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On the Redistribution of Bending Moments in Two-Span RC Beams and Slabs Exposed to Fire



Author(s)

Robert Kowalski and Marek Urbański

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DOI:10.17265/1934-7359/2013.02.006

Faculty of Civil Engineering, Warsaw University of Technology, Warsaw 00-637, Poland

This paper shows consideration of decrease in cross-section stiffness in commonly used in practice RC (reinforced concrete) beams and slabs in cases when only reinforcing bars or only concrete compressed zone, which is subjected to fire. Analyses were based on: (1) standard fire curve [EN 1991-1-2]; (2) 500 ^oC isotherm method assumptions [EN1992-1-2]; (3) mechanical properties of reinforcing steel heated up to high temperature. Afterwards, based on estimated decrease of cross-sections stiffness, the redistribution of bending moments was calculated in some cases of two-span RC beams and slabs subjected to fire from their bottom face. Due to the bending moment redistribution, one could expect a reduction of bending moments in span cross-sections and an increase of support bending moment. As a result of this phenomenon, the ultimate limit state of the structural multi span elements might occur after shorter fire duration than it could be expected when redistribution of bending moments is neglected.

Concrete, cross-section, fire design, stiffness.