Fundamental Study on Dynamic Damping Characteristics of Soil Ground at a Water Front

本课题的目的是为合理设计桩基支撑的建筑提供基础资料和数据。通过对土-桩复合刚度的试验和理论研究，提出了对动力响应有重要影响的土-桩基础系统的阻尼估计和模型。从本研究中可以总结出以下几点：在较宽的参数范围内，通过参数化研究确定了安装在地表地层中的浮桩和端桩的动力特性。由此可见，桩的动力特性是由桩有效长度的波数、桩对土的刚度和长细比（桩长/半径）3个参数定量确定的。采用最小二乘法对桩-土基础体系在竖向和水平振动下的复刚度进行了递推计算，得到了与试验结果相对应的复刚度分析结果。针对桩基础的非线性分析，提出了考虑桩周围土体性质在半径方向上变化的薄层单元法。从桩顶强制激励的响应结果可以看出，越靠近地面或桩身，激励频率越高，越容易非线性化。采用上述薄层单元法对几种直径的内嵌圆柱结构进行了分析。由于采用壳理论对结构进行分析，可以得到壳体三个方向的位移、膜应力和弯曲应力的分布，明确了壳体直径对应的响应分布特征。少

A purpose of this project is to obtain fundamental materials and data useful for the rational design of buildings supported by the pile foundation. Estimation of damping and presentation of a model of soil-pile foundation system which significantly effects on the dynamic response are proposed through the experimental and theoretical investigations on the complex stiffness of soil-pile system. From this research, followings are summarized.1. Dynamic charcteristics of floating and end bearing piles installed in surface strata are determined by parametric study within a wide range of parameters. It becomes clear that the dynamic characteristics of pile are determined quantitatively by three parameters, i.e. wave number for effective length of pile, stiffness of pile to that of soil and the slenderness ratio(pile length/radius).2. Complex stiffness of soil-pile foundation system in vertical and horizontal vibration corresponding to the experimental results has been evaluated by recurrence … More analysis which adopts the least square method, the analysis using this complex stiffness is confirmed to give good results for the steady state response of pile foundation at any frequency.3. Concerning to the nonlinear analysis of pile foundation, thin layr element method which consists of cylindrical elements around the pile is developed to take into account the variation of soil properties in the radius direction. From the result of response due to forced excitations at the pile head, it is found that the nearer to the ground surface or the pile and the higher excitation frequency, the easier to become nonlinear.4. Embedded cylindrical structure with several diameters are analyzed by the thin layr element method as in the above. Since the analysis of the structure is dealt with the shell theory, distribution of displacements in the three directions, membrane stress and bending stress of the shell can be obatined and the distribution characteristics of responses corresponding to the diameter of shell become clear. Less