Web Shear Resistance of Prestressed Precast Deep Hollow Core Slabs

Prestressed, precast concrete hollow-core slabs (HCS) are plant-fabricated members with prestressing strands serving as the primary reinforcement. Shear resistance of such slabs is provided by concrete only because TICS units have no shear reinforcement. Recent studies indicated unconservative predictions for the web shear strength of deep HCS (thickness > 315 mm [12.4 in.]) using the ACI 318-05 equation. This paper investigates web shear capacity of a total of 24 HCS having depths ranging from 200 to 500 mm (7.87 to 19.68 in.). All slabs were manufactured using the dry-cast (extrusion) method and were provided by three different suppliers. The comparison of ACI 318-05 predictions with the obtained web shear strength of the tested slabs showed conservative predictions for shallower slabs, with the level of conservatism decreasing with the increase of slab depth. Moreover; the predictions were unconservative for deeper slabs with thicknesses of 470 and 500 mm (18.5 and 19.68 in.). On the other hand, ACI 318-14 web shear design provisions for HCS yielded very conservative predictions for the test deep slabs. Analysis of web shear strength of the tested slabs was carried out against possible causes of the unconservative ACI 318-05 predictions associated to deeper HCS. Based on that analysis, a modification to the ACI 318-05 web shear design equation was proposed and verged using the test data.