Parametric Study on Ultimate Strength of Four-bolted Connections with Cold-formed Carbon Steel

The curling(out-of-plane deformation in the plate thickness direction) influence on the ultimate strength of cold-formed stainless steel bolted connection has been investigated and modified equations for predicting the ultimate strength considering strength reduction caused by curling through finite element analysis have been suggested by previous researchers. In this paper, single shear four-bolted connections fabricated with thin-walled carbon steel commonly utilized in the light-weight structural members of building were tested under static shear in order to investigate block shear fracture behavior and curling influence on the ultimate strength and fracture mode. Main variables of specimens are plate thickness and end distance parallel to the direction of loading. Curling in the perpendicular direction of applied force also occurred for bolted connections with a relatively long end distance and thin plate. The curling occurrence caused a sudden strength drop and reduced the ultimate strength of bolted connections. Current design specifications such as AISC, AIJ and AISI for block shear strength were summarized and it is known that design equations did not provide the accurate prediction of ultimate strength and fracture mode for thin-walled carbon steel bolted connections. Strength reduction by curling and the condition of curling occurrence were investigated through an additional parametric finite element analysis. As a result, revised strength equations for block shear fracture and bearing fracture were suggested considering fracture path and curling effect and their validity was also verified.