Flexural and Shear Strength of Prestressed Precast Hollow-Core Slabs

Prestressed, precast hollow-core slabs are used extensively for floor and roofing systems in precast concrete construction in Saudi Arabia. Design of these precast structural units is based on ultimate load-carrying capacity of these members. Full-scale load tests were conducted on prestressed precast hollow-core slabs with different shear span to depth (a/d) ratio, which were loaded to failure to ascertain the ultimate load-carrying capacity of these slabs. A total of 15 slab specimens, 5 and 2.5 m in span and having three different depths, 200, 250 and 300 mm were tested to failure using four-point load test. It was interesting to note that the failure mode of hollow-core slabs changed from pure flexure mode to flexure-shear mode for slabs with depth greater than 200 mm. The web shear cracking strength of PPHC slabs decreased with an increase in depth of the slab. A transition from flexure-shear to web shear failure as a function of a/d was noted in the load tests. The analysis of the experimental results showed that the existing ACI code equations underestimated the flexure-shear strength of these hollow-core slabs. Based on regression analysis of experimental data, a modification is proposed in the existing ACI code equation which can capture accurately the mode of failure and ultimate load-carrying capacity of these slabs.