Fire resistance of steel-concrete cellular composite beams having different end restraints

To determine the fire resistance of steel-concrete cellular composite beams having different end restraints, constant-load heating tests and numerical simulation analyses were conducted on end-hinged and rigidly-jointed circular-holed cellular composite beams to investigate the cross-sectional temperature field, displacement changes, and damage patterns of honeycomb composite beams during the entire fire process. The results showed that there was local buckling of the end web and lower flange of the beam, and lateral instability of the lower flange, in both types of beam-end constrained cellular composite beams after the fire. The definition of the fire endurance limit of the beam-end constrained cellular composite beam is the deflection at the mid-span reaching 1/20 of the beam span. Under ISO-834 standard heating conditions, the hinge and rigid connection restrained composite beams reached their fire resistance limit at 90 min and 75 min, respectively. Due to the existence of welds, the overall torsional performance of fixed confined cellular composite beams was better under fire. After a fire, the rigid connection restrained composite beams had more complex crack distributions on the concrete surface. During heating up, the opening edge temperature of the steel beam web was higher than that of inter hole web. The recovery ratio of deformation after a fire for the hinge and rigid connection restrained composite beams was 10.6% and 7.5%, respectively. The numerical simulation results were in good agreement with the experimental results, thus verifying the correctness and validity of the finite-element model.