Mechanical behaviour of ultra-high strength concrete at elevated temperatures and fire resistance of ultra-high strength concrete filled steel tubes

• A new ultra-high strength concrete achieved 166 MPa.
• Compressive strength and elastic modulus decreased slower than normal/high strength concretes at elevated temperatures.
• Compressive strength and elastic modulus showed sharp reduction at 100 °C.
• Simple calculation method effectively predicted fire resistance of ultra-high strength concrete infilled tubes.

This paper introduces experimental study on mechanical behaviour of an ultra-high strength concrete (UHSC) at elevated temperatures and then a simple calculation method to predict the fire resistance of tubular column infilled with the UHSC. The cylinder compressive strength of the UHSC was 166 N/mm2 at room temperature. The compressive strength and modulus of elasticity of the UHSC were measured up to 800 °C. Then the temperature-dependent mechanical properties were compared with those of normal/high strength concretes provided in Eurocode 2 and ANSI/AISC 360-10, and with those of concretes in literature. The comparisons showed that the compressive strength and elastic modulus of the UHSC were generally reduced less than those of normal/high strength concretes at the elevated temperatures. The temperature-dependent mechanical properties were proposed for evaluating fire resistance of steel tubular columns infilled with the UHSC. The UHSC investigated in this project was shown to markedly improve the fire resistance in a number of cases well documented in the literature concerning tubular columns filled with the normal- and high-strength concretes.

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