Experimental study on behavior of restrained high strength Q690 steel beams exposed to fire

In comparison to the isolated steel beam, the restrained steel beam is able to sustain fire loads using the effect of the surrounding restraints. However, Q690 steel has lower resistance to high temperatures than other types of carbon steel. To address this gap, a series of experimental tests on restrained high-strength Q690 steel beams subjected to fire are reported in this paper. Four full-scale restrained high-strength Q690 steel beams were investigated under several fire scenarios, and one was tested at room temperature. In this study, three transient tests and one steady-state test were chosen to fully comprehend the behavior of the restrained high-strength Q690 steel beams exposed to fire. Under the two test conditions, the impact of the steady-state and transient conditions on the fire response of the restrained Q690 steel beams are compared, and the variation of axial peak force, bearing capacity, and deflection were analyzed. The results showed that the critical temperature of the steady-state test is close to the critical temperature of the transient test, and the maximum axial force of the steady-state test is comparable to the one of the transient test. Due to the combined action of load and axial forces, the restrained Q690 steel beam generally develops flexural-torsional buckling failure after reaching the critical temperature in transient tests. In comparison, the steady-state test exhibits early flexural-torsional buckling behavior before reaching the critical temperature. In this study, three transient tests and one steady-state test were chosen to fully comprehend the behavior of the restrained high-strength Q690 steel beam in fire. Under the two test conditions, the impact of the steady-state and transient on the fire response of the restrained Q690 steel beams are compared, and the variation of axial force peak, bearing capacity, and deflection are analyzed. The results showed that the critical temperature of the steady-state test is close to the critical temperature of the transient test, and the maximum axial force of the steady-state test is comparable to the transient test. Due to the combined action of load and axial forces, the restrained Q690 steel beam generally develops flexural-torsional-buckling failure after reaching the critical temperature in transient tests. In comparison, the steady-state test exhibits early flexural-torsional-buckling behavior before reaching critical temperature. • A series of experimental tests on restrained high-strength Q690 steel beams subjected to fire are carried out. • The impact of the steady-state and transient on the fire response of the restrained Q690 steel beams was compared. • The effect of load on fire resistance and critical temperature of restrained Q690 steel beams was investigated.