Experimental and Numerical Studies on Efficiency of Hybrid Overlay and Near Surface Mounted FRP Strengthening of Pre-cracked Hollow Core Slabs

Prestressed precast hollow core slabs (PPHCS) are commonly used as floor elements in the precast buildings. These slabs could crack due to various reasons and can affect the overall integrity of the structure. Also, tension stiffening of concrete in PPHCS is not as effective due to the absence of additional reinforcement other than prestressing strands and the transition between a flexurally 'uncracked' and flexurally 'cracked' section is rapid. Therefore, strengthening of such cracked slabs is essential for ensuring its adequate performance. Effect of FRP strengthening of hollow core slabs is relatively well established. However, the effect of hybrid strengthening on the behavior of pre-cracked hollow core slabs is not fully understood yet. The performance of pre-cracked hollow core slabs strengthened with near surface mounting (NSM) of carbon fiber reinforced polymer (CFRP) laminates, and hybrid strengthening is investigated. Hybrid strengthening includes a combination of concrete bonded overlay in the compression zone and NSM CFRP laminates in the tension zone. A total of eight full-scale hollow core slabs are tested at two different shear span (a) to the depth (d) ratios of 3.75 and 7.50. Before strengthening of the hollow core slabs, the slabs were pre-cracked by applying the load equal to 65% of its ultimate capacity. Strengthening by NSM technique increased the ultimate capacity of the slabs by 50% whereas hybrid strengthening increased the strength by 130% when compared to pre-cracked control specimens. Finite element (FE) models were developed and calibrated to predict the behavior of tested hollow core slabs. Peak load predictions obtained from the finite element analysis had good correlation with the test results.