CFST Rib with Circumferential Gap and SWS Composite Defects

Most large-diameter concrete-filled steel tube (CFST) arch bridges adopt spiral-welded steel tubes for technical and economic reasons. However, during the steel tube manufacturing process, the welding temperature and other factors lead to a decreased spiral-welded seam (SWS) strength, initially. Furthermore, harsh environments, especially in the cold regions of northern China, during service and concrete dry shrinkage cause the steel tube and core concrete circumferential gaps to constitute composite defects in CFST structures. This paper presents a group finite element model analysis of the bearing capacity of a serviced CFST arch bridge rib with a circumferential gap and decreased SWS strength under small eccentric axial compression, using ultrasonic scanning field experience. The nonlinear behavior of the constituent and the effect of composite defects on the CFST behavior are investigated. Parametric studies are conducted to investigate the influence of the composite defects on the bearing capacity of the rib. Finally, a new ultimate strength index of the rib is proposed for the composite defects, and a simplified formula is presented to estimate the effects of the circumferential gaps and SWS strength decrease on the ultimate strength of the CFST arch bridge rib.