预应力钢绞线高温力学性能试验研究

MECHANICAL PROPERTIES OF HIGH TENSILE STEEL CABLES AT ELEVATED TEMPERATURE

该文采用非接触式应变视频测量系统,开展了冷拉1860级钢绞线高温力学性能试验研究。基于试验测试的钢绞线高温应力-应变全过程曲线,建议了预应力钢结构用钢绞线的比例极限、弹性模量、名义屈服强度、断裂强度的高温折减系数以及高温应力-应变函数关系。试验结果表明,高强冷拉钢绞线高温下应力-应变全过程具有显著的应力强化阶段和颈缩阶段,1.25%应变下的高温名义屈服强度适用于高强冷拉钢绞线,钢绞线在高温下的捻度松弛效应对其高温力学性能存在影响。该研究成果进一步完善了预应力张拉钢结构用冷拉高强钢绞线高温下基本力学性能指标体系。

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.