Disregarding the Effect of Openings in Infill Walls in Indian Seismic Code: A Scrutiny

Abstract

This study attempts to scrutinize the provision of IS 1893(Part–I): 2016 in neglecting the effect of openings in infill walls in the context of earthquake performance of the same. It evaluates the effect of openings as per FEMA-273 and ATC-40 and compares the result with the provisions of Indian code. The comparative seismic performance, in terms of base shear and top displacement, using the response spectrum of IS 1893(Part–I): 2016, is done on an irregular block of the Jorhat Engineering College old building situated in Seismic Zone-V. Two models of the frame structure are made in SAP 2000®. Modelling of infill is done as Equivalent-Strut, pin-jointed to the RC frame, the width of the strut taking care of effect of openings as per FEMA-273 and ATC-40. The width of the infill wall with openings is found to be 61.465mm whereas, without opening it is 503.80mm. In contrast, as per IS provision the width of infill is 486.27mm. Nonlinear Static Pushover Analysis is performed in SAP 2000®. The building base shear capacity for pushover analysis according to FEMA-273andATC-40 with infill is 10626.107kN and Maximum displacement is 0.042m. In contrast, provisions of IS 1893(part-I):2016 yield the base shear capacity with infill as 20231.365kN and Maximum displacement was 0.063m. An increase in base shear in the latter case may be attributed to the bigger strut width as per IS provision. The formation of plastic hinges is also more in the latter case. It is concluded that IS codal provisions resulted in a doubly stiffer structure.