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

该项目的目的是获得对桩基础支撑建筑物的合理设计有用的基础材料和数据。通过对土-桩系统的复杂刚度的实验和理论研究，提出了对动力响应有显着影响的土-桩基础系统的阻尼估计和模型的呈现。通过本研究，主要得出以下几点： 1．安装在表层的浮动桩和端承桩的动态特性是通过各种参数范围内的参数研究来确定的。可见，桩的动力特性是由桩有效长度波数、桩相对土体刚度和长细比（桩长/半径）三个参数定量决定的。 2．采用最小二乘法进行递推分析，对试验结果对应的竖向和水平振动下的土桩基础系统的复刚度进行了评估，证实使用该复刚度的分析对于桩基在任意频率下的稳态响应都能给出良好的结果。 3．针对桩基的非线性分析，提出了薄层单元法，该方法由桩周围的圆柱形单元组成，以考虑土体性质沿半径方向的变化。从桩头强制激励响应结果可以看出，离地表或桩越近、激励频率越高，越容易出现非线性。 4．如上所述，采用薄层单元法对多个直径的嵌入式圆柱结构进行了分析。由于结构分析采用壳理论，可以得到壳的三个方向的位移、膜应力和弯曲应力的分布，并明确了相对于壳直径的响应分布特征。较少的

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