Design and Analysis of Cooling Tower Is 456

Natural draught cooling towers are large thin shell structures used in thermal and nuclear power plants to reject waste heat from the condenser cooling water to the atmosphere. The tower shell is usually a hyperboloid of revolution made of reinforced concrete, supported on a ring of inclined columns at the base and stiffened by a ring beam at the top. Because of its large height, small wall thickness, and exposure to wind, the tower is sensitive to wind loading, and its design requires careful assessment of membrane forces, bending moments, and buckling. The present study deals with the analysis and design of a reinforced concrete hyperbolic cooling tower following the provisions of IS 456:2000 together with the loading guidance of IS 875 and IS 11504. A hyperbolic cooling tower of 120 m height with a base diameter of 90 m, throat diameter of 56 m, and top diameter of 60 m is considered. The shell thickness varies from 600 mm at the lintel level to 200 mm in the middle portion and increases to 300 mm near the top ring beam. The shell is supported on 40 pairs of raker columns resting on a ring foundation. The structure is modelled in STAAD.Pro using plate elements for the shell and beam elements for the columns and ring beams, and the geometry is generated from the equation of the hyperbola. Dead load, wind load, and seismic load are considered. Wind pressure is calculated from the basic wind speed and height factors of IS 875 (Part 3):2015, and its circumferential variation around the shell is represented by the Fourier cosine series given in IS 11504. Seismic load is applied using the response spectrum of IS 1893 (Part 1):2016, and temperature effects are discussed. Load combinations are formed for the limit state of collapse and serviceability as specified in IS 456:2000. The analysis gives meridional and hoop membrane forces, meridional and circumferential bending moments, and column forces for each load case. Wind is found to govern the design of most of the shell, producing tension on the windward meridian and compression on the flanks. Reinforcement in both directions is designed according to IS 456:2000 for combined axial force and bending, with minimum steel and crack-width limits applied, and the raker columns and ring foundation are designed for the governing forces. The study shows that software-based finite element analysis provides a detailed picture of force distribution in the shell that is difficult to obtain by classical membrane theory alone, especially near the lintel and top ring beam where bending is significant. The design procedure followed in the study can serve as a reference for students seeking to understand how IS 456:2000 is applied to shell structures and how wind governs the behaviour of tall cooling towers.