Study on Pile Head Joint by Energy Absorbing Method

对实际尺寸的桩头接头试件进行了循环水平荷载试验。试件为直径50 cm的PHC桩，端面焊接8根螺柱，基础底板烧制5 cm。螺柱用铅捆扎起来。将地基板固定在地基板上，在距地基板表面1.75m处，在98okN的轴向荷载作用下，对桩施加水平循环荷载。将螺柱用铅捆绑的原因是为了期望铅的阻尼器作用于桩顶在水平循环荷载作用下的摇摆运动，从而使螺柱在铅中移动。荷载-位移关系在桩的短期允许弯矩所对应的荷载水平处保持线性状态，超过该水平后，变为S形状的宽滞回钢索，直至极限状态，即铅的阻尼力效应明显显现。在桩头位移28 mm的台阶处，基板表面出现裂缝。通过这些裂缝的扩展、其他裂缝的产生和相互连接，最终形成桩周表层混凝土完全剥落的状态。对两个土箱剪切条件下的层流桩支承的箱形上部结构进行了振动台试验，其中第一个是桩头固定条件，第二个是采用粘弹性材料的阻尼性条件。主要试验结果如下：阻尼器模型的自振频率和反应放大系数也低于固定模型，体现了明显的阻尼器效应。在随机波输入和地震输入运动的情况下，也出现了扫描试验的峰值。输入运动的速度越大，模型地基的非线性影响就越大。

A cyclic horizontal load test was performed on a real size test specimen of pile head joint. A PHC pile with 50cm in diameter, welded 8 stud bars to end face and burned 5 cm into foundation slab, was used as test specimen. Stud bars are bound up by lead. The foundation slab is fixed to the floor, and cyclic horizontal load is applied to pile, under the axial load of 98OkN, at 1.75m up from the surface of foundation slab. The reason why the stud bars are bound up by lead is to expect damper effect of lead that the stud bars are moving in lead under the rocking motion of pile head by cyclic horizontal load.As a test result, the following is obtained. Load-displacement relation keeps linear state up to the load level corresponding to the short-term allowable bending moment of pile, but exceeding that level, changes to S-shaped wide hysteresis roop until the ultimate state, i.e., damper effect of lead is displayed clearly. Cracks are observed on the surface of foundation slab at the step of displacement of pile head 28mm. By progressing these cracks, producing other cracks and connecting mutually, the final state becomes the surface concrete surrounding the pile comes off totally.A shaking table test was also performed for 2 box-type superstructures supported by laminar piles in shearing soil-box, the first one of which is fixed condition at pile head joint and the second one is damper condition by using visco-elastic material. The main test results are as follows ; Natural frequency and response amplification are also lower in the case of damper model than the fixed model showing the damper effect clearly. The peak of sweep test appears also in the case of random wave input and earthquake input motion. As the revel of input motion is larger, effects of non-linearity of model ground appears still more.