Experimental and numerical investigations of fire resistance of continuous high strength steel reinforced concrete T-beams

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Abstract

This paper presents experimental and numerical results of performance and fire endurance of high strength steel reinforced concrete (RC) continuous T-beams under the standard ISO 834 condition. The fire tests included six specimens using steel reinforcement of 500MPa yield strength with different load levels and reinforcement ratios. In all cases, the failure mode was flexural failure due to the formation of a plastic hinge mechanism. However the sequence of plastic hinge appearance was different from that at ambient temperature due to the increased support bending moments in fire as a result of restrained thermal bowing. Formation of a plastic hinge mechanism indicates sufficient reinforcement ductility to enable complete redistribution of bending moments and absence of any buckling failure of the T-beam stem in the compression region at very high temperatures. The load ratio was the most critical design parameter, with the fire resistance times of the specimens being146min, 93min and 64min for load ratios of 0.3, 0.5 and 0.7 respectively. For the T-section, the temperature field of the flange plate was similar to that of a one-side fire exposed RC slab, and that of the web similar to that of a three-side fire exposed RC rectangular beam. Further numerical simulation results using steel reinforcement of 690MPa yield strength confirm that continuous, high strength steel reinforced concrete T-beams can be designed using plastic analysis.

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This paper presents experimental and numerical results of performance and fire endurance of high strength steel reinforced concrete (RC) continuous T-beams under the standard ISO 834 condition. The fire tests included six specimens using steel reinforcement of 500MPa yield strength with different load levels and reinforcement ratios. In all cases, the failure mode was flexural failure due to the formation of a plastic hinge mechanism. However the sequence of plastic hinge appearance was different from that at ambient temperature due to the increased support bending moments in fire as a result of restrained thermal bowing. Formation of a plastic hinge mechanism indicates sufficient reinforcement ductility to enable complete redistribution of bending moments and absence of any buckling failure of the T-beam stem in the compression region at very high temperatures. The load ratio was the most critical design parameter, with the fire resistance times of the specimens being146min, 93min and 64min for load ratios of 0.3, 0.5 and 0.7 respectively. For the T-section, the temperature field of the flange plate was similar to that of a one-side fire exposed RC slab, and that of the web similar to that of a three-side fire exposed RC rectangular beam. Further numerical simulation results using steel reinforcement of 690MPa yield strength confirm that continuous, high strength steel reinforced concrete T-beams can be designed using plastic analysis.

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