Cyclic stress-strain model incorporating buckling effect for steel reinforcing bars embedded in FRP-confined concrete

• Published in: Composite structures 2017-12, Vol.182, p.54-66
• Main Authors: Bai, Yu-Lei, Dai, Jian-Guo, Ozbakkaloglu, Togay
• Format: Article
• Language: English
• Subjects: Bar buckling; Cyclic model; FRP confinement; OpenSees; Stress-strain model
• ISSN: 0263-8223; 1879-1085
• DOI: 10.1016/j.compstruct.2017.09.007

Buckling of steel reinforcement usually causes a sudden loss of the load-carrying capacity and the ultimate state of conventional reinforced concrete (RC) cylinders. However, reinforcing bars behave differently in fiber-reinforced polymer (FRP)-confined RC cylinders due to the lateral confinement effect of FRP. This paper presents a theoretical study into the buckling behavior of longitudinal steel reinforcing bars embedded in FRP-confined concrete subjected to cyclic axial compression. An empirical monotonic compressive stress-strain model considering the buckling effects proposed previously for laterally supported reinforcing bars is extended to a cyclic model by combining the monotonic envelope and the Menegotto-Pinto model accounting for the cyclic loops. The cyclic stress-strain models for both laterally supported reinforcing bars and FRP-confined plain concrete are then implemented into the OpenSees software platform and validated through comparisons with compressive test results on cyclically loaded FRP-confined plain and RC cylinders. The proposed cyclic stress-strain model for laterally supported reinforcing bars is expected to serve as a fundamental model for predicting the seismic behavior of FRP-strengthened RC cylinders with widely-spaced transverse ties under cyclic axial compression, in which case the local buckling of reinforcing bars usually occurs between two adjacent transverse ties.