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

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 steel strands 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.