Study on Pile Head Joint by Energy Absorbing Method

对实际尺寸的桩头节点试件进行了循环水平荷载试验。以直径50cm的PHC桩为试件，端面焊接8根螺柱，烧入底板5cm。螺柱是用铅捆扎起来的。将基础板固定在楼板上，在距基础板表面1.75m处，在98OkN的轴向荷载下，对桩施加循环水平荷载。螺柱杆在循环水平荷载作用下，在桩头摇摆运动的作用下，在铅的作用下，螺柱杆在铅的作用下运动，从而产生了铅的阻尼效应。测试结果如下：荷载-位移关系在桩的短期允许弯矩所对应的荷载水平前保持线性状态，超过该水平后变为s型宽滞回线，直至达到极限状态，即铅的阻尼作用表现明显。在桩头位移28mm处，底板表面出现裂缝。通过这些裂缝的发展，产生其他裂缝并相互连接，最终达到桩周表面混凝土完全脱落的状态。采用粘弹性材料对2个剪切土箱中层流桩支撑的箱型上部结构进行了振动台试验，其中一种是桩头节点固定工况，另一种是阻尼工况。主要试验结果如下：阻尼器模型下的固有频率和响应放大也比固定模型下的固有频率和响应放大要小，阻尼器效应明显。在随机波输入和地震输入运动情况下，扫描试验也出现峰值。随着输入运动强度的增大，模型地面的非线性效应也越来越明显。

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.