Analysis and Design of Reinforced Concrete Chimney

Abstract

A chimney is a means by which waste gases produced due to industrial processes are dis- charged to the atmosphere. Height of the chimney is kept such that the gases get diluted due to atmospheric turbulence. Chimney is particularly susceptible to the wind pressures, and hence, it is important to correctly estimate the design wind loads. Chimney is a vertical cantilevered shell pierced by openings where necessary and subjected to large temperature gradients. The Indian Standard, IS: 4998 (Part 1) 1992 lays the provisions for the analysis and design of chimney structures. Apart internationally, various codes namely, ACI 307 08, CICIND 2001, EUROCODE 8 (Part 6) are widely used for analysis and design of chimney structures. The prime focus of the present major project work is to study the behaviour of chimney structure under the effect of wind loads, earthquake loads and temperature gradients. Anal- ysis of the chimney is carried out considering typical loads, as specified in IS: 4998 (Part 1) 1992 by developing excel sheets. Chimney has been modeled in STAAD.Pro using the lumped mass modeling approach, to calculate dynamic properties useful for seismic as well as wind analysis. Recently BIS has published draft code IS: 4998 (April 2013). The provisions of the Draft Indian Standard are studied and compared with the provisions of the existing Indian Stan- dards viz. IS: 4998 (Part - 1) 1975 and IS: 4998 (Part - 1) 1992. Apart, a parametric study has also been carried out for an RCC chimney by keeping its height constant and varying the seismic zone and wind speeds. It is found that in locations with high seismicity the earthquake forces govern the design.