Structural assessment and retrofitting of an old building in highly seismic zone of Pakistan

Abstract

This study evaluates the seismic performance of a 40-year-old, four-story reinforced concrete building in Abbottabad, Pakistan, a highly seismic region. The structure, designed without adherence to current seismic provisions outlined in the Building Code of Pakistan 2021, was analyzed using a displacement-based approach (nonlinear static analysis) and incremental dynamic analysis (nonlinear dynamic analysis). The static analysis revealed that the building met performance objectives but exhibited low base shear and stiffness in its longer (x) direction, leading to significant member-level damage. Dynamic analysis further highlighted excessive drift and displacement in the x-direction, attributed to the building’s stiff-weak configuration, with excessive stiffness in the shorter (y) direction to support gravity loads and insufficient strength in the x-direction. To mitigate these vulnerabilities, shear walls were analytically introduced in the x-direction, effectively controlling displacement and reducing damage. The findings underscore the need for retrofitting older structures to enhance seismic resilience in high-risk regions.