SLaMA-Based Retrofit of RC Frame Buildings Using Alternative Bracing Systems

Abstract

This paper introduces a retrofit design procedure for reinforced concrete (RC) frame buildings using alternative steel bracing systems based on the simple lateral mechanism analysis (SLaMA). Employing a displacement-based design approach, the procedure captures the actual behavior of existing buildings and the contribution of the bracing system. The retrofit design process and seismic assessment procedures are outlined, followed by the proposed SLaMA-based retrofit design procedure. The design procedure is demonstrated on pre-1970 four-story and eight-story RC case study frames, targeting maximum displacements informed by the expected failure mechanisms identified using a detailed seismic assessment (DSA). The New Zealand Society of Earthquake Engineering 2016/017 Seismic Assessment Guidelines’ SLaMA method is utilized for DSA, revealing that the frames are potentially earthquake-prone with specific failure mechanisms and seismic capacities. After retrofitting with a concentric braced frame (CBF), buckling-restrained brace (BRB), and CBF with friction dampers, the failure mechanisms are modified, resulting in seismic capacities exceeding 100% New Building Standard (NBS). Evaluation of local and global behavior post-retrofit enables the determination of the advantages and disadvantages of alternative brace systems. Nonlinear time-history (NLTH) analyses using a lumped plasticity model verify the results, affirming the viability and practicality of the SLaMA-based retrofit design procedure for selecting and designing appropriate interventions in concrete frame buildings.