Experimental study on S700 T-stub in heating and cooling during fire

Abstract

In this paper, experimental investigations were carried out to assess the strength of S700 steel material and T-stub made from S700 steel in heating and cooling during fire with an emphasis on cooling stage fire (decreasing temperature). T-stub is a simple idealization of tension zone in bolted connection as T-shaped joint. In total, 17 coupons were tested in room temperature, growth (growing/ increasing temperature), cooling and postfire phases. It was observed from the tensile test data, that the growth phase properties were not similar as the cooling phase properties, however, about 90% of strength regained at the end of cooling phase, (i.e., in postfire specimens). 22 T-stubs of two geometric configurations were tested for axial capacity in heating and cooling during fire. In both the geometric configuration, the mode of failure at room temperature changed to other modes at elevated temperatures. The mode of failure at elevated temperature depended on the relative strength of T-stub and the bolts. The experimental results were compared with existing codal provisions – Eurocode 3 and AISC 360. It was found that the Eurocode prediction was close to the experimental results, while AISC prediction was highly conservative, which might be attributed to the non-consideration of bolt strength (proportionate reduction in strength due to fire) directly during the strength prediction.