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The girth welds of the steel connections in subsea pipelines are subjected to combined fatigue loading and static tensile loading in most of their service life. In this paper, both experimental and numerical studies are presented on the fatigue behavior of Carbon Fiber Reinforced Polymer (CFRP) composites repaired steel connections under combined loads. In the experimental program, each specimen is designed to be formed by two steel plates joined together by single-sided girth welds as a simplification of subsea pipelines, and reinforced by CFRP sheets on one side. The applied loads include a constant amplitude tensile cyclic load combined with a tensile static load, which is perpendicular to the cyclic load. The experimental results reveal that the superimposition of the tensile static load leads to a prolonged fatigue life. The effect gets more noticeable with increased tensile load. To further this study, an analytical model is developed on the basis of the Linear Elastic Fracture Mechanics (LEFM) method. It can be used to predict the fatigue lives efficiently. The comparisons with experimental results reveal that the analytical method is able to reasonably predict the fatigue crack growth life. Parametric studies are therefore performed using the proposed analytical model. The influence of CFRP layers, stress range and tensile static stress on the fatigue life was evaluated.

Welded connections are extensively used by the precast concrete industry to ease construction. When the seismic resistance and ductility of a building incorporating precast concrete elements needs to be assured, the connections should be carefully designed and constructed to avoid undesirable structural performance. This paper discusses aspects related to an analytical and experimental programme conducted to investigate the response of a connection detail for coupling precast concrete walls in low to medium rise buildings. The connection consists of a rectangular steel plate with a concentric circular perforation. In this way, a weak but ductile link is introduced in the system. Using the principles of capacity design, the walls can be designed as if coupled and with energy dissipation taking place in the connection. Simplified expressions are presented to evaluate the shear stiffness and the yield and ultimate strength of the perforated steel plates, based on theory and the experimental data collected during the test.