Analysis On Seismic Response Of Underground Water-supply Pipeline

Underground water-supply pipline covered every place of human environment, which was called city arterial of blood transfusion. With the rapid progress of city modernization, people have a increasing demand of water supply. Once the water can not be supplied in time, it will cause irreparable loss for all kinds of fields. Earthquake is the most important reason for leading piping system damage, in recent years, serious earthquake always leaded to large areas of failure on pipline, which will trigger to secondly disaster such as fire, infectious diseases and so on. Therefore, improving the seismic performance of piplines is a significant task.Researches on the seismic performance of underground pipeline were paid more attention to pipe-body damage. However, according to the earthquake survey, joint damage seems to be the main form of the earthquake damage of underground piplines. Nowadays, more flexible socket joints were used in engineering. Thus, it is important for science and engineering to take a research on the seismic performance of flexible joints. ANSYS software was used for the analysis of the seismic response of pipline with flexible joints. It provides the theory basis for the design of underground pipeline with flexible joints. The main research contents and the main conclusions of this paper are as described below.The numerical model of the underground pipeline with flexible joints and covered by soil was built by ANSYS finite element analysis program,which was composed of three pipe section bodies with the length of 9m and 2 socket flexible joints and surrounding soil, pipe body material was nodular cast iron. According to the seismic design code, III site soil and classical El-centro seismic waves were selected. Meanwhile,7-degree seismic intensity was considered. Moreover, the basic response of pipeline under earthquake were studied, and the effect factors such as pipe diameter, single pipe length, buried depth, seismic intensity on the seismic response of underground pipeline were derived, adjusting the peak acceleration of seismic waves,with shear wave and longitudinal wave being exerted on specified place by means of big mass point way.(1) The main damage form of underground water supply pipeline is that socket flexible joint is pulled and tube rupture. Through the numerical simulation, the calculation data of the displacement of the most dangerous point of joint and the stress of the most dangerous point of tube were extracted. The results showed that, on III site soil and 7 degree intensity, socket flexible joint displacement was almost 63mm, and the pipeline will leak, the most stress of the tube was 78MPa, which is far from the ultimate strength of nodular cast iron. Flexible joint will decreas the stress of tube significantly.(2) Pipe diameter has a certain influence on seismic performance of underground water-supply pipeline with flexible joint. As the diameter increase, the Mises stress of tube and displacement of socket joint will reduce. So compared to the pipline of big diameter, the pipline of small diameter is easier to be destroyed. During the seismic design, after meeting other conditions, chosing the diameter as big as possible can improve pipeline's seismic performance in some degrees.(3) Buried depth has a certain influence on seismic performance of underground water-supply pipeline with flexible joint. As the depth increase, the Mises stress of tube and displacement of socket joint will reduce. At the same time, considering laying pipelines work, the buried depth should not be too deep. Choose burying piplines in appropriate depth on the premise of safety.(4) Pipe section length has a certain influence on seismic performance of underground water-supply pipeline with flexible joint. As the pipe section length increase, the overall stiffness of underground pipline has a correspondent increase, which will cause the correspondent increase of the Mises stress of pipe body and the displacement of socket joint in the seismic. Consider the connect workload during laying the pipline, pipe section length length should not be too short, and the length of single underground pipe with the diameter of 200mm is suitable for 9m.(5) Seismic intensity is very important to seismic performance of underground water-supply pipeline with flexible joint. As the intensity increase, the Mises stress of tube and displacement of socket joint have a sharp increase, which means the potential risk of pipline leak. The results showed that, under the action of 6-degree intensity seismic, the joint of pipline will hardly leak. Under the action of 7-degree intensity seismic, the joint of pipline will cause part of leak because of the displacement of joint. Under the action of 8-degree intensity seismic, the joint will almost pulled out completely, and the transfer function of water-supply pipline will totally lost.