Nonlinear finite element analysis of reinforced concrete columns: Evaluation of different modeling approaches for considering stirrup confinement effects

Abstract

The present study aimed to introduce an accurate modeling strategy for the three‐dimensional (3D) nonlinear finite element analysis of reinforced concrete (RC) columns considering the effects of the stirrup confinement. For this purpose, concrete columns with different geometric characteristics and various reinforcement details whose experimental test data are available, were analyzed using the finite element method. The concrete damaged plasticity (CDP) was used to model the nonlinear behavior of the concrete material in the compression and the tension. The ideal elastic–plastic constitutive law was utilized for modeling the behavior of longitudinal and transverse rebars. Through comparing the experimental data and numerical results, the effect of various parameters, such as the type of stress–strain relationships used for modeling the behavior of confined concrete and the type of element used to model the stirrups, were evaluated. Additionally, the sensitivity of numerical results against the CDP model parameters (i.e., the viscosity parameter, the flow potential eccentricity, the dilation angle, the ratio of biaxial compressive strength to its uniaxial compressive strength, and the ratio of the second stress invariant on the tensile meridian) were investigated. The results show that the presence and modeling of stirrups in the RC columns alone are not enough for capturing the effects of concrete confinement. The use of beam elements instead of truss elements for modeling the stirrups as well as the use of Vallenas stress–strain relations for modeling the uniaxial behavior confined concrete, leads to numerical results that are more close to the experimental data.

Numerical evaluation of axial compressive behavior of hollow concrete columns reinforced with GFRP bars and spirals

“…For the eccentricity (ϵ), ratio of the compressive strength under biaxial loading to uniaxial (f b0 =f c0 ), and the shape factor (K c ) the default values, 0.1, 1.16, and 0.667, respectively, as selected by past researchers were considered. [49][50][51][52][53][54] In CDP model, the compressive behavior of concrete can be defined in tabulated form. It consists of stress (σ c ), inelastic strain (ε in c ) corresponding to stress value, and damage parameter (d c ).…”

“…Many researchers have successfully employed simple "embedded region constraint" to define the interaction between concrete and reinforcing bars, especially for concentrically loaded specimens under compression. 52,[62][63][64] The embedded region constraint considers the ideal bond between concrete and reinforcement without any slip. This ideal bond assumption does not affect the results for concentrically loaded columns as the strain in concrete and reinforcing bars is comparable.…”

“…In the selection of element types, for concrete columns with spiral reinforcement, concrete as well as FRP reinforcement are assigned C3D8R "an 8-node linear brick, reduced integration, hourglass control". 50,52,[65][66][67][68][69][70]…”

“…When and , the model predicted the behavior with good accuracy and reasonable computation time. For the eccentricity (), ratio of the compressive strength under biaxial loading to uniaxial (), and the shape factor ( K c ) the default values, 0.1, 1.16, and 0.667, respectively, as selected by past researchers were considered 49–54 …”

“…The interaction between concrete and FRP reinforcement can be achieved through surface‐to‐surface contact, but it is complicated and increases the complexity of the numerical model. Many researchers have successfully employed simple “embedded region constraint” to define the interaction between concrete and reinforcing bars, especially for concentrically loaded specimens under compression 52,62–64 . The embedded region constraint considers the ideal bond between concrete and reinforcement without any slip.…”