传感器黏结剂对低应变测试曲线的影响

Impact of accelerometer adhesive on low strain testing curves

为了分析黏结剂对桩顶测试曲线的影响,考虑黏结剂自身的刚度和阻尼,建立黏结剂与传感器组成的双自由度系统振动模型.利用拉普拉斯变换,求得传感器振子和底座位移差的导纳函数.利用已知的桩顶速度响应函数、卷积定理以及傅里叶逆变换,求得正半弦脉冲激励作用下传感器电荷输出的半解析解.利用所得解,根据传感器电荷输出与桩顶速度响应的关系,分析黏结剂材料的刚度及阻尼对传感器输出电荷曲线及实测桩顶速度曲线的影响.结合完整桩和缩颈桩2个算例进一步分析黏结剂对桩顶测试曲线的影响,并将理论曲线与实测曲线进行对比.结果表明:所得理论解与实测速度的响应曲线一致,传感器黏结剂自身刚度和阻尼的减小均会大大增加桩身反射信号的判别难度.

A vibration model of the two-degree freedom system consisting of accelerometer and adhesive was established to analyze the influence of the adhesive on the test curve at the top of pile,considering the stiffness and damping of the adhesive.An admittance function of the difference between the displacements of the accelerometer oscillator and base was analytically derived in Laplace transform space.A semi-analytical solution was derived for the electric charge output of the accelerometer subjected to a semi-sine wave exciting force,with the use of the already known velocity-response function at the top of pile,the convolution theorem and the inverse Fourier transform.The obtained solutions were used to analyze the influences of stiffness and damping of accelerometer adhesive on the relationship between the charge output of the accelerometer and the velocity-response at the top of pile.Two examples were selected to further analyze the influences of accelerometer adhesive on velocity-response curve at the top of pile：one was a intact pile,and the other was a defective pile.The theoretical results were also verified experimentally with good agreement between the theoretical and the experimental velocity response curves.Both the decrease of coefficient of stiffness and damping of the adhesive would lead to great difficulty in distinguishing the reflection signal of pile.