Numerical modeling of circular, square and rectangular concrete columns wrapped with FRP under concentric and eccentric load

Abstract

In this paper, the finite element method was used for the numerical modeling of columns with square, rectangular and circular cross sections wrapped with FRP. The numerical modeling was successfully calibrated with the experimental data considering axial load, axial strain and transverse strain. The distribution of compressive stresses in the cross section of the column indicates that for centered load, circular cross sections have uniform distribution and for square and rectangular sections the effective confined concrete was defined by parabolas and concentrates next to the rounded corners. For eccentric load, the effective confined region moves to the most confined edge, thus, this does not reduce the gain for square and rectangular columns, but is unfavorable for circular columns.

Unified model for fully and partially FRP confined circular and square concrete columns subjected to axial compression

“…( 20), k h,eff is a function of D I eq and D II eq , strongly depending on R b . For the case of FFSC with relatively sharp corner (R b ≃ 0), Area I would become virtually marginal as numerically confirmed by [30][31][32][33]. Consequently, for R b ≃ 0, by ignoring the contribution of (f I l,f ) acting on Area I in terms of f l,eff (D I eq ≃ 0), the entire effective confinement area (with D eq,c ) can be assumed to be only under f II l,f , leading to D II eq ≃ D eq,c .…”

“…is in a direct proportion with FRP confining stress f * f generated in the perimeter of the equivalent circular cross-section. Nonetheless, as experimentally confirmed by Ozbakkaloglu [6], Chen and Ozbakkaloglu [7], Shan et al [19] and Oliveira and Carrazedo [33], for a square section, at a certain axial strain (ε c ), the middle of the flat side would experience the maximum hoop strain in the perimeter (ε h,max = ε h,m ), but the minimum occurs at the corners (ε h,min = ε h,c ) as demonstrated in Fig. 4e.…”

“…where n f is the number of FRP layers; t f is the thickness of a FRP layer; E f is the FRP modulus of elasticity. Nevertheless, contrary to OCCEF, the finite element simulations performed by [30][31][32][33] well evidenced that the effective confined area is subjected to a non-uniform distribution of confinement pressure, which strongly depends on the dimension of the corner radius (R b ). Fig.…”

“…The former is assumed to be homogenously/effectively mobilized by confinement pressure, while the latter is assumed to be as unconfined concrete. However, the finite element simulations performed by [30][31][32][33] demonstrated that the effective confinement area is subjected to a non-uniform distribution of confinement pressure, which strongly depends on the length of corner radius. Furthermore, the studies [6,7,32,33] experimentally evidenced that FRP hoop strain at the horizontal direction is non-homogenously distributed in the perimeter, in contrary to what happens in circular sections.…”

“…However, the finite element simulations performed by [30][31][32][33] demonstrated that the effective confinement area is subjected to a non-uniform distribution of confinement pressure, which strongly depends on the length of corner radius. Furthermore, the studies [6,7,32,33] experimentally evidenced that FRP hoop strain at the horizontal direction is non-homogenously distributed in the perimeter, in contrary to what happens in circular sections. On the other hand, for the establishment of axial stress-strain response of FPCC, the concept of confinement efficiency factor is also adopted by addressing the effect of vertical arching action (and horizontal arching action effect in case of FPSC) in the determination of confinement pressure imposed by FRP strips.…”