Development of pile foundation with high ductility aseismic joints

在本研究的第一阶段，我们开发了高延性抗震接缝(HDAJ)桩。我们进行了弯曲试验，以研究桩的弯矩-挠度关系。在此基础上，开发了大变形分析的非线性有限元程序。通过对实验结果的模拟，验证了非线性有限元方法的有效性。接下来，我们对原有的HDAJ桩(X型)进行了改进，使其具有更高的延性(Y型)，并进行了参数研究，考察了液化引起的地面大变形时，接头类型(X型、Y型)、层厚、承台连通性、桩端埋深等因素对溢流桩的影响。在所有情况下，我们发现HDAJ桩对于液化引起的较大的地面侧向位移是有效的(Y型比X型更有效)。第二阶段，对HDJA桩进行了动力分析，研究了其地震反应特性。HDAJ桩比顺序桩具有更大的柔性，因此HDAJ桩的地震反应可能比顺序桩大。这就是我们进行地震反应分析的原因。但HDAJ桩在强震作用下的最大加速度、最大速度和最大位移等响应并不比顺序桩大。此外，桩的最大弯矩也大大降低。这意味着HDAJ桩在强震时也是有效的。

We developed a High Ductility Aseismic Jointed (HDAJ) Pile at the first stage of this study. We performed bending tests to investigate the bending moment-deflection relationships of the pile. Then we developed nonlinear finite element analysis program which can analyze the large deformation analysis. The validity of the nonlinear FEM was conformed by simulating the experimental results. Next, we modified the original HDAJ pile (X-type) to give more ductility (Y-type).We performed parametric study to examine the effect of splicer types (X-type, Y-type), stratum thickness, pile cap connectivity, pile tip embedment depth etc.on the spilced piles when subjected to large ground deformation caused by liquefaction. In all cases, we found that HDAJ piles were effective (Y-type is more effective than X-type) compared with ordinal pile for liquefaction-induced large lateral ground displacements. At the same time, we found that the failure mechanism of piles could be categorized into 6 patterns.In the second stage, we performed dynamic analyzes of the HDJA piles to investigate the seismic response characteristics. The HDAJ piles are more flexible than ordinal piles, therefore, the seismic responses of HDAJ may greater than those of ordinal piles. This is the reason why we performed the seismic response analyzes. But the responses, such as the maximum acceleration, velocity and displacement, of HDAJ piles to strong earthquake motions were no more than those of ordinal piles. Besides, the maximum bending moment induced in piles were greatly reduced. This means that the HDAJ piles are also effective during strong earthquake motions.