Shear Capacity of Composite Precast Prestressed HollowCore Slabs

No practically viable method yet exists to provide minimum shear reinforcements into pretensioned precast hollow-core slab (PHCS) units produced through an automated extrusion method. Subsequently, the web-shear strength of PHCS units with untapped depths greater than 315 mm (12.5 in.) should be reduced in half, according to current ACI 318 shear design provisions. Meanwhile, continuous precast floor construction has been commonly adopted in current practices by using cast-in-place (CIP) topping and/or core-filling concrete. However, shear test results on continuous composite PHCS members subjected to combined shear and negative bending moment are very limited in literature. To this end, this study conducts shear tests of thick composite PHCS members with untapped depths greater than 315 mm (12.5 in.) and various span-depth ratios subjected to negative bending moments, where noncomposite and composite PHCS units subjected to shear combined with positive bending were also tested for comparison purposes. Test results show that flexure-shear strength can dominate the failure mode of continuous PHCS members rather than the web-shear failure, depending on the presence of CIP topping concrete and shear span-depth ratio. In addition, it was also confirmed that the shear strength of composite PHCS members is marginally improved by using a core-filling method under negative bending moment at continuous support, and thus its shear contribution seems not fully code-compliant and satisfactory to that estimated using ACI 318 shear design equations.