Analytical seismic assessment for reinforced concrete moment frame residential buildings constructed in the Soviet Union Era in Almaty, Kazakhstan

Abstract

In Almaty, the largest city in Kazakhstan lying on a high seismic region, many residential buildings constructed during the Soviet Union are still in service. These buildings were not properly designed against earthquakes and special seismic detailing was not well considered according to the local design code. Therefore, this paper presents an analytical seismic assessment of two typical reinforced concrete moment frame residential structures constructed in this era, representing 812 buildings with almost identical construction materials, geometries, and structural details. Two-dimensional nonlinear models were developed for these buildings in each orthogonal direction based on the structural details collected from a Kazakh government agency. Incremental dynamic analyses were then performed using 24 historical strong ground motions with fault characteristics similar to those in the Almaty region. Structural global and local seismic responses were investigated. A new approach was proposed to define structural global inter-story drift limits at different damage states based on local seismic demands considering uncertainties of earthquakes and structural nonlinear dynamic responses. Based on these inter-story drift limits, the structural fragility curves were then developed to identify the damage probability of these buildings, which were further used to roughly estimate repair costs at different earthquake intensity levels. It has been found that these buildings are vulnerable to destructive earthquakes due to poor structural details. They possess a high probability of incurring extensive damage (high repair cost) or even collapsing (irreparable) at the earthquake intensity level, with a return period of 475 years or 2475 years, respectively.