Abstract
Most existing studies conducted on fiber-reinforced polymer (FRP)-confined concrete have considered circular and square concrete columns, while limited studies have considered columns with rectangular sections. Studies have confirmed that the circular cross-sections exhibited higher confinement effectiveness, whereas in the case of non-circular cross-sections the efficiency of FRP confinement decreases with an increase of the sectional aspect ratio and there is no significant increase, particularly for columns with the aspect ratio of 2.0. As recently suggested by researchers, to significantly increase the effectiveness of FRP-confinement for these columns involves changing a rectangular section into an elliptical or oval section. According to the literature, most of the existing confinement models for FRP-confined concrete under axial compression have been proposed for columns with circular and rectangular cross-sections. However, modeling of the axial strength and strain of concrete confined with FRP in elliptical cross-sections under compression is limited. Therefore, this paper provides new expressions based on limited experimental data available in the literature. For a sufficient amount of FRP-confinement, the threshold value was proposed to be 0.02. Finally, the accuracy of the proposed model was verified by comparing its predictions with the same test database, together with those from the existing models.
Highlights
It is widely reported that confinement of existing concrete columns in bridges and buildings using fiber-reinforced polymers (FRPs) can significantly increase the strength and ductility of the columns
The majority of the existing studies have focused on modeling the stress-strain behavior of FRP-confined concrete in circular cross-sections under axial compression, while only limited studies have considered FRP-confined concrete in rectangular cross-sections [11,12,13,14,15,16,17,18,19,20,21,22]
It has been confirmed by Isleem et al [16,17,18,20,21,22] for rectangular columns of larger-sized cross-sections that the confinement provided by the FRP wraps resulted in a significant improvement in axial strains but only a small improvement in axial strengths
Summary
It is widely reported that confinement of existing concrete columns in bridges and buildings using fiber-reinforced polymers (FRPs) can significantly increase the strength and ductility of the columns. It was concluded that the FRP jackets are not able to effectively improve the compressive behavior of square and rectangular columns exhibiting softening behavior It has been confirmed by Isleem et al [16,17,18,20,21,22] for rectangular columns of larger-sized cross-sections that the confinement provided by the FRP wraps resulted in a significant improvement in axial strains but only a small improvement in axial strengths. The key solution to reduce the corner stress concentration that causes the softening behavior for such large-sized sections and to improve the strength and deformability of concrete columns with light and moderate confinement level is to change the square section into the circular section and the rectangular cross-section into the elliptical or oval cross-section by subsequent steel or composite jacketing [30,31,32,33,34,35]. Good agreement was shown between the predictions of the model and the results, confirming that the model is able to reproduce the results of columns with elliptical FRP-jackets
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