The role of CFRP strengthening in improving the punching shear behavior of heat-damaged flat slabs with openings of different sizes and locations

Abstract

The punching shear behavior of twenty simply supported RC flat slabs of mm3) dimensions was examined in this study where concentrated loading was applied using a 150 mm central square column. However, the effect of the following parameters was evaluated: (1) CFRP strengthening, (2) ambient and elevated temperatures (23 C, 200 C, 400 C, and 600 C), (3) opening existence (with or without), (4) opening location (directly at the column face or 60 mm a way), and (5) square opening side length (70 mm or 200 mm). Strengthening was done by four 75 mm wide CFRP strips applied at the bottom face of the slab to surround the column and opening region. It was found that the cracking intensity is directly affected by the exposure temperature with the cracking visibility at the opening internal sides. In addition, strengthening increases the slab’s stiffness by larger percentages for slabs with small openings compared to those with larger ones at ambient and normal temperatures with the differences being reduced at higher temperatures. Moreover, strengthening plays a major role in improving the slab’s deflection capacities by 10–90 % compared to the control specimen. Finally, the punching shear failure brittleness was significantly reduced by the CFRP-strengthening as the ductility of the strengthened specimens was increased as a result of the cracking intensity reduction.