预应力钢绞线温度膨胀及高温蠕变性能试验研究

EXPERIMENTAL STUDY ON THERMAL EXPANSION AND CREEP PROPERTIES OF PRE-STRESSED STEEL STRANDS AT ELEATED TEMPERATURE

火灾高温下钢绞线的温度膨胀及高温蠕变性能是影响张拉钢结构抗火能力的重要因素。该文以1860级预应力钢绞线为研究对象,采用非接触式应变视频测量系统,测试了钢绞线在15个温度水平下的热膨胀应变,得到热膨胀应变随温度的变化规律,并拟合出热膨胀系数计算公式。研究发现,大约750℃时钢绞线材料发生相变,导致热膨胀应变突变。通过钢绞线在不同温度及应力水平下的高温蠕变试验,得到蠕变应变与时间的关系曲线,并建议了钢绞线高温蠕变计算公式。高温蠕变试验现象表明,在较高温度及应力水平时,蠕变会导致钢绞线断裂;对经2 h高温蠕变未断裂的钢绞线自然冷却到常温后,进行抗拉强度试验,发现其抗拉强度有一定程度的退化,且经历的蠕变温度越高,应力水平对高温蠕变后试件抗拉强度的退化影响越明显。

Thermal expansion and thermal creep of pre-stressed steel strands strongly influence the fire resistance of tensile structures in fire. In this paper, the thermal expansion and thermal creep tests have been conducted by non-contact video gauge for pre-stressed steel strands with tension strength of 1860 MPa at 15 temperature points. The formula of thermal expansion dependent on temperature history has been developed by fitting to the thermal stress courses resulted from tests at elevated temperature. It reveals that the thermal expansion drops sharply due to the phase change of material at 750℃ or so. The thermal creep tests under different temperatures and stress ratios are conducted to obtain the relationship between thermal creep stress and fire course. The formula of thermal creep of pre-stressed steel strands dependent on fire course has then been developed. The tests results show that the thermal effect can cause pre-stressed strands to break at higher stress level and higher temperature. The tensile strength tests have been also conducted after the pre-stressed steelstrands cooling down to ambient temperature. The tests results show that the tensile strength of pre-stressed steel strands partly decreases. With the higher temperature at which thermal creep tests experienced, the decrease of the tensile strength of pre-stressed steel strands depends more on stress ratio at ambient temperature.