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场地土层的自振频率是场地土的重要动力特性之一。为避免结构物与场地地基的共振效应,工程设施的固有频率应尽量避开地基的固有频率。在传统的基于集中质量矩阵的剪切质点系法(集中质量法)的基础上,发展了基于一致质量矩阵的剪切质点系法。在此基础上,对利用剪切质点系法求解水平层状场地自振频率的精度的影响因素进行了分析,主要考虑了土层分层特性、质量矩阵形式以及材料阻尼3个影响因素,分析表明:分层数越多,计算结果越接近真实解,从实际工程角度出发,分层数超过三层时可不再细分;在层数相等的情况下,层厚对计算结果精度的影响甚微;一致质量法的计算结果要优于集中质量法,且表现出上限解性质;在通常小阻尼情况下,阻尼对自振频率的影响很小。
The natural frequency of site soil is one of the important dynamic characteristics of site soil. In order to avoid the resonance effect between structure and foundation, the natural frequency of engineering facilities should be as far as possible to avoid the natural frequency of foundation. On the basis of the traditional shear mass point method based on the concentrated mass matrix (focused mass method), the shear particle point method based on the uniform mass matrix is developed. On this basis, the influencing factors of the accuracy of solving the natural frequencies of horizontal layered sites by using the shear-point method are analyzed. The factors of stratification, mass matrix and material damping are mainly considered, and the influencing factors are analyzed. The results show that the more the number of layers is, the closer the calculation results are to the true solution. From the perspective of practical engineering, the number of layers can be no longer subdivided when the number of layers exceeds three. In the case of equal number of layers, The results of the consistent mass method are superior to those of the mass method, and show the properties of the upper bound solution. In the case of small damping, the damping has little effect on the natural frequency.