Post-fire block shear strength of thin-walled carbon steel bolted connections

Abstract

Steel structures that survive a fire can be restored afterwards, but it is necessary to ensure that they have sufficient strength and stability to serve for the rest of the projected life. This paper is concerned with the post-fire behaviour of thin-walled carbon steel bolted connections, which has received limited attention to date from the research community. The experimental programme of this study includes testing thirty-four specimens of bolted connections and thirty-four coupons. The specimens and coupons were exposed to heating of 400 °C or 700 °C for a specified time (30 min, 60 min, 90 min, and 120 min), and cooled either by air or water. The results presented that some physical changes occur after the steel was exposed to high temperatures and it was mainly a reduction in the thickness. The yield stress and the modulus of elasticity of the heated coupons were affected mainly by the heating temperature and time, and an insignificant effect was recorded on the method of cooling (the maximum difference was 4%). The strength of the post-heated bolted connections was improved significantly in air-cooled specimens and reduced clearly in water-cooled specimens. The opposite behaviour was noticed for the connection ductility. The failure modes of the coupons and the bolted connections were not influenced by the heating temperature and cooling method. The coupons failure was a typical tensile fracture and the bolted connections failure was block shear with curling. The post-fire mechanical properties were used successfully to predict the post-fire strength of the connection.