Seismic Strengthening of a Deficient Pre-Code G+4 RC Frame by Concrete Column Jacketing: An ETABS Evaluation under IS 1893:2016

Abstract

A large fraction of India's residential reinforced concrete (RC) building stock was constructed before modern seismic provisions, leaving frames structurally deficient under current codes. This study evaluates concrete column jacketing as a practical retrofit technique for a representative deficient G+4 RC frame located in Pune, Maharashtra. The building has a 20 m x 12 m plan, a total height of 15.5 m, and 300 mm x 300 mm external columns typical of pre-code construction. The original frame was modelled in ETABS v23.2.0 and analysed as an ordinary moment-resisting frame (OMRF, R = 3.0) under IS 1893 (Part 1):2016 equivalent-static seismic loading for Zone III, Soil Type II (Z = 0.16). The original frame violates the IS 1893:2016 inter-storey drift limit of 0.004h at four of five storeys in both principal directions, reaching maximum drift ratios of 0.006474 (X) and 0.005963 (Y), approximately 1.6 times the permissible value. A 75 mm M30 reinforced-concrete jacket was then applied to all columns, enlarging external columns from 300 x 300 mm to 450 x 450 mm, and the strengthened building was re-analysed as a special moment-resisting frame (SMRF, R = 5.0). Post-jacketing, maximum drift fell to 0.002931 (X) and 0.003086 (Y), reductions of 54.7% and 48.2% respectively, achieving full code compliance at every storey. The fundamental period reduced from 0.717 s to 0.613 s, and the dead load increased by only 6.9%. Concrete column jacketing is an effective, practical intervention for restoring seismic code compliance in pre-code Indian RC frames.