SEISMIC ANALYSIS AND DESIGN OF ELEVATED WATER TANK STAGING

Abstract

This thesis investigates the seismic analysis and design aspects of R.C. frame type elevated water tank staging. Performance of such staging in past earthquakes has been reviewed. The bracing girder of such tanks are particularly vulnerable to shear failure. The Indian code provisions for a seismic design of elevated water tanks have been reviewed. The code provides for rather low seismic design force for these structures due to the absence of suitable value of performance factor. It is shown that the conventional method which assumes the bracing girders to be infinitely rigid for staging stiffness calculation is very inaccurate. Four different approximate methods have been used to analyse two existing tanks and the results have been compared with 3D stiffness matrix method analysis. One Is the conventional method, which assumes braces to be infinitely rigid. And the other three approximate methods are based on the portal frame and moment distribution methods. The general practice among the designers is to neglect the effect of staircase on the dynamic response of the water tank staging while designing the structure for lateral loads. For some particular type of staircases configuration this cannot be done. For those cases where the staircase is built on separate columns the contribution of staircase columns to the overall stiffness of the staging is substantial. The above tanks were studied to examine the effect of staircase on the dynamic response of the staging. Torsional effect of the staircase has been studied by approximate as well as 3D analysis.