Study On Characterization Of Wind and its Effects On Structures

Abstract

Due to the complexity of wind, all the major codes and standards of various coun- tries have considered it as Equivalent Static Wind Load (ESWL). For tall and slender structures the dynamic method i.e. Gust Factor Method, originally proposed by Dav- enport(1967) for the estimation of wind load on structure, is based on the Displace- ment based Gust Loading Factor (DGLF). Zhou and Kareem (2003) have highlighted that the Moment based Gust Loading Factor (MGLF) offers a more realistic way of distribution of the ESWL along the height of the building compared DGLF. The present study focuses on understanding the wind characterization method- ology of DGLF and MGLF in detail. It also aims towards comparing DGLF based existing Indian code IS:875 (Part-III)-1987, the method proposed in IS 875 Draft code by Bhandari et. al. (2002) and the MGLF procedure proposed by Zhou and Kareem(2003). A 30 storey, wind governed, Reinforced Concrete (R.C.) symmetric building is considered. Response quantities like Lateral Wind Force, Base Shear, Overturning Moment, Displacement and Storey Drift are calculated and compared using the above mentioned three approaches. Also a parametric study has been con- ducted by varying height of the building considering 40,50 and 60 storeys to compare DGLF and MGLF method and the same quantities have been compared with the addition of comparison of column reinforcement.The MGLF method gives maximum values of lateral forces as compared to other two methods. As a result it is observed that application of MGLF increases the column reinforcement on an average by 30% for all the three buildings. Further, the application of the MGLF method is extended to a problem of a steel chimney and the results are compared with the existing design code IS 6533(Part 2)-1989. In case of chimney too, the implementation of MGLF yields higher results of lateral forces and results in higher thickness of the stack plates which results in increase in steel quantity.