拉脱法检测技术-时间及温度效应修正

预应力钢绞线张拉完成后,有效预应力会受时间及温度的影响而发生变化.为了准确揭示锚下有效预应力在温度和时间影响下的变化规律,提高拉脱法检测技术在实际工程中的测试精度,进行了时间效应和温度效应的试验研究.当钢绞线张拉时,在锚下放置压力传感器(可同步采集温度数据),对不同跨度、不同截面形式预制梁中的钢绞线进行锚下有效预应力及温度的实时动态监测.其中长期试验(1个月)40束,短期试验(72 h)27束,分别用于分析温度及时间效应对于锚下有效预应力变化的影响,并对大量的测试数据进行数理统计分析.研究结果表明:500 h前,锚下预应力存在整体的衰减趋势,且出现类似正弦波的变化,该变化由温度变化导致,相比时间效应,温度对锚下有效预应力的影响较小;500 h后,预应力的衰减趋势减小,处于相对平稳状态;48 h内,不考虑温度影响,67根钢绞线的衰减规律存在一定离散性,且离散性随时间的增长而增大;每组钢绞线预应力残余率在48 h内均服从威布尔分布.研究得到的锚下有效预应力温度和时间效应修正公式可对实际桥梁工程检测中拉脱法的测试结果进行温度和时间修正.

Correction of Time and Temperature Effects for Lift-off Test Technology

After a prestressed steel strand is tensioned, the effective prestress changes in accordance with time and temperature. To reveal accurately the variation law of effective prestress under anchors based on the influence of temperature and time, and to improve the test accuracy of lift-off test technology in practical engineering, an experimental study of time effect and temperature effects was conducted. When the steel strand was tensioned, a pressure sensor was placed under the anchor to perform real-time dynamic monitoring of the effective prestress and temperature of the steel strand in the precast beam with different spans and sections. Tests of 40 and 27 bundles in the long-term (1 month) and short-term (72 h), respectively, were used to analyze the effects of the temperature and time effects on the effective prestress changes under the anchor. Statistical analyses of several test results were performed. The results show that in the previous 500 h, an overall damping trend of the prestress occurs, and a similar sine wave change occurs during the entire test process. A similar sinusoidal wave change is caused by the temperature change. Compared with time effect, the effect of temperature on the effective prestress under anchors is less. After 500 h, the damping of the effective prestress decreases and the effective prestress is in a relatively stable state. Within 48 h, a discrepancy arises in the damping law of 67 steel strands without considering the effect of temperature. In addition, the discrepancy increases with time. The loss rate of each strand obeys the Weibull distribution within 48 h. The correction calculation formula can correct the lift-off test results affected by temperature and time in an actual bridge engineering test.