Numerical simulation of punching shear in RC slabs subjected to elevated temperatures

Abstract

Studies on the punching shear of reinforced concrete (RC) slabs exposed to fire are very limited. To address this shortcoming, a series of numerical analyses were carried out to study the effects of several parameters on punching shear behaviour of RC slabs under fire conditions. Variables of the study were: (i) gravity load levels before exposure to fire; (ii) presence or absence of shear reinforcement; (iii) duration of fire (at 30 min intervals), (iv) direction of fire (top and bottom face of slab); and (v) thermal conductivity limits. For this purpose, first, the shear response of a slab–column assembly failing in brittle punching shear under ambient temperature, chosen from the literature, was captured and, subsequently, sequential coupled thermomechanical analyses were carried out using the finite-element software ATENA. Results of the study show that the direction of fire significantly affects the deformation pattern and punching resistance of RC slabs; thermal conductivity plays a minimal role in this regard. Exposure to fire causes the reinforcements to yield at load levels well below the failure load. Finally, shear reinforcement has almost no effect on fire resistance of RC slabs. It is concluded that it is acceptable to ignore shear reinforcements in fire design of RC slabs.