BEHAVIOURS OF STEEL-CONCRETE COMPOSITE BEAMS AT LOW TEMPERATURES: MATERIALS AND STRUCTURES

This paper reported the low-temperature ultimate strength behaviours of steel-concrete composite beams (SCCBs) from material to structure levels. Firstly, low-temperature mechanical properties of constructional materials in SCCBs, e.g., concrete, headed studs, and mild steel plate for I-beams, were experimentally studied. The studies on constructional materials showed that decreasing the temperature (T) from 20 to-80 degrees C, the strength and ductility of headed studs and I- beam were generally increased; the decreasing Tincreased the strength, but reduced the ductility of concrete. Followed, the shear and tensile behaviours of headed studs in concrete at different Tlevels of 20 similar to-80 degrees C were experimentally investigated. Test results showed that decreasing T from 20 to-80 degrees C increased the shear and tensile resistance of headed studs, but showed different effects on ductility. Four-point bending tests on three SCCBs were performed at T of 20,-30 and -60 degrees C to investigate the low-temperature ultimate strength behaviours. These tests showed that at low temperatures all SCCBs failed in flexure with crushing of top concrete slab and yielding of bottom I-beam. Decreasing T from 20 to-30 and -60 degrees C increased the ultimate strength of SCCBs by 10% and 24%, respectively. A series of prediction equations were proposed to incorporate the effects of the decreasing T on compressive and tensile strength of concrete, shear and tensile capacity of studs, and ultimate bending resistance of SCCBs. Their accuracies have been validated by these material and member tests.