Performance Based Seismic Assessment of Regular and Irregular Tube-in-Tube RC Structures Using Pushover Analysis

Seismic activity remains a critical concern in the design of high-rise buildings due to their height and flexibility, which amplify lateral responses during earthquakes. Among various structural systems, the tube-in-tube configuration offers enhanced lateral stiffness and energy dissipation capacity, making it a widely adopted solution for tall structures in seismic regions. This study evaluates the seismic performance of reinforced concrete tube-in-tube buildings using nonlinear static pushover analysis. Three building heights G+29, G+39, and G+49 stories were analyzed under seismic zones 2, 4 and 5B based on the Egyptian Code (ECP-201) for loading and the ATC-40 guidelines for performance evaluation. Both regular and vertically irregular configurations were modeled using SeismoStruct software. The analysis applied the Displacement Coefficient Method (DCM) to estimate inelastic demands, assessing inter-story drift ratios, target displacements, and plastic hinge distributions. The results revealed that geometric irregularities significantly increase lateral displacements and hinge concentration, especially in higher seismic zones. Performance levels were evaluated using plastic hinge criteria and pushover curves. Retrofitting strategies mainly stiffness enhancement proved effective in reducing target displacements and improving performance classification. The findings emphasize the impact of structural configuration and highlight the role of performance-based seismic design in enhancing the resilience of high-rise buildings.