Simplified relations for confinement factors of partially and highly confined areas of concrete in partially encased composite columns

In this paper, the new analytical expressions of confinement factors for partially and highly confined areas of partially encased composite (PEC) columns fabricated by thin-walled cross- and H-shaped structural steel sections are proposed. A three-dimensional (3D) nonlinear finite element analysis based on the dynamic explicit method was performed to predict the load-displacement relationship of the PEC columns using the proposed confinement factors. The model was verified against experimental results from the literature, which indicated that load bearing capacity and load-displacement behavior of PEC columns can be estimated accurately. A parametric study was performed based on numerical model to investigate the influence of the compressive strength of concrete, transverse link spacing, and structural steel shape on axial behavior of the PEC columns. The findings demonstrate that the partially and highly confined area is greatly influenced by the shape of steel section. As consequence of improvement in behavior, the usage of cross-shaped section possesses greater highly confined area which the maximum coefficients of partially and highly confined areas are 1.55 and 2.01, respectively. The comparison of proposed model and squash load against test results shows that analytical generated expressions are advisable to be used for design purposes.