Behavior of rubber gasketed concrete pipe joints during earthquakes

Abstract

Thirty inch nominal diameter reinforced concrete pipelines, having standard rubber gasketed bell and spigot joints, were tested in our laboratory at Rensselaer. The joint characteristics of interest were the force deformation behavior in axial tension and compression, and the level of deformation or load leading to failure. For the case of axial extension, failure is quantified by the amount of joint extension which results in water leakage. Alternately for axial compression, failure is quantified by the magnitude of the axial compressive force resulting in crushing at the joints.

Statistical data on pipeline response parameters, namely, relative joint displacement and axial force at the joint, are obtained using Monte Carlo simulation techniques. For the case of tensile ground strain, the joints accommodate nearly all of the imposed deformation and hence are vulnerable to leakage. The computed joint displacement is compared to leakage threshold to evaluate probability of pipe failure due to leakage. For the case of compressive ground strain, the joints are subject to high compressive forces which might lead to the crushing of these joints and hence, leakage. Again, the computed joint displacement is compared to leakage threshold to evaluate probability of pipe failure due to crushing at the joints. Based on these tension and compression results, fragility curves for concrete pipelines are established. These results are benchmarked against the observed water transmission pipe damage in Mexico City occasioned by the 1985 Michoacan Earthquake.

The experimental results are implemented in a mathematical model of a long straight run of segmented pipelines. In this model, the pipe segments are discretized into a finite number of elements, each with six degrees of freedom. The surrounding soil is modeled by axial and lateral soil spring-sliders, distributed along the pipeline model. Finally, the seismic environment is quantified by seismic ground strain and ground curvature.

The purpose of this research is to present information on the seismic behavior of buried concrete pipelines. This type of pipe is widely used in both water transmission and distribution systems. In recent earthquakes, concrete pipelines experienced damage rates somewhat higher than those for other types of pipe. Furthermore, most of this damage was observed to occur at the pipeline joints. Recognizing that joints are key components, tests were conducted at Rensselaer to determine the characteristics of rubber gasketed concrete pipeline joints. This information is implemented in a mathematical model to assess the seismic vulnerability of concrete pipelines.