Capabilities of existing frame buildings with shear diaphragms to resist seismic effects of destructive earthquakes

In recent times, numerous powerful earthquakes have struck across the globe, with intensities exceeding standard design values by 1 … 2 points, resulting in widespread destruction of buildings and infrastructure. These events underscore the urgent need to revise current regulatory frameworks, particularly by increasing the prescribed seismic design loads. Consequently, it becomes essential to reassess the seismic performance of existing buildings that were originally designed according to outdated codes. This article explores the critical issue of evaluating and enhancing the earthquake resilience of such structures in light of evolving seismic realities.This article presents the results of a seismic resistance assessment for a nine-story reinforced concrete frame building with stiffening diaphragms, subjected to seismic loads exceeding the original design values. To evaluate the seismic performance of the existing structure, a numerical analysis was carried out using a static nonlinear (pushover) method. As a failure criterion, the maximum seismic load corresponding to the complete loss of the building’s load-bearing capacity was selected. The seismic resistance was assessed by considering the maximum values of seismic impact from two horizontal components, applied independently along each principal direction of the building. According to the adopted methodology, the structural model of the building frame, subjected to vertical loads, was incrementally loaded with the horizontal component of seismic action using displacement-controlled nonlinear static analysis. The horizontal load was gradually increased until the structure reached its maximum seismic capacity. The building under study was originally designed in accordance with the outdated seismic code SNiP RK 2.03-30-2006, which specified a seismic load corresponding to a site acceleration of 0.125g. However, under current seismic design standards—SP RK 2.03-30-2017*—the same site is classified for a seismic acceleration of 0.2g. Therefore, the existing structure is now expected to resist a seismic load that is 1.6 times greater than the load considered in its original design (0.2g vs. 0.125g). The study revealed that complete loss of the building's load-bearing capacity occurs under a special load combination when the seismic load is applied in the direction of the Y-axis. It was determined that structural failure takes place at the thirteenth loading stage, corresponding to a horizontal seismic acceleration of 0.163g. This value is lower than the required acceleration of 0.2g as specified by the current seismic code SP RK 2.03-30-2017*. This finding indicates that the building is incapable of withstanding the seismic demands outlined in the updated standards, highlighting its insufficient seismic resistance under the revised design requirements. Based on the results of the conducted research, it was proposed to strengthen the structural system of the building, which was originally designed and constructed in accordance with the outdated standards SNiP RK 2.03-30-2006, in order to enhance its seismic resistance and ensure compliance with current seismic safety requirements.