FRP-Confined Square Concrete Columns with Section Curvilinearization under Axial Compression

Existing studies have shown that fiber-reinforced polymer (FRP) jacketing/wrapping is highly effective in strengthening circular concrete columns but is much less effective for rectangular/square concrete columns due to the existence of flat sides and sharp corners in the latter. Rounding the corners can enhance the effectiveness of FRP confinement, but its benefit is limited, particularly for large-scale columns, because the corner radius is limited by the presence of internal steel reinforcement. An alternative strengthening technique therefore has been proposed by some researchers, in which the flat sides of a rectangular/square section are modified into slightly curved sides (i.e., curvilinearization) before FRP jacketing/wrapping. This section curvilinearization (SC) method increases the section size by only a limited extent but can substantially enhance the effectiveness of FRP confinement for rectangular/square columns. However, only very limited research has been conducted on curvilinearized rectangular/square columns (CRCs or CSCs), and the few existing studies are limited in scope and were conducted using small specimens. This paper presents the results of a systematic experimental program on the behavior of CSCs, in which 16 small-scale and 10 large-scale FRP-confined square concrete columns with or without section curvilinearization were tested under axial compression. A comparison of the results for columns of the two different sizes indicates that the size effect is very limited in these FRP-confined CSCs. The accuracy of two existing stress-strain models for FRP-confined concrete in CRCs was evaluated using the test results, revealing the need for the development of an improved stress-strain model for use in design.