Cyclic test and finite element analysis of a steel double K-braced frame with laterally-restrained plates for RC building retrofit

Abstract

Damage was discovered in existing 24-story reinforced concrete (RC) buildings in New Taipei City under the 2015 Hualien earthquake with a magnitude of 6.3. A new scheme was proposed to retrofit the buildings by adding a steel concentrically double K-braced frame in a limited space, with diaphragm plates to laterally restrain each brace to increase its buckling strength. A cyclic test was first conducted on a full-scale steel braced frame specimen, composed of a steel boundary frame, two pairs of K-type-arranged plates for axially loaded braces, diaphragm plates for brace buckling restraint, and surrounding RC members. Secondly, a finite element (FE) analysis was conducted on the specimen for a correlation study and investigation of force transfer between the infilled braced frame and surrounding RC members. A finite element parametric study was then conducted on single braces with different numbers of restraint and plate thicknesses to investigate the cyclic behavior and buckling force. The AISC 360-16 (2016) provides a very conservative prediction of the brace bucking force, but the prediction based on Wolchuk (1963) reasonably matches well the test and FE analysis results. A cyclic backbone curve for a single brace modeling, considering in-plane lateral supports, was proposed in this work.