Effects of thermal creep of prestressing steel on post-tensioned concrete slabs in and after fire

Abstract

The effects of thermal creep of prestressing steel on the structural responses and load-carrying capacities of post-tensioned (PT) concrete slabs in and after fire are investigated numerically based on the calibrated thermal creep model and parameters. The finite element (FE) models of the slabs are built up using solid elements by the package ABAQUS, taking into account the frictionless contact between unbonded presressing steel and surrounding concrete. The nonlinear material properties of concrete and prestressing steel during and after a period of elevated temperatures are incorporated in the FE models. The FE models developed are validated against available test results [1, 2] in respect of stresses of prestressing steel, slab deflections and failure loads at ambient condition and in fire. Failure analyses of PT concrete slabs are conducted to predict the fire endurance under standard fire condition (ISO 834) and the residual load-carrying capacities after various durations of fire. The material models of prestressing steel include the Eurocode model that implicitly takes thermal creep into account, and new models with and without thermal creep. The failure criteria adopted in the analyses are defined as concrete crushing, rupture of prestressing steel and their combination. The results obtained from the three models are compared and discussed. In particular, implications for fire-resistant design of PT concrete slab in fire and residual load-carrying capacity after fire are examined.