Mechanical Properties of S700 Butt-Weld during and after Fire

Abstract

In this paper, experimental investigations are carried out to assess the weld strength of S700 steel during and after fire. Standard and nonstandard tensile coupons were tested during fire and postfire stages at temperatures ranging from 500°C to 800°C. In this experiment, all the standard specimens failed at the base material without any distinct yield plateau in the stress–strain relationship. The postfire specimens display yield strength reduction from ∼70% at 500°C to ∼55% at 800°C; while the ultimate strength reduced by ∼20%–30%. The slower cooling process (cooling in air) show lower ultimate strength regain than the quicker cooling process (cooling in water). The heat treatment does not affect the elastic modulus. As compared to the postfire residual ultimate strength of the parent material is not affected by heat treatment, the strength of air-cooled weld specimens display considerable (∼30% less) strength reduction. The S700 weld connection display lower strength as compared to most of the lower grade steel at elevated temperature. The ultimate strength of the S700 weld at elevated temperature display slightly lower strength than the Eurocode prediction. The weld material displays higher strength than the base material during and after fire.