基于径向不变假定的变阻抗现浇大直径管桩瞬态动测响应频域解

为了分析低应变检测时有缺陷的现浇混凝土大直径管桩在瞬态集中荷载作用下的动力响应问题,基于径向不变假定建立了任意段变阻抗大直径管桩的计算模型和波动方程,采用Laplace变换法求得了波动方程的频域解析解,采用Fourier逆变换求得了时域响应.将计算结果与3维有限元、1维波动理论和3维解析解的结果进行了对比分析.研究结果表明:本文解析方法的计算结果和3维有限元结果较为接近;在90°测点,3维有限元、本文解析解和1维波动理论的速度响应差别不大.通过桩顶不同点的动力响应分析可知,入射波峰到达的时间随测点与激振点夹角不同而变化,夹角越小,到达时间越早;深度较浅缺陷反射波峰到达的时间随测点与激振点夹角而异,但达到一定深度后,缺陷反射波峰到达时间差别较小;高频干扰最小的点在夹角90°的点;对工程实测曲线的较好拟合表明该频域解析解具有一定的工程实用价值.

Study on the Velocity Responses of Large-diameter Pipe Pile with Variable Wave Impedance in Low Strain Integrity Testing

In order to obtain the dynamic response of defective large-diameter pipe pile in low strain integrity testing when subject to transient concentrated load, the computational model and wave equation of large-diameter pipe pile with variable wave impedance were established based on radial invariability assumption. The analytical solution of wave equation in frequency domain was obtained by Laplace transformation method. The dynamic responses in time domain were obtained by Fourier inverse transformation. The results of analytical solution were compared with that of 3D finite element method and 1D wave theory. The results indicated that the results of analytical solution can well match the 3D-FEM results. The velocity responses at 90°point calculated by 3D-FEM, analytical solution and 1D wave theory had little difference. The dynamic responses at different points on top of the pile showed that the arrival time of incident wave crests varied with radius angle. The smaller the radius angle, the earlier the arrival time. The arrival time of defect reflected wave crests was different among different points when depth of defect was not very deep; however, the difference was decreased when the defect was deeper. The high-frequency interference was the least at 90°point. The results of the analytical solution could well meet the measured results. It indicated that the analytical solution has some practical value for engineering.