Punching shear behavior of strengthened and unstrengthened heat-damaged reinforced concrete flat slabs: Experimental and NLFEA study

The behavior of the brittle punching shear failure in two-way flat slabs was investigated in this study using experimental and nonlinear finite element analysis approaches. The reinforced concrete slabs were tested under the effect of strengthening carbon fiber reinforced polymer sheets (strengthened and un-strengthened), temperature value (23, 200, 400, and 600 oC), and the behavior was captured at the material and system levels. Generally, the punching shear performance was significantly worsened upon exposure to the heat-damage effect, where increasing the temperature value increases the resulting cracking intensity. In addition, strengthening the flat slabs improves the overall structural behavior where the ultimate loadcarrying capacities, cracking loads, and toughness values are increased. The detailed structural behavior, including the cracking propagation, failure modes, strain values, and displacement profiles at various high temperatures, were captured using the nonlinear finite element analysis. Generally, the resulting improvement is higher for specimens damaged at higher temperatures, with the load-deflection behavior flattening with increased deflection values. Moreover, toughness was improved significantly by strengthening with reduced failure brittleness. Finally, the stiffness-deflection curves at 400 oC and 600 oC specimens start with a flattened shape but experience a sudden drop in the strengthened ones, revealing that failure occurs compared to specimens at lower temperatures.