Tests of continuous post-tensioned concrete slabs under localised fires

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Modern concrete buildings increasingly rely on post-tensioned (PT) concrete for flat plate flooring (slab) systems. Post-tensioned concrete uses high strength prestressing steel (PS) tendons which, when tensioned after casting, pre-compress the concrete slab and result in excellent control of in-service structural deflections. However there are a number of load carrying mechanisms and failure modes that may be important for PT concrete structures in fire which have not yet been identified or adequately considered in the available literature. PS tendon continuity (particularly when unbonded) and thermal restraint can be expected to play significant roles in real PT structures. Because PS tendons can be unbonded and run continuously across multiple bays, tests on isolated, simply-supported members with short tendon lengths cannot be considered as representative. This paper presents the results of novel heated tests on three one way three span continuous and restrained monostrand PT concrete slabs (two of unbonded construction and one bonded). The slabs were tested under localised heating in their central span. Slabs were built with a realistic span to depth ratio as would be encountered in real construction. The slabs were rigidly supported on four steel columns of representative stiffness for a PT building; the result was three spans on four effectively fixed connections. The supporting columns were instrumented with strain gauges, making it possible to monitor the restraint forces generated during exposure to high temperature. Sustained loading was applied during testing using lead weights, and heating was applied using four radiant panels placed beneath the slabs. Thermocouples were placed at various locations throughout the slabs to provide thermal data, and a thermal imaging camera was used to generate heating profiles over the slab's soffit during testing. The slabs were monitored during both heating and cooling. The thermal and structural responses of these novel slabs during heating is presented and discussed.
Original languageEnglish
Title of host publicationInterflam 2013: 13th International Conference and Exhibition on Fire Science and Engineering.
PublisherInterscience Communications Ltd
Pages1131-1142
ISBN (Print)978-0-9556548-9-3
Publication statusPublished - Jul 2013

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