Study Of Dynamic Response Of Broken Bridge Pile In Service

Integrity detection of pile foundation of existing structures is a difficult problem at present at home and abroad. Integrity testing of newly built pile foundation has a lot of mature detection methods such as mining for observation method, drilling core method, low strain test method, ultrasonic method, etc. But for the damage detection of the pile foundation in service, due to the existence of platform and bridge structure above pile foundation, observation method is difficult because the mining depth of the soil around the pile is very limited. Drilling core method need to drill core from the pile top and cannot be achieved. For ultrasonic detection there is no channel to install the ultrasonic transducers, for low strain test method, velocity sensors cannot be at placed the top of the pile so that vertical vibration cannot be recorded. In this paper vertical impact load is applied on the upper cap surface above the detected pile. According to the vertical velocity response of the cap surface and pile head, we analyze the integrity of the bridge pile foundation in-service.Bridge pier-cap-pile-soil explicit dynamic finite element models are built based on the ANSYS LS-DYNA. In the finite element models, impact load is applied on the cap surface and record the vertical velocity response of complete pile and cracked pile respectively. There are two kinds of pier-cap-pile-soil numerical models in the paper, respectively with six piles and with eight piles. The results show that:when impact load is applied at the cap surface on top of the pile to be detected, the stress wave go through the cap and propagate downward along the pile, similar to the principle of sonic echo method in pile integrity testing, stress wave will reflect at pile bottom or fracture surface where impedance changes greatly. From the vertical velocity response curve of pile head we can identify the reflected stress wave from pile bottom or the fracture surface, so we can know whether the pile is complete or cracked. The paper also record the vertical velocity response of cap surface, the response curve is more complicate than the pile head because of the multiple reflection of stress wave at the pile-cap interface. It is more difficult to judge the reflected wave accurately. The research work of this paper include the following contents: (1) Study the main method of in-service pile integrity detection principle at home and broad and their disadvantages. (2) Establish bridge pier-cap-pile-soil finite element numerical model, apply the transverse dynamic load, research the dynamic response of integrity pile and fracture damage pile under lateral dynamic load and identify the pile foundation integrity through lateral dynamic response curve of pile head. (3) Apply vertical load on the cap surface in the numerical model, study the dynamic response of intact pile and fracture damage pile under vertical dynamic load, identify the pile integrity through pile vertical dynamic response curve. (4) Make time-frequency analysis of pile dynamic response curve using Matlab software and judge the pile integrity by time-frequency analysis...