Evaluation and Retrofitting of Shaft Supported Water Tanks

Abstract

Water tanks are one of the essential lifeline public service facilities and their post earthquake functionality is essential. There is a prior need to adapt for accurate analysis and simple yet efficient aseismic design method for elevated tanks, as these structures are primarily vulnerable to severe earthquakes due to their configuration involving large mass concentrated at the top supported on relatively slender stagings. The poor performance of such critical facilities during recent seismic events in the country required careful scrutiny of their designs, construction quality and their post earthquake performance. Various photographs of existing shaft supported water tanks which were distressed are presented to illustrate generalized distress in shaft supported water tanks. A brief review of present code for seismic analysis and design of elevated reinforced concrete water tanks IS: 1893-1984 and Proposed draft for IS 1893 (Part II) has been made. A case study of an intze tank resting on a cylindrical shaft type staging has been designed using the present code IS: 1893-1984 and the Proposed Draft of IS 1893 (Part - II). Proposed draft for IS 1893 (Part II) has been reviewed and its level of forces are compared to that of IS 1893: 1984 for elevated shaft supported tanks. Non destructive testing tests such as Rebound hammer test and Ultrasonic pulse velocity test, Partial destructive test such as Core test, depth of carbonation etc were carried out to get the complete details of concrete quality and the present strength of concrete. Repair and retrofitting measures are given on the basis of design values of IS: 1893- 1984 and Proposed draft of IS: 1893-(part-II). Basic cost analysis for repair method (Epoxy grouting) and strengthening method (concrete Jacketing) is also carried out for the same case study.