Behaviour of restrained steel beam with reduced beam section exposed to fire

Abstract

Reduced beam section (RBS) is one of the connection types, which is economical and popular for use in steel moment frames in seismic regions. By cutting some portions of the beam flanges near the column face, the RBS connections are designed to form plastic hinge within the RBS zone so that it could enhance the structural seismic performance. However, the steel beams with RBS connections have to provide robustness when exposed to fire. Although the responses of ordinary steel beams to elevated temperatures have been investigated over the last few decades, there has been very limited research on the behaviour of steel beams, with RBS connections in fire. This study includes a series of numerical analysis, to investigate the high-temperature performance of steel beams with RBS connections, compared to the responses of ordinary steel beams to fire. Various parameters have been considered, including the types of fire curves, the levels of beam-end restraints and the cutting profiles of the RBS connections. Overall, the deformation shape of RBS beams at high temperature is similar to that of ordinary steel beams, whereas the RBS beams could have longer period of fire resistance. The cut section actually provides both rotational and axial ductility/deformability to the connection, enhancing its fire resistance. Moreover, the cutting length, proposed by EC8, is also adequate for fire design. The minimum distance, between the RBS zone and the beam-end, proposed by FEMA-350 has been shown sufficient.