Efficient hybrid strengthening for precast hollow core slabs at low and high shear span to depth ratios

Prestressed hollow core slabs are widely used in precast construction. The objective of this study is to understand the efficiency of hybrid strengthening technique at different levels of flexure to shear or shear span (a) to depth (d) ratios. Hybrid strengthening technique includes bonded overlay on the compression side and carbon fiber reinforced polymer (CFRP) composites on the tension side. Two different techniques are employed for the application of CFRP composites namely Near Surface Mounted (NSM) or Externally Bonded (EB). Fourteen full scale prestressed precast hollow core slabs were strengthened using different combinations of these techniques and tested at low (a/d = 3.75) and high (a/d = 7.50) shear span to depth ratio. The bonded overlay strengthening increased the peak strength by 59.2% and 89.0% respectively at low and high shear span to depth ratios. The externally bonded strengthening solely increased the peak strength by 16.9% and 87.6% at low and high a/d ratios, respectively. The NSM strengthening increased the peak strength by 49.4% and 68.9% at low and high a/d ratios respectively. Hybrid strengthening resulted in the best performance with highest increase in peak strength at both a/d ratios without a significant reduction in the ultimate displacement.