Study on Practical Development of Monitoring Techniques of Damage Degree and Improvement of Structural Performance of Piles

据报道，在1995年的Hyogoken-Nambu地震中，支撑建筑物的桩基损坏的例子很多。由于这些都是在地下发生的，显然会出现一些问题，如：1)挖掘工作耗费了大量的人力、时间和金钱；2)完整性测试和钻孔相机作为测量仪器不足以确认深层是否发生了损伤；3)没有健康监测系统和适当的桩损伤判断标准。本研究工作试图准备一种方便的监测技术，可以在震后不开挖的情况下立即判断桩的损伤。出于经济原因，选择碳纤维作为传感器。通过对PHC桩的多次结构试验，发现内置碳素传感器在桩身轴向布置时可以检测出弯曲裂缝，在桩周方向布置时也可以检测到剪切裂缝。在最终失效状态的情况下，由于传感器损坏，电阻达到无穷大。在此基础上，将碳传感器分别埋入混凝土灌注桩和实际建筑施工中的PHC桩中，作为实际应用的立足点，并对桩头转动性能的影响进行了分析。结果表明，桩头的非线性行为对上部结构的输入运动具有吸收能量和衰减长周期分量的作用。

Many examples of damage to pile foundations supporting buildings are reported in Hyogoken-Nambu earthquake in 1995. Because these were underground occurrence, it becomes clear to raise some problems such as, 1) It took a lot of labors, time and money in excavation work, 2) Integrity tests and bore-hole cameras used as survey apparatuses were not sufficient to confirm damage occurred in deep place, and 3) It does not exist and looks forward to a health monitoring system and an appropriate judgement standard of damage of piles.This research work trys to prepare a convenient monitering techniques possible to judge immediately damage of piles without excavation after earthquakes. Carbon fiber was selected as a sensor for economic reason. Through several structural experiments of PHC piles, it is found out that the built-in carbon sensors are possible to detect bending cracks if those are arranged in axis direction of pile, and shear cracks are also able to be detected if sensors are arranged in circular direction of pile. In the case of the final failure state, electric resistance reaches infinity because sensors are broken. And, even in the condition of deformation of pile goes back to some extent of beginning state by unloading, memory effect can be expected to show residual electric resistance.Based on these results, two examples of carbon sensors were buried in a cast-in-place concrete pile and another case in a PHC pile at construction work of real buildings as a foothole of practical application.An analysis introducing effect of rotational performace at pile head was also carried out. It can be found out as a result, that nonlinear behavior at pile head shows the effect of absorbing energy and attenuates input motion to superstructure changing into long period components.