| Abstract: |
Aging reinforced concrete (RC) multi-storey infrastructure across high-seismic zones in India exhibits severe vulnerability under revised seismic demand criteria established by IS 1893 (Part 1):2016. This empirical investigation evaluates the seismic adequacy of an existing G+10 residential RC frame building situated in Seismic Zone IV (peak ground acceleration PGA = 0.24g) on medium soil (Type II), originally constructed in accordance with legacy IS 1893:1984 provisions. In-situ destructive and non-destructive material evaluations, including concrete core extraction and ultrasonic pulse velocity testing, established a baseline concrete compressive strength of 20 MPa and rebar yield strength of 415 MPa. Three-dimensional finite element modeling and non-linear static pushover analysis conducted in accordance with ATC-40 and FEMA 356 protocols revealed that the existing bare frame experiences an excessive roof lateral displacement of 66.8 mm and a maximum inter-storey drift ratio of 0.54%, directly violating the codal limit of 0.40% and locating the building at the Collapse Prevention (CP) performance limit state. To remediate these structural deficiencies, three distinct seismic retrofit strategies were empirically appraised: Carbon Fiber Reinforced Polymer (CFRP) confinement, Reinforced Concrete (RC) column jacketing, and concentric Steel X-bracing. Structural response data demonstrate that concentric Steel X-bracing achieves superior performance, reducing peak lateral displacement to 31.2 mm (a 53.3% reduction) and maximum drift to 0.21%, while elevating the base shear capacity by 97.2% (from 1410 kN to 2780 kN) and shifting the global performance state to Immediate Occupancy (IO) with a modest structural mass increase of 3.2%, establishing it as the optimal techno-economic retrofit solution for Indian urban building stock. |
