Study on Pile Head Joint by Energy Absorbing Method

对桩头接头实际尺寸的试件进行循环水平荷载试验。试件采用直径 50cm 的 PHC 桩，端面焊接 8 根螺柱，烧入基础板 5cm。螺柱用铅绑扎。基础板固定在地面上，在距基础板表面1.75m处，对桩施加水平循环荷载，承受98OkN的轴向荷载。螺柱杆被铅束缚的原因是期望在循环水平荷载的桩头摇摆运动下螺柱杆在铅中移动的铅的阻尼效果。作为测试结果，得到以下结果。荷载-位移关系在桩的短期许用弯矩对应的荷载水平之前保持线性状态，但超过该水平时，变为S形宽滞回圈，直到极限状态，即铅的阻尼效应清晰地显示出来。桩头位移28mm时，基础板表面出现裂缝。通过这些裂缝的发展，产生其他裂缝并相互连接，最终的状态是桩周围的表层混凝土完全脱落。还对剪力土箱中层状桩支撑的2个箱式上部结构进行了振动台试验，第一个为桩头接头固定状态，第二个为粘弹性材料阻尼状态。主要测试结果如下：阻尼器模型的固有频率和响应放大率也低于固定模型，清楚地显示了阻尼器效果。扫描测试的峰值也出现在随机波输入和地震输入运动的情况下。输入运动幅度越大，模型地非线性的影响就越明显。

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.