BENDING STRENGTH OF BEAM JOINTS FASTENED BY HIGH STRENGTH BOLTS AT ELEVATED TEMPERATURES

Abstract

Full scale fire resistance experiments of protected steel beams with joints were conducted to investigate collapse modes and bending strength of the beam joints at elevated temperatures. Each of the five beam specimens has a joint at the middle, which is fastened by high strength bolts. A concentrated vertical load is applied so that the central zone of the beam including the joint is subject to a uniform bending moment. The beams are heated in a furnace by the ISO834 standard fire temperature curve after the stabilization of the applied loads. In each experiment, the beam collapsed in either of the two collapse modes; a bending collapse of the beam due to shear failures of high strength bolts, and a bending collapse of the beam itself. In particular, for the case of the beam joint designed to have the full strength connection, the collapse mode changed from the latter to the former with increasing ultimate temperature. It was found that the bending strength of the beam joints can be estimated by a theoretical formula based on the simple plastic theory.