Seismic Design Evaluation of 10 Storeyed RC Building Using Nonlinear Analysis with Open Ground Storey Located in Medium Seismic Zone of India

Abstract

In this paper authors have attempted to bring out the possible shortcomings in the analysis, design and seismic evaluation of commonly adopted OGS buildings in urban India and have suggested a suitable modelling strategy to be adopted in nonlinear analysis for satisfactory performance at demand earthquake. Nonlinear Time History (NTH) and Nonlinear Pushover Analysis (NSP) are performed on 10 storeyed OMRF RC building located in medium seismic zone designed as per IS codes for DBE. Three building models depicting the stiffness representation are analyzed and designed whereas nonlinear analyses (NSP and NTH) are performed considering four different scenarios depicting the lateral load pattern along the building height and plastic hinge properties for the frame elements and infills. The findings of the study reveals that the lateral forces obtained using response spectrum analysis and consideration of infill stiffness with additional walls in the corner bays of ground storey along with user defined hinges, will closely represent the actual behavior of the building at demand earthquake and thus will aid in better estimation of safety levels of OGS building. This is significant because open ground storey buildings are typically designed as bare frames and while carrying out nonlinear analysis equivalent static loads and default hinges are used for modeling lateral load and force deformation characteristics as a simple approach by the design engineer and this study concludes that this approach leads to severe underestimation of base shear and inaccurate calculation of performance levels. Results also show that NSP analysis overestimates the base shear by 20% and underestimates the roof displacements by 20 to 40%. As regards to the formation trend of plastic hinges, the results of both the analyses shows that the NSP analysis predict severe damage like CP and LS  in some of the frame elements while it shows non-conservative estimate of performance levels in other elements compared to the results obtained from NTH analysis.
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