Experiment on restrained steel beams subjected to heating and cooling

This paper describes the performance of restrained steel beams in fire experiments that were completed recently in the Fire Laboratory of Tongji University. It is shown that restrained steel beams have better fire-resistant capability than isolated steel beams. At the beginning of heating due to fire, an internal axial compression force was produced in the restrained beams by thermal expansion. When the temperature was up to a certain value, the internal axial compression force in the beams began to decrease, and eventually the compression force vanished and the tension force was initiated, due to the increase in the deflection of the beams causing a catenary action. This phenomenon explains why a restrained steel beam has higher fire-resistant capacity than an isolated steel beam. After the fire went out, a larger tension force was produced in the restrained steel beams by contraction as the temperature decreased. In addition, local buckling at the bottom flange of the beams near the ends was observed in the experiments. According to the results from the experiments, the stiffness of the axial restraint plays an important role in the behavior of restrained steel beams subjected to heating and cooling in a fire.