Development on ultimate strength equation of ferritic stainless steel (STS430) two-bolted connection

Abstract

This article presents the experimental and numerical results of cold-formed ferritic stainless steel (STS430) bolted connection with two bolts. Single-shear bolted connections with varying end distance were planned and tested. Block shear fracture and curling (out-of-plane deformation) were observed in specimens. Finite element analysis was performed to investigate the conditions for curling occurrence and the curling effect on the ultimate strength of ferritic stainless steel bolted connections with extended end distances and edge distances varying from 24 to 60 mm. Curling occurred for bolted connections with end distances exceeding 39 mm and edge distances exceeding 30 mm. Ultimate strength of curled specimens was reduced up to 33% compared to the ultimate strength of uncurled connection. Since current design equations do not consider the curling effect and the difference in material properties, they did not provide accurate ultimate strength predictions of specimens with typical block shear fracture and curling occurrence. Therefore, a modified block shear equation was suggested for ferritic stainless steel bolted connection with typical block shear fracture mode, considering the actual fracture path and shear stress factor. A revised equation was also proposed for specimens with strength reduction by curling influence, considering the concepts of bearing action against connected plate by bolt (bearing factor, C = 1.6) and net-section tensile fracture between two bolts perpendicular to the direction of the applied force. Moreover, additional experiments for six specimens were performed and the reliability of the two suggested equations in this study was verified.