Comparison of Seismic and Wind Analysis of G+5 and G+10 Buildings

Every multi-storey building must be designed to resist lateral loads in addition to gravity loads, and in India the two principal sources of lateral load are earthquakes and wind. The magnitude of each depends on different factors. Seismic load depends mainly on the mass of the building, its stiffness, the seismic zone, and the soil type, while wind load depends on the basic wind speed, terrain, building height, and exposed area. For a given site and building, either of these may govern the design, and designers need to know which one controls the member sizes and reinforcement. The present study compares seismic and wind analysis for two RCC buildings of different heights. Two RCC moment-resisting frame buildings, a G+5 and a G+10, with the same plan of 20 m by 16 m are modelled in STAAD.Pro. Both buildings are assumed to be located in Seismic Zone III on medium soil and in a region with a basic wind speed of 44 m/s. Seismic loads are calculated according to IS 1893 (Part 1):2016 by the equivalent static and response spectrum methods, and wind loads are calculated according to IS 875 (Part 3):2015 for terrain category 3. Dead and live loads follow IS 875 (Parts 1 and 2). The buildings are analysed for gravity, seismic, and wind load combinations as specified in IS 456:2000 and IS 1893, and the results are compared in terms of storey displacement, storey drift, storey shear, base shear, overturning moment, and forces in critical columns. The members are designed according to IS 456:2000 so that the governing load combination for each member can be identified. The results show that for the G+5 building seismic load governs, giving a higher base shear, larger storey drift, and larger column moments than wind load. For the G+10 building, the wind base shear increases considerably because of the larger exposed height and the increase of design wind speed with height, and wind becomes comparable to or greater than seismic load in the upper storeys. Seismic storey shear is concentrated near the top because of the parabolic distribution, while wind shear increases more uniformly towards the base. The study concludes that both load types must be examined for buildings of medium height and that the controlling load changes with height, zone, and wind speed. The comparison provides a practical reference for students and designers who need to decide how much attention each load type requires at the preliminary design stage of multi-storey buildings.