Pure torsion tests on single hollow core slabs

Four tests on prestressed hollow core slab units were carried out. The slab units, two of them 200 mm and two 400 mm in thickness, were subjected to pure torsion. In all tests the observed failure mode was the same as the predicted one, i.e. cracking of top flange in angle of 45º with the longitudinal axis of the slab unit. Although the failure mode was abrupt, the slab units showed considerable ductility after the failure. None of them collapsed before the test had to be interrupted due to excessive rotation. For 400 mm slabs the torsional stiffness observed in the tests was close to that predicted by elementary calculation method, but for 200 mm slabs the predicted stiffness was 30% lower than that observed. The predicted torsional resistance was 60% and 70% of the observed resistance for 200 mm and 400 mm slabs, respectively, when the lower characteristic value for the tensile strength of the concrete was used for prediction.