Effects of presence of nearby structures on ground vibration attenuation along response line

本研究分为两个课题。在第一个主题中，研究了当来自相邻源的行波激发时，沿着在两个或三个结构附近建立的响应线的振动衰减。在考察了结构之间的分离距离和方向对振动衰减特性的影响后，观察到以下结果。在结构共振附近的低频范围内，有结构的地面振动比无结构的地面振动大。在高频范围内，多结构下位于结构下游的响应点的振动比单结构下的响应点的振动小。当结构与响应线成直角布置时，结构运动激发的散射波与自由场中的波之间的相位差似乎对响应线沿线的振动评估起着重要作用。在第二部分中，采用薄层单元和离散波数法模拟了移动谐波荷载作用下的地面振动。此外，还提出了一种近似计算路旁地面振动的方法，该方法将车辆动载荷展开为Fouvier级数，并将谐波载荷的解与载荷的频率分量相乘，从而求得其解的叠加。实例应用结果表明，动荷载的移动效应在距离车道较近的测点处出现。然而，随着与车道的距离变大，这种效应会迅速衰减。

This research is divided into two subjects.In the first subject, the vibration attenuation along a response line established near two or three structures is studied when excited by traveling waves from an adjacent source. The following is observed after the examination of the effect of the separation distance and orientation between structures on the characteristics of the vibration attenuation. The ground vibration around structures becomes larger than the vibration of ground without structures at low frequency range near the resonance of structures. In the range of high frequencies, the vibration of response points located downstream of the structures in case of multiple structures becomes smaller than the one in case of single structure. In case that structures are arranged at the right angle to a response line, it seems that the phase difference between the scattered wave excited by the motion of structures and the wave in the free field plays an important role in the assessment of the vibration along the response line.In the second subject, a thin-layred element and discrete wavenumber method is applied to simulate the ground vibration by a moving harmonic load. Moreover, an approximate method is proposed to calculate the ground vibration at a wayside in which a vehicle dynamic load is expanded in the Fouvier series and the solutions for harmonic loads are superposed by multiplying them by the frequency components of loads. As the results of the application to several examples, it is found that the moving effect of a dynamic load is appeared at measuring points in the near distance from the traffic lane. However, this effect decays rapidly as the distance from the lane becomes larger.