Effect of Micro and Macro Modeling of Infill on Magnification Factor of Open Ground Storey

Abstract

The multi-storied structures that are still prevailing in metropolitan extents have open ground story (OGS) buildings as an inevitable feature, basically to accommodate parking or reception lobbies. OGS framed structures, with the soft storey at the ground floor are generally analyzed in practice, ignoring infill wall stiffness. Therefore the shear force and bending moment of the column of a ground story should be magnified according to Indian standards. IS1893-2002 recommends a magnification factor (MF) of 2.5 to be applied on BM and base shear of ground story columns. The present study attempts to estimate the MF, for the Micro and Macro infill model. Macro infill is modelled by referring to two equations given by Stafford Smith, and Paulay-Priestley, whose results are compared and concluded that by using the Paulay and Priestley equation, the stiffness of structure has increased leading to higher base shear than using the Stafford equation. It is also clear that Pauley-Priestley is an easier method and adaptable. The study is further continued by nonlinear analysis and accounting for the comparison of macro-infill and micro-infill. Response spectrum (RSA) and nonlinear pushover analysis (NPA) is carried out for a five-storey building with footing level included for two types of infill wall arrangements using ETABS. The results of RSA and NPA indicate that MF is greater for the Micro infill model than micro infill model. And also results of NPA indicate that MF is lesser than the RSA. The investigation results express that there is no requirement for applying MF to soft-storey beams, as expanded requests because stronger beams would additionally build the seismic demands on the columns. Indian Standard has recommended higher value for low-rise buildings, it is also important to analyse OGS structures as infilled frames considering stiffness rather than the bare frame.