Performance of rectangular SRCFST stub columns under long-term loading and preload on steel tube

The performance of rectangular steel-reinforced concrete-filled steel tubular (SRCFST) stub columns throughout their whole life cycle should be studied since the steel tube bears initial stress during the construction stage and the full-section endures long-term axial loading during the service stage. A total of 7 SRCFST specimens were designed for a 1200-day sustained load test. Subsequently, axial compressive loading tests were conducted. The influence of the preload ratio (β) and the long-term sustained load ratio (n) on the initial strain values, creep behavior, failure modes, and load-deformation curves were studied. Besides, finite element simulations were conducted to analyze the internal force redistribution during the sustained load stage and the load-bearing behavior of various components in the load-bearing tests. The results indicated that considering the combined effects of different loading conditions influenced the failure modes and mechanical behavior of the specimens. When considering the combined effects of initial stress and long-term loading, the ultimate load-bearing capacity exhibited the most significant improvement, with a maximum increase of 13.4% compared with the long-term comparison specimens.