Strength of circular HSC columns reinforced internally with carbon-fiber-reinforced polymer bars under axial and eccentric loads

So far, limited research has been conducted on high-strength concrete (HSC) columns reinforced with fiber-reinforced polymer (FRP) bars under axial and eccentric compressive loads. The behavior and failure modes of steel-reinforced HSC (steel-RHSC) columns are well known: they fail in compression by concrete crushing and/or in tension (steel yielding). The strength and failure mechanisms of HSC columns reinforced with carbon-FRP (CFRP) bars and spirals has not, however, been investigated yet. This paper presents test results from an experimental program conducted to study the failure mechanism and axial-moment capacity of 10 circular HSC columns reinforced with either CFRP or steel bars and tested under different levels of eccentricity. All the specimens measured 305 mm in diameter and 1500 mm in height. The test variables included different eccentricity-to-diameter ratios and two types of reinforcement (CFRP and steel). Laboratory recorded load-axial displacement, load displacement, failure mode, and reinforcement strain responses of the CFRP-RHSC columns were compared to the steel-RHSC columns. A further analytical study was then conducted based on the test results and plane section theory. Based on this study, the axial and flexural capacity of CFRP-RHSC columns can be accurately predicted using plane sectional analysis. Furthermore, a comprehensive parametric investigation was conducted to generate numerous axial force-flexural moment (P-M) interaction diagrams.