MECHANICAL PROPERTIES OF HIGH TENSILE STEEL CABLES AT ELEVATED TEMPERATURE

This study is motivated by increasingly prevalent use of cable-tensioned spatial steel structures and suspension bridges. Fire is one of the extreme conditions that need to be taken into consideration in the design of such structures. Steady-state tests have been conducted on steel cables with tensile strength of 1860MPa, which consist of a group of 7-wire twisted strands, to study their full range of stress strain relationships at elevated temperature. The thermal elongation test of steel cables has also been conducted. A charge-coupled device camera (CCDC) system is used to capture the full range of the stress-strain relationship of high tensile strength steel cables till rapture at elevated temperature. The reduction factors of proportional limit, elastic modules, effective yield strength and rupture strength at different temperature were obtained from the steady state tests and compared with that proposed by EN 1992-1-2. The test data discovered that EN 1992-1-2 overestimated effective strain up to 2% and ignored the stress hardening phase for high tensile strength cables within the full temperature range. The effective yield strength with 1.25% strain and a full range of stress-stain model considering stress hardening phase, which has been ignored by EN 1992-1-2, are proposed by the present test data. Finally, several sets of reduction factors and thermal elongation coefficients as a function of temperature have been proposed by fitting test results. The present test data discovered that the reduction factors of pre-stressing strands proposed by EN 1992-1-2 for pre-stressing concrete is not suitable for steel cables which always employed by tensile steel structures. The reduction factors proposed by present paper are reasonable for steel cables. Furthermore, the comparison of reduction factors between steel cables and single wires, it discovered the effect of twist on the mechanic properties at elevated temperature.