Fire tests on unbonded post-tensioned one-way concrete slabs

This paper presents the results from four fire tests carried out on one-way spanning unbonded post-tensioned concrete floor slabs. The elevated temperature tests are augmented with the results from two additional tests carried out to failure, on slabs with identical geometry and tendon reinforcement, at ambient temperature. The fire tests highlighted the different structural response between using limestone and Thames gravel aggregates and different restraint conditions to longitudinal thermal expansion. It is shown that slabs with Thames gravel aggregates have a much higher deflection compared to slabs with limestone aggregates. The restrained slabs had lower vertical deflection compared to the equivalent unrestrained slabs. In all the fire tests, cracks directly inline and parallel to the tendons occurred owing to thermal stresses at relatively low tendon temperatures, which were not observed in the ambient tests. In one fire test, which was taken to overall collapse, it was shown that the strength reduction factors for tendon reinforcement currently used in the European design codes is conservative. The test data, comprising tendon strains, vertical and horizontal displacements and temperatures through the slab, will allow validation of developed computer models to predict the behaviour of unbonded slabs under fire conditions.