EXPERIMENTAL STUDY ON BUCKLING RESTRAINED BRACES WITH POST-TENSIONED CARBON FIBER COMPOSITE CABLES

Seismic performance of buildings is generally evaluated by peak values of drift/displacement response to assure life safety performance level. Residual deformation following a strong earthquake is a significant indicator to make a decision whether existing buildings could be operational or not. Final condition of structures with higher importance factors such as hospitals, schools, bridges etc. is expected to be operational after a design basis earthquake (DBE). Previous researchers showed that post-yield stiffness for bilinear hysteretic behavior or post-tensioning force for flag shaped hysteretic behavior are highly effective in reducing such residual deformations. Also, fully self-centering behavior may be not necessary in most cases since negligible residual deformation can be accepted. This study aims to present a new brace which consists of buckling restrained brace as energy dissipator and carbon fiber composite cables (CFCCs) for providing additional post-yield stiffness and self-centering force. Loss of post-tensioning force and change in stiffness are investigated experimentally for CFCC coupons. Three BRBs with post-tensioned carbon fiber composite cables (PT-BRB) are designed for this experimental study. One of the PT-BRBs is designed to have bilinear behavior with relatively high post-yield stiffness while the other two specimens use partially self-centering BRBs with different levels of post-tensioning force. A numerical study is further conducted to compare with the experimental results. Special emphasis is given on the impact of post-tensioning force. The experimental study shows that CFCCs achieve to increase post-yield stiffness of the buckling restrained braces developed herein. A stable partially self-centering behavior is possible as well.