Seismic Retrofit of Vulnerable Steel Frames Using Articulated Quadrilateral bracing system

This paper investigates the applicabilty of an innovative bracing, called Articulated Quadrilateral (AQ) bracing system, which uses shape memory alloys (SMAs), for retroffiting low-rise to high-rise vulnerable SMFRs against strong ground motions. The paper investigates brace fundamental engineering characteristics, design of the system and also configuration of the brace (the proportion of SMA wire, C-shape dissipator and Post-tensioning tendons). OpenSees program is utilized for nonlinear dynamic finite element analysis and the validation of modeling using data from full-scale experimental tests performed by Speicher et al. at Georgia Institute of technology. Using 3-, 9- and 20-story steel moment resisting frames from the SAC phase II project, nonlinear pushover, incremental dynamic analysis, and fragility analysis of frames with and without AQ bracing were conducted using FEMA P695 far-field ground acceleration records. Results show that by retrofitting MRF system with AQ bracing, strength of the buildings increases up to 40%. Also, bracing of the frames yields more uniform drift distribution which reduces the likelihood of soft story formation.