Abstract
The majority of experimental and analytical studies on fiber-reinforced polymer (FRP) confined concrete has largely concentrated on plain (unreinforced) small-scale concrete columns, on which the efficiency of strengthening is much higher compared with large-scale columns. Although reinforced concrete (RC) columns subjected to combined axial compression and flexural loads (i.e., eccentric compression) are the most common structural elements used in practice, research on eccentrically-loaded FRP-confined rectangular RC columns has been much more limited. More specifically, the limited research has generally been concerned with small-scale RC columns, and hence, the proposed eccentric-loading stress-strain models were mainly based on the existing concentric-loading models of FRP-confined concrete columns of small scale. In the light of such demand to date, this paper is aimed at developing a mathematical model to better predict the strength of FRP-confined rectangular RC columns. The strain distribution of FRP around the circumference of the rectangular sections was investigated to propose equations for the actual rupture strain of FRP wrapped in the horizontal and vertical directions. The model was accomplished using 230 results of 155 tested specimens compiled from 19 studies available in the technical literature. The test database covers an unconfined concrete strength ranging between 9.9 and 73.1 MPa, and section’s dimension ranging from 100–300 mm and 125–435 mm for the short and long sides, respectively. Other test parameters, such as aspect ratio, corner radius, internal hoop steel reinforcement, FRP wrapping layout, and number of FRP wraps were all considered in the model. The performance of the model shows a very good correlation with the test results.
Highlights
The application of fiber-reinforced polymers (FRPs) has been abundantly used to retrofit concrete columns in existing buildings and bridges. The importance of this subject has been confirmed by numerous researchers and their studies reported that the axial compression strength and ductility of concrete columns under pure concentric loading can be substantially increased using the FRP wrapping system (e.g., [1,2,3,4,5])
It is assumed in the current model that the FRP rupture strain is dependent on the side length and on the ratio of the corner radius, which could be 2rc /h or 2rc /b as used for FRP-confined rectangular sections tested by Isleem et al [12,13,14]
The database covers a wide range of test variables such as cross-sectional size, aspect ratio, corner radius, and ratio of internal hoop steel reinforcement, FRP wrapping scheme, and amount of FRP
Summary
Yang et al [22] studied the structural performance of eccentrically loaded columns through tests on CFRP-strengthened high strength concrete columns with a rectangular cross section of 150 mm × 200 mm and a height of 1200 mm. There are only very few studies available on concentricallyloaded FRP-confined RC columns that address the strength enhancement caused by the confinement from using external FRP confinement and internal steel confinement (e.g., [10,11,12,13,14,23,24,25,26]) Of these studies, a series of 68 axial compressive tests on FRP-wrapped reinforced concrete in 150 mm × 300 mm rectangular-sectioned and 250 mm × 250 mm square and circular-sectioned columns of 500 mm in height were conducted by Ilki et al [24].
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