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

Abstract

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.

Modelling of unbonded post-tensioned concrete slabs under fire conditions

“…The main objective of this paper is to provide a better understanding for the behaviour of post-tensioned unbonded one-way spanning concrete slabs in fire conditions through numerical investigation. An efficient nonlinear 3-D finite element model was developed using ABAQUS [18] and verified against the tests conducted by Bailey and Ellobody [8]. A parametric study has been conducted to study the effects of the change in the aggregate type, load ratio and boundary conditions on the behaviour of unbonded post-tensioned one-way concrete slabs at elevated temperatures.…”

“…As shown in Table 1, six tests-two at ambient temperature [21] and four at elevated temperature [8]-were carried out on unbonded post-tensioned slabs. The slabs were designed according to BS 8110-1 [22] and the Concrete Society Technical Report 43 [23].…”

“…Further details of the tests and results obtained are given in Refs. [8] and [21] for the fire and ambient tests, respectively.…”

“…Recently, Bailey and Ellobody [8] conducted a series of tests on unbonded post-tensioned one-way concrete slabs in fire conditions. Four slabs were subjected to a fire under a static load equal to 50% of their capacity in the cold condition.…”

Finite Element Modeling of Post-Tensioned Two-Way Concrete Slabs under Flexural Loading

“…The behaviors of post-tensioned concrete elements were studied experimentally by Williams and Waldron [3], Yang et al [4], Ranzi et al [5], Bailey and Ellobody [6,7] and others. A collection of studies by several researchers explains the FE analysis of the behavior of reinforced concrete structures such as shear failure of slabs, cyclic loading of columns, and the behavior of structure to seismic and bond models between concrete and steel.…”