Analysis of high rise building with soft storey heights and approaching methodology

Abstract

Earthquakes are natural hazards under which clisasters are mainJy caused by damage or collapse of buildings and other man-made sn-uctures. Due to accommodation of vehicles and their movements at ground levels infill walls are generaUy avoided. which creates soft storey effect. It should be noled that 70 to 80 % of buildings of urban areas in India fall under the classification of soft storey. This soft storey is also called as Open ground storey or Weak storey. It is a typical feature in the modem multi-storey constructions. Such features are highJy undesirable in buildings built in ei micaJly active areas; this ha been verified in numerou experiences of strong shaking during the past earthquakes. The majority of building that failed during the Bhuj earthquake (200 I) and Gujarat earthquake were of the open ground storey type. The collapse mechanism of such type of building is predominantly due to the formation of soft-storey. As per Indian Standard JS 1893: 2002, the Columns and Beams of the open ground storey are lo be designed for 2.5 time the torey hears and moments calculated under eismic load of bare frame . This Multiplication Factor value however does not account for number of storeys, number of bay • type and number of infill walls present, etc, and hence it is independent of all of the above factors. The multiplication factor of 2.5 is not reaJistic for low rise buildings. This calls for an assessment and review of the code recommended multiplication factor for low ri e open ground storey builcling . Therefore, the objective of this tudy i defined as to check the applicability of the multiplication factor of 2.5. This study includes analysis of (G+7) RCC Framed building analysed u ing Seismic Coefficient Method (SCM) as per IS 1893: 2002. Io modelling the masonry in.fiJJ panels, Equivalent diagonal Strut method is used. This study basicaJJy includes Four models namely, Frame without masonary infill effect (Bare frame). Masonary lnfill frame, Frame with Tie-beam (Tie-beamed frame) and Frame with Bracing. (Braced frame) which are analy ed for Soil type I (Hard) and Soil type Ill (Soft) considering time period for seismic analysis as per Program calculated and as per Coda! provision. The response of columns in Open ground storey are discussed and conclusions are made in this study analysed on ETABS software.