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Performance based seismic evaluation beyond Immediate occupancy level of existing rc structures Using control and strengthening techniques

Milan Nakum and G Rami Reddy

Paper No.: 576

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Vol.: 60

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No.: 1

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March, 2023

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pp. 1-25

Abstract

 

Structures are commonly subjected to normal loads as well as accidental loads caused by earthquakes. According to the standards, structures are designed employing a force-based method. The provisions in the code are meant to prevent collapse during earthquakes, and the performance of a structure is evaluated qualitatively. This Paper aims to understand that the performance of existing structures against seismic loads can be improved by adopting the Performance Based Seismic Design (PBSD) approach. Performance based design helps in achieving the targeted performance level of a structure like Operational (O), Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP). The use of Strengthening methods or Response control methods of retrofitting can provide better performance for existing structures subjected to earthquakes. Earlier researchers have performed retrofitting using a combination of Friction damper and steel bracing of Reinforced Concrete (RC) buildings and achieved the IO performance level. If performance levels are beyond IO, structural elements and components will see nonlinear deformations causing energy dissipation. If control methods and strengthening methods are used to improve the performance of the existing RC structure, the effect of energy dissipation in the elements and components needs to be considered while evaluating the responses. This aspect was not considered earlier and proposed to be investigated in the present work. The 5-story RC building is considered and is retrofitted with a Friction damper and steel bracings in the present work to achieve the desired performance beyond the IO level. Pushover analysis is performed with the help of SAP2000 (2021) to determine the structure’s realistic capacity and element energy dissipation based on the user-defined hinge characteristics and the Time history analysis is performed to get the energy dissipation from dampers. The methodology of retrofitting to reach the desired performance level is provided and a comparison of results before and after retrofitting of the structure is made.
Keywords: capacity, demand; earthquake; hinge; performance based seismic design; Performance level; retrofitting; seismic evaluation

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