夹片咬合力测试方法

为研究采用拉脱法检测预应力钢绞线受力时, 张拉力荷载测试曲线突变段和夹片咬合力的关系, 在夹片脱开时, 采用电阻式压力传感器高频采集技术测试了预应力混凝土梁锚具下方和锚具外侧钢绞线的受力, 共测试了20个样本; 设计了夹片咬合力测试方案, 共测试了326个样本, 并进行了统计分析, 建立了考虑张拉力的夹片咬合力计算公式; 通过37个样本的验证性测试, 研究了咬合力修正结果的测试精度; 在实际工程中检测了257个样本, 并将实测结果与提出的公式计算结果进行对比。研究结果表明: 当钢绞线伸长超过4.5 mm时, 夹片会脱离原有咬痕, 而实际测试中夹片脱开时会及时停止张拉, 因此, 拉脱法测试不会改变预应力钢绞线锚下有效预应力, 不会影响工程质量; 夹片安装时, 若夹片与锚杯锥孔不完全贴合, 会使夹片在横向产生较大的弹性挤压力, 形成附加摩擦力, 该摩擦力需要在夹片退出至与锚杯分开时才能完全消失, 此时锚外张拉力变化不明显, 因此, 拉脱法测试所得张拉力曲线中峰值拉力后的下降段斜率存在离散性, 与夹片安装精度有关; 拉脱法测试中夹片与锚杯的咬合力由锚下和锚外瞬态内力重分布累加组成, 提出的夹片咬合力计算公式能剔除由夹片与锚杯间咬合力产生的测试误差, 可使测试精度提高6.78%;实际工程现场实测夹片咬合力大于拉脱法测试所得张拉力曲线突变段, 因此, 采用拉脱法检测预应力钢绞线时, 锚下有效预应力为拉脱法测试所得张拉力曲线峰值与咬合力的差值。

Test method of clip bite force

To study the relationship between the mutation segment of tension test curve and the clip bite force when using the lift-off method to test the force of prestressed steel strand, the high-frequency acquisition technique in the resistive pressure sensor was used to test the prestressed steel strand forces of a prestressed concrete beam under and outside the anchorage when the clip disengages. A total of 20 samples were tested. The clip bite force test scheme was designed. A total of 326 samples were tested and the statistical analysis was performed. The calculation formula for the clip bite force considering the tension was established. Through the verification test of 37 samples, the test accuracy of bite force correction results was studied. 257 samples were tested in the actual project, and the test results were compared with the proposed calculated formula results. Research result shows that the clip will break away from the original bite mark when the steel strand extends more than 4.5 mm. However, when the clip disengages during the actual test, the tension will be stopped in time, so the lift-off test will not change the effective prestress of prestressed steel strand under the anchorage and affect the project quality. When installing the clip, if the clip does not completely fit the taper hole of socket, the clip will have a large elastic pressing force in the lateral direction to form an additional friction force. The friction force will completely disappear when the clip is separated from the socket. The change of tension outside the anchorage is not obvious at this moment, so the slope of descending segment of tension test curve obtained by the lift-off method has a dispersion after the peak tension, and it is related to the clip installation precision. The bite force of socket in the lift-off test consists of the transient internal force redistributions under and outside the anchorage. The proposed calculation formula for clip bite force can eliminate the test error caused by the bite force between the clip and the socket, and improve the test accuracy by 6.78%. The test bite force in the actual project is larger than the mutation segment of tension test curve obtained by the lift-off method. Therefore, when using the lift-off method to test the prestressed steel strand, the effective prestress under the anchorage is the difference between the peak value of tension test curve obtained by the lift-off method and the bite force.