列车荷载在地基中引起的应力响应分析

ANALYSIS OF STRESSES IN TRAIN-INDUCED GROUND

用弹性地基上Timoshenko梁及其在移动荷载作用下的动力解计算得到地基表面与路堤之间的反力。将其视为作用于地基表面的荷载,以单位移动荷载引起的半空间地基内部应力解为基础,对反力在作用空间上进行积分,得到了列车速度小于地基中Rayleigh波速时,列车荷载在地基中引起的稳态应力响应解答。通过与列车振动现场测试结果(路堤位移和速度)的比较,证明了所采用模型的合理性。给出了应力及其分布随时间和空间坐标的变化,分析了应力的特性及分布规律,发现列车经过时在地基中产生的动应力是一种以压应力为主的循环荷载。动应力的空间分布与地基表面作用静力荷载(如条形荷载)产生的应力分布相似,但随列车运动而呈动态变化。还研究了半空间地基的土性和列车速度对应力的影响,发现剪切模量对应力的影响与车速有关,列车速度对应力分布的影响很大,尤其是当速度比超过0.6时,而泊松比仅对水平应力影响较大。

Based on the theory of Timoshenko beam on elastic foundation and its dynamic solution under moving loads, the train-induced reaction forces between ground surface and embankment are calculated. Exerting the reaction forces on the ground surface, the corresponding steady-state stresses in ground are obtained by integrating the basic solution of a moving point load on the surface of an elastic half-space. The results are valid only for train speed lower than Rayleigh wave velocity in ground. Compared with the in-situ testing results of train vibration, including embankment displacement and velocity, it is shown that the presented model is reasonable. The variation of stresses with spatial co-ordinates and time is presented. Characters and distribution patterns of stresses are studied. The dynamic stresses seem to be a kind of particular cyclic loads, which are mainly compression stresses. The distribution of dynamic stresses is similar to that of stresses induced by static load (such as strip load) on the ground surface, but changes with train motion. The influence of ground properties and train speed on stresses is also presented. It is found that the influence of shear modulus on stresses is dependent on train speed, and the influence of Poisson's ratio on horizontal stresses is significant. The train speed also affects the stress distribution greatly, especially when speed ratio is over 0.6.