Torsional Behavior of Reinforced Concrete Members Wrapped with CFRP Sheets

Abstract

This paper presents the torsional behavior of reinforced concrete (RC) members fully wrapped with carbon fiber-reinforced polymer (CFRP) sheets. A total of twelve rectangular RC specimens of identical cross sections were tested under pure torsion (beams) or combined axial compression and torsion (columns). In the case of column specimens, an axial force simulating the service loads was applied before CFRP strengthening and maintained constant during the static test under torsion. The magnitude of axial force was 25% of the nominal compressive strength. Therefore, test variables included the presence of axial force (beam or column), stirrup spacing (75 or 150 mm), hook angle (90 or 135°) of the closed stirrups, and presence of CFRP sheets. Test results showed that the externally bonded CFRP sheets significantly increased the cracking, yielding, and maximum torsional moment capacities of RC beams and columns. The full wrap configuration enhanced the maximum torsional moment capacity by up to 190% and 116% for RC beams and columns, respectively. Also, the use of 135-degree hook for closed-stirrups was more effective than 90-degree hook for both unwrapped and CFRP-wrapped members. Finally, the effective CFRP strain equation by fib14 correlated better with RC beams than columns.