Probabilistic Seismic Performance Evaluation of Existing RC Frame Structures Retrofitted with Buckling-Restrained Braces

In seismic-prone regions, earthquakes may cause significant damage to existing reinforced concrete (RC) buildings that are not designed to modern standards. This study presents a seismic performance enhancement technique for old buildings using buckling-restrained braces (BRBs). A novel connection is proposed for installing BRBs in existing RC frame structures, termed a cross-orthogonal multidirectional (COMD) connection joint. The main contribution of this study is that the proposed joint makes it possible to avoid drilling holes in the main structural components and ensure the stable cyclic behaviors of BRBs. Furthermore, the Bayesian-based fragility estimation is used to evaluate the effectiveness of seismic upgrading interventions, in which the posterior probability distribution of unknown model parameters is used to quantify their uncertainty. The numerical results indicate that the proposed BRB-to-frame joint ensures effective transfer of loads from the frame to the BRBs. The retrofitting approach can well control the lateral structural displacements. Moreover, the epistemic uncertainty associated with unknown parameters in the demand model has a considerable influence on the seismic fragility estimation. Under the design seismic intensity of 0.2 g , the failure probability of the as-built RC building is about 1.2 under the moderate damage state; conversely, the value is almost 0 for the BRB-retrofitted building. The findings of this study can serve as a reference for improving the seismic performance of existing RC buildings.