Seismic performance of deficient reinforced concrete frames retrofitted with eccentric steel braces

This research has carried out an experimental study on retrofitting a structure with weak beam-column joints (non-code compliant RC structures). Such structures exhibit poor performance in earthquakes and experience severe damage in the beam/column joint regions. Therefore, a new retrofitting technique is introduced by inserting inverted "V" type of eccentric steel braces to prevent brittle failure at the beam-column joints region. For experimental validation, two 1:3 reduced scaled models were prepared with/without the steel bracings and tested with the help of a seismic simulator (shake table). The 1994 Northridge acceleration time history was selected based on the requirements of regional tectonics. Load and resistant factor design procedures were adopted to design steel braces and connections. The incremental dynamic analysis technique was adopted to determine the maximum roof displacement, peak base acceleration, and base shear force values to determine seismic response and capacity curves. Seismic performance was evaluated on ductility, overstrength, response modification, and yield stiffness. The stiffness of the braced frame was improved by 195% from the as-built frame stiffness, and as a result, the roof displacement was reduced, but story shear capacity was increased from the as-built RC frame. It was observed that no considerable damages appeared after the application of 100% of the acceleration time history. Based on this experimental research, the following results were summarized: the ductility and overstrength factors were evaluated at 2.07 and 5.73, respectively. As a result, the response modification factor was calculated as 11.83, which is 75% more than the response modification factor of the as-built frame. The yield strength of the braced frame was improved by 97%. The performance of the braced frame was found to be better than that of the as-built RC frame.