Fire resilience of composite beams with simple connections: Parametric studies and design

Simple (shear) connections are designed to resist vertical shear forces resulting from gravity loading. During a fire event, floor systems expand and rotate, imposing axial forces (compressive and tensile) on simple connections. This paper presents the results of analytical parametric studies conducted to expand the experimental database and evaluate the structural response of composite beams with simple connections subjected to combined gravity loads and design fire scenarios. The parametric studies were conducted using 3D finite element models of partial frame assemblies consisting of composite beams with simple connections. These models were developed and benchmarked previously by the authors [1] using experimental data [2, 3]. These models explicitly accounted for the effects of geometric and material nonlinearity including concrete cracking and crushing, steel yielding and fracture, and the interaction between various structural components. The parameters included in the analytical studies were the connection type (shear-tab, single-angle, double-angle), deck type (flat slab, perpendicular metal deck), composite slab continuity across multiple bays, slab reinforcement type (wire mesh, mild steel), fire resistance rating of the design, and the design fire scenario (1 hour fire with cooling, 2 hour fire with cooling, E119). The results from the parametric studies indicated that for typical composite beams and simple connections designed with certain (n-hour) fire resistance rating, and subjected to design fire scenario with the same (n-hour) heating followed by cooling, there was no premature fracture failure of the connection leading to collapse of the composite beams. The continuity of composite slab across bays and the steel reinforcement has a significant influence on the performance of the simple connections, and the resilience of the composite beam system.