Evaluation of Magnification Factors for Open Ground Storey Buildings Using Nonlinear Analyses

Abstract eng:
Open Ground Storey (OGS) framed buildings, with soft-storey at ground storey are commonly analysed in practice, ignoring the infill wall stiffness (linear ‘bare frame’ analysis). Design codes impose a magnification factor (MF) on the design forces in the columns of the ground storey, based on such analysis. The present study attempts to estimate typical variations in MF, by modelling infill walls using Smith and Carter (1961) for linear analysis and Crisafulli (1999) for nonlinear analysis, accounting for the variability of compressive strength and modulus of elasticity of infill walls. Response Spectrum Analysis (RSA) and Nonlinear Dynamic Analysis (NDA) are carried out on a four storeyed and a seven storeyed building, for various infill wall arrangements. The results from RSA (linear analysis) indicate MF values in the range 1.04-1.13, for the four storeyed building and 1.11-2.39 for the seven storeyed building. However the results of NDA (nonlinear analysis) including hysteresis effects in frame and infill, suggest that there is no need for applying MF to low-rise building frames. In the case of the seven-storeyed building frame, values of MF in the range 1.14 to

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