Collapse behavior investigation of simple connections for uninsulated composite beams under fires

Detailed FEM analysis models were created for steel floor structures including uninsulated beams and slabs. The simulated collapse behavior at elevated temperatures under fires involved the rupture of slab reinforcement around the bolted simple connections of the uninsulated secondary beams. Corresponding to the numerical results, full-scale heating and loading experiments were conducted. The vertical and horizontal loads were applied simulating the behavior of the connection of an uninsulated secondary beam at elevated temperatures. The experiment revealed that the critical collapse behavior around the connection is rupture of slab reinforcement followed by shear failure of the bolts. In the case that slab reinforcement is wire-mesh, the reinforcement may rupture under the out-of-plane flexural deformation during the development process of tension mechanisms associated with large deflection. In the case that deformed reinforcement is used for the slab, deformation capacity against out-of-plane deformation of the slab significantly increased. The collapse load under the tension mechanism was approximately 1.5 times the weight of a standard office floor, even with nearly minimum reinforcement for practical slab design.