Compressive behavior of large rupture strain (LRS) FRP-confined square concrete columns: experimental study and model ev
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ORIGINAL ARTICLE
Compressive behavior of large rupture strain (LRS) FRPconfined square concrete columns: experimental study and model evaluation Qiang Han . Wanying Yuan . Yulei Bai . Xiuli Du
Received: 1 April 2020 / Accepted: 13 July 2020 Ó RILEM 2020
Abstract A large rupture strain (LRS) fiber reinforced polymer (FRP), with a rupture strain value of more than 5%, is a promising alternative to traditional FRPs with a 1–3% rupture strain for seismic retrofitting of reinforced concrete (RC) structures. The LRS FRPs provide a bilinear stiffness around concrete columns while this feature is linear for traditional FRPs (e.g., carbon FRP). This paper presents a careful analysis of the compressive behavior of LRS FRP wrapped square column, especially since their confining stress is nonuniformly distributed. A total of 66 square concrete columns, measuring 150 9 150 9 300 mm with varied corner radii from 0 to 75 mm were tested under monotonic axial compression. The experimental results, in terms of full stress–strain behavior, compressive strength, hoop strain distribution, and dilation behavior were systematically investigated. As the corner radius increases, the strength enhancement after LRS FRP confinement
Q. Han W. Yuan Y. Bai (&) X. Du Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing, China e-mail: [email protected] Q. Han e-mail: [email protected] W. Yuan e-mail: [email protected] X. Du e-mail: [email protected]
also increases, and the hoop strain is more uniformly distributed. The stress–train curves exhibit a triplesection pattern with a smooth transition zone. The peak dilation rate of LRS FRP-confined concrete is higher than that of traditional FRP-confined concrete, and the curve of dilation rate versus axial strain exhibits a remarkably long stable response. Moreover, results show that most existing models of FRPconfined concrete can provide conservative predictions for an improved compressive strength of LRS FRP-confined square concrete columns. Keywords Fiber reinforced polymer (FRP) Large rupture strain (LRS) Confinement Square column Compressive behavior
1 Introduction With the excellent characteristics of fiber reinforced polymer (FRP) composites (e.g., high strength/weight ratio, flexibility of shape), many studies have been published on the compressive behavior of FRPconfined circular and noncircular (i.e., square or rectangular) concrete columns and extensive confinement models have been proposed [1–14]. For FRPconfined circular columns, the strength and ductility of the column are significantly improved due to the uniform confinement along the perimeter. Conversely, in noncircular columns, the confining pressure is high
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at the corners and low along the middle sides; thus, only part of the concrete is effectively confined. Consequently, the strength gain of a square column is lower than that of a circular column under the same
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