on the R-curve, due to the closure of the former cracks.

Many recent works have shown that the capacity of pultruded glass fiber-polymer structural members is governed by interlaminar failure. However, there is still a lack of information regarding the fracture properties associated and the best techniques to be adopted. This paper aims to propose a testing methodology and to evaluate the interlaminar fracture of pultruded glass fiber-polymer specimens extracted from a composite bridge deck system. Both Modes I and II were investigated, through Double Cantilever Beam (DCB) and End-Loaded-Split (ELS) tests, respectively. The starter crack (or initial separation) was introduced via a water jet machine and the crack length was measured with the video extensometer technique. In all, nine different methods were applied to obtain the fracture toughness properties. The results are discussed and compared with 2D non-linear finite element models, where the cohesive zone model (CZM) approach was used. The Modified Beam Theory method (MBT_ASTM) presented the best results for crack propagation in Mode I, whereas differences lower than 1% from experiments were obtained when using the Corrected beam theory using effective crack length (CBTE) and the Experimental compliance method (EMC) methods for Mode II.

This paper aims to present an experimental investigation on the behavior of web-flange junctions (WFJs) rotational stiffness of pultruded fiber-reinforced polymer composites (FRP). Channels and I-sections were tested using a simple set-up, which was developed in order to experimentally characterize the junctions in a direct manner. The Digital Image Correlation (DIC) technique was used, allowing overall deflections and relative rotations between web and flange to be monitored. The WFJs' imperfections were analyzed through an optical microscope and correlated with the cracks' formation. Further, damage thresholds are identified using available stress equations for curved composite members and lower bound functions are proposed to simulate the junction stiffness retention. Finally, two Equations are developed in order to analytically predict pultruded junctions' rotational stiffness per unit of width. In general, the theoretical and experimental results agreed fairly well, with a maximum difference of 24% for I-sections and 38% for channels.

This paper aims to investigate the performance of pultruded glass fiber reinforced polymer (pGFRP)I-section columns subject to short-term concentric compression, bringing up a discussion on the relevant parameters affecting their local buckling behavior and the interpretation of tests results. An experimental program was carried out, including a detailed material characterization and twenty-nine compression tests on short I-columns made of either polyester or vinyl ester matrices, with variable flange width-to-section depth ratios (b_f/d), column lengths and local end conditions. The theoretical critical loads predicted using generalized beam theory (GBT)and finite element method (FEM)were compared to experimental results obtained by Southwell and Koiter techniques, with better agreements obtained for the latter. It is shown that, besides the length and local end conditions for loaded edges, post-buckling with associated non-linear elastic strains distribution throughout the cross-section and damage prior to buckling have relevant influence on the measured critical loads. On the other hand, the influence of the rotational stiffness of web-flange junctions were considered small for the material and cross-sections studied. Finally, results have shown that the usual boundary condition adopted in literature approaches a clamped condition instead of simply-supported one.