1989

Pajari, Matti

A design method is proposed for hollow-core slabs with or without structural in-situ concrete topping. The failure mechanisms considered are flexural tensile failure, flexural compression failure, flexural cracking failure, anchorage failure, shear tension failure and failure at the interface of precast and in-situ concrete. Prediction of the cracking moment and deflections are also considered. A computer program, including the design method, was developed and used to simulate 348 full-scale loading tests. Comparing predicted cracking cpacities with those observed showed the flexural tensile strength of concrete to be independent of the slab thickness. At an assumed flexural tensile strength of 1.1 times the tensile strength (5 % fractile), roughly 80 % of the predicted cracking capacities were smaller than those observed. The prediction of shear capacity was very accurate for 265 mm slabs and fairly accurate for thinner slabs, but the tensile strength of concrete had to be reduced by 30 % in order to make the prediction for 400 m slabs conservative enough. No problems arose with the bending capacity, when the 0.2 % yield strength was used for the strands. In composite slabs, the observed deflections and cracking capacities agreed well with those predicted when the effective differential shrinkage was taken to be 35 % of the differential shrinkage calculated according to the CEB-FIP Model Code.