SEISMIC EVALUTION OF REINFORCED CONCRETE FRAMED STRUCTURES

Abstract

In last decade, Bhuj earthquake of 2001 raised the questions about the adequacy of framed structures to resist strong seismic motions. Under such circumstances, to evaluate the performance of reinforced concrete (RC) framed buildings for future expected earthquakes, a non-linear static (pushover) analysis can be conducted. Pushover analysis evaluates the performance level of the building components and maximum base shear carrying capacity of the structure for various zones. This analysis is carried out for hinge properties, available in programs based on the FEMA-356 and ATC-40 guidelines. Prediction of non-linear parameters of shear hinge in RC members is difficult because it involves a number of parameters like shear capacity, shear displacement, and shear stiffness. As shear failure is brittle in nature, designer must ensure that flexural failure (ductile mode of failure) precedes the shear failure. However, past earthquakes reveal that majority of the RC framed structures failed due to shear. Therefore, accurate modelling of shear failure is almost certain for seismic evaluation of RC framed building. The current industry practice is to do non-linear static (pushover) analysis for flexure only. To demonstrate the importance of modelling shear hinges a RC framed building, G+4 in zone-IV is selected. Two building models, one with shear hinge and other without shear hinges, are analysed using non-linear static (pushover) analysis. This study found that modelling shear hinges is necessary to correctly evaluate strength and ductility of the building. When analysis ignores shear failure model it overestimates the base shear and roof displacement capacity of the building. The results obtained here show that the presence of shear hinge can correctly reveal the non-ductile failure mode of the building. Therefore, the primary objective of the present work is to demonstrate the importance of modelling shear hinge in seismic evaluation of RC framed building.