Experimental investigation of the post-fire response of single-shear bolted lap joints

Purpose This study aims at investigating experimentally the behavior of single-shear bolted lap joints with N-bolts and X-bolts (XB) after exposure to fire temperatures. Design/methodology/approach Sixteen single-bolted lap joints with M20 Grade 8.8 bolt are heated to various targeted temperatures ranging from 400 °C to 900 °C and subsequently cooled back to ambient temperature. Following the heating and cooling stages, the specimens are subjected to direct tension tests to determine the reduction in shear capacity and slip resistance of the lap joints. Post-fire reduction factors are estimated from the axial load–displacement curves to determine the residual strength of N-bolted and X-bolted lap joints after exposure to fire temperatures. These reduction factors are incorporated into Equation J3-1 of ANSI/AISC 360 (2022) for the design of simple bolted connections acting in shear after fire exposure. Findings The results show that X-bolted lap joints exhibit a larger reduction in bolt shear capacities compared to those with N-bolts. The shear strength of lap joints with N-bolts begins to degrade after exposure to 500 °C, reaching a maximum reduction in shear strength of 40% at 900 °C. Conversely, the strength of lap joints with XB starts to degrade after exposure to temperatures beyond 400 °C, reaching a maximum reduction in shear strength of 42% at 750 °C. The post-fire reduction factors computed in this study showed that XB reduction factors are more conservative than the N-bolts and those available in the literature. Practical implications This study provides preliminary data for the development of design guidelines of bolted connections with N-bolts and XB after fire exposure. Originality/value This study provides preliminary data for the development of design guidelines of bolted connections with N-bolts and XB after fire exposure.