Civil Insight: A Technical Magazine Volume 2 | Page 13

CIVIL INSIGHT 2018 TEACHERS’ SECTION 13 Study on the Variation of Base Shear in Mass Irregular Infi lled RC Buildings Er. Mahesh Raj Bhatt Lecturer Department of Civil and Geomatics Engineering, Kathmandu University [email protected] Abstract In this study, reinforced RC frames with mass irregularity have been analysed with time history method using Gorkha-2015 earthquake as ground motion using structural analysis and design software ETABS 2000 V.16. In total, 146-story RC buildings were analysed introducing mass irregularity in each story level respectively from basement to top. Regular frame was designed as per IS 1893:2002 load combination. After the analysis, base and story shear were compared taking regular building as reference one. It is observed that the story lateral force distribution is not linear but curvilinear in nature. The story-force in which irregularity is present is higher compared to the regular one and it is further concluded that the location and magnitude of mass irregularity has signifi cant effect on the variation of base and story shear of the RC-infi lled buildings. Keywords: Base shear; Story shear; Gorkha earthquake; Masonry infi ll; Mass irregularity INTRODUCTION A structure can be classifi ed as vertical irregular if it contains irregular distributions of mass, stiffness and strength along the building height. As per (IS 1893:2002), a story in a building is said to contain mass irregularity if its mass exceeds 200% than that of the adjacent story. A large number of vertical irregular buildings exist in modern urban infrastructures. Many reasons, e.g. presence of swimming pool in particular elevation, storing of heavy mechanical equipment & machines, parking of vehicle in particular story etc. may cause the story to be mass irregular. Seismic design code has quantifi ed the magnitude of the irregularity in vertical position but not specifi ed about the effect of the location of irregularity. (Varadharajan et al., 2012)and many other researchers have concluded that the location of the irregularity in the structure is also of importance regarding the damage during earthquake excitation. As the design code of many countries does not include the location of mass irregularity, this study is intended to compare the global seismic demand in infi ll masonry RC structure with location of mass irregularity in each story. The comparison of basic seismic parameter, i.e. base shear and story shear, was studied in this particular research.