Comparative Study on R.C.C. Multistoried Building Subjected To Is: 875 (Part 3) Wind Loads Vs Hud-Hud Cyclone Wind Loads

Abstract

Indian Standard IS: 875 (Part 3)-1987 deals with wind load on buildings and other types of structures, it is under revision and draft code is also published by Bureau of Indian Standards. The recent Hud-Hud super cyclone occurred at Vishakhapatnam had a recorded wind speed of 77.5 m/s (279 kmph) as recorded by Indian Metrological Department, Visakhapatnam. Whereas the present code contemplates only a basic wind speed of 50 m/s (180 kmph) for this region. As per the observations of present cyclone, suggested wind speeds are no longer on conservative side for the safety and stability of the structures built as per the code. It is observed that a variation of 55% is observed in basic wind speed during Hud-Hud super cyclone for Vishakhapatnam region. Lot of medium to high rise buildings were designed and constructed with reference to this code. The structures which are actually designed and constructed for 180 kmph wind were subjected to a wind speed of 279 kmph. Collapse and/or damage to the structures especially to the trusses, poles, hoardings, compound walls, industrial structures and   buildings were observed during Hud-Hud cyclone.

There is an encroachment into factor of safety limits of the already designed structures. The foundation behavior and stress states are also different under increased wind loads. Hence, it is appropriate to study the available factor of safeties under the increase wind load along with other load combinations. In this paper a comparative study is made to find the effects of increased wind load due to present cyclone on a R.C.C multi-storied building compared to IS: 875 (Part 3) wind loads. STAAD. Pro finite element software is used for analyzing the structure. From STAAD.PRO software analysis results are sorted out for bending moments, axial forces in ultimate bay and penultimate bay columns at footing level and stilt floor level, which are generally critical for design. Stilt floor bending moments and shear forces in beams are compared. Inter storey drift and maximum sway of the transverse frame is also compared. The effects of various forces are studied and reported in this work.