Shear tests performed on precast, prestressed concrete hollow-core units with depths greater than 12 in. (300 mm) have shown that these units fail in the web-shear tension mode at forces smaller than those predicted by the Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (ACI 318 R-05). Some fail at shear forces equal to 60% of the ACI 318-05 predicted strength. This paper describes an experimental study that was conducted to investigate the prediction of the web-shear capacities of thick hollow-core units and to quantify the reasons why these thicker units are failing at lower shear forces than those predicted using the ACI 318-05 provisions. The findings suggest that the reduced shear capacity appears to correlate with increased end slip of the strand and with poorer consolidation of the concrete. The web-based shear equation in 318-05 was relatively ineffective in consistently predicting the shear capacities of deep hollow-core units. Fiber reinforcement of concrete mixtures could enhance web-shear strength since the fibers would greatly increase tensile strength of the concrete.
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Palmer et al. (2011) studied this question.
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