Recent devastating earthquakes around the world have shown the vulnerability and deficiencies of existing reinforced concrete (RC) frame structures.In particular, recent research on seismic risk analysis have highlighted that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames.Therefore, for this type of structures, it is necessary to accurately model materials and members to capture the flexure, shear and flexure-shear failure modes in members and the potential collapse of the structure.In this paper, alternative retrofit methods are evaluated for these older frame buildings using a nonlinear structural performance assessment methodology.As a case study, the longitudinal frame of an existing building is modeled, including the effect of flexural-shearaxial load interaction and the bar slip deformational component in order to be able to capture column shear and axial failures.A probability-based framework is implemented in order to assess the structural performance and safety at each chosen performance level.This study shows that it is crucial to choose the most effective retrofit strategy based on the assessed performance of the bare frame.
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