Resistance of prestressed hollow core slabs against web shear failure

Eurocode 2 presents a design method for the shear resistance, which according to harmonized standard EN 1168 is to be used for the web shear failure of prestressed hollow core slabs. To check the validity of the method, 49 shear tests on hollow core slabs with thickness 200-500 mm have been analysed. The Eurocode 2 method overestimated the mean shear resistance of all tested slab types. For 200 mm slabs and slabs with flat webs the overestimation was tens of percent. When the characteristic values of experimental and theoretical resistance were compared, the fit was better but there was still a considerable overestimation for 200 mm slabs and for the slabs with flat webs. On the other hand, the Eurocode 2 method was (over)conservative for 265 mm and 320 mm slabs with circular voids. The Eurocode 2 method ignores the shear stresses due to the transfer of the prestressing force. When these stresses were taken into account applying Yang's method, the accuracy for 265 mm and 320 mm slabs with circular voids was the same as when using the Eurocode 2 method but much better for the other slabs. Based on the results of the comparison, Yang's method for design against web shear failure should replace the present method in Eurocode 2. It is not acceptable, however, to adopt a design method which overestimates the characteristic resistance of some product type by 10% as Yang's method seems to do. Whether this is really the case, is still an open question because the number of tests on the problematic slabs was small. Furthermore, due to the nature of the type approval tests, some test specimens may have been weaker than the slabs typical of normal production. The Eurocode 2 method should not be used for slabs with flat webs without a reduction factor, and its applicability to other slab types should always be verified either numerically of experimentally before it is used.