ANALYSIS AND DESIGN OF EARTHQUAKE RESISTANT REINFORCED CONCRETE (R.C.) CHIMNEYS

Tall R.C. chimneys are one of the specialized application structures used frequently at thermal power plants, steel mills and chemical industry etc. which are increasingly being used for discharging gas affluents at greater heights in order to control hazardous air pollution. One of the biggest advantage of R.C. chimney's is their improved vibrational performance over steel chimney's against wind and earthquake loadings. This research paper describes some of the basic analysis and design considerations for tall R.C. chimney's for earthquake induced loadings. The comparative results of a typical existing ۲۰۰ meters high tapering R.C. chimney having outside top and bo diameters as ۱۱ meters and ۲۲ meters respectively, are presented by using ACI-۳۰۷-۷۹, ACI-۳۰۷-۸۸, pusedo Static procedures and lumped mass dynamic analysis for ۰.۱۵g ground accelerations due to earthquake and has been modeled as a beam element for dynamic analysis. Comparative results indicate that dynamic analysis gives ۱,۷۱ and ۲.۷۵ times more bending moments near top and bottom levels respectively when compared with ACI ۳۰۷-۷۹ procedures. The study suggests that the safe earthquake resistant design of this category of special application structures may be based on Pseudo static analysis (FSA) after multiplying with the suggested factors as first step. These results would then be almost similar to those obtained by using lengthy and laborious Lumped mass dynamic analysis (LMDA).