A Plasticity Model For Confined Concrete Including Creep Effects

The structural analysis under in-service conditions requires a reliable constitutive model which takes into account the effects of sustained service loading which results in creep deformations and processes ac-companying creep like hardening and damage. The research’s purpose is to present a material model which can accurately predict the ultimate stress-strain response of confined concrete previously subjected to a sustained service load.An experimental program including two stages was conducted to examine the effects of sustained service loading on the axial behavior of FRP confined concrete. At the first stage, the creep strain of FRP confined concrete under uniaxial compression loading was examined. Then at the second stage, after the sustained load was removed, the specimens were loaded to failure to obtain the stress strain curves. The results of the experimental program indicate that the presence of a sustained service load changes the expected failure mode from FRP rupture to FRP de-lamination and the difference of the stress-strain response is approximately10%between the creep specimen and the companion one. Specially, the sustained loading increases the elastic modulus, slightly decreases the compressive strength, and degrades the deformation capabilityBased the microprestress solidification theory, a creep model for FRP confined concrete is developed, in which effects of fly ash and varying stress are taken into account. By treating an irrecoverable or residual strain as the initial value of the plastic strain parameter, a plasticitiry model is modified to reproduce the behavior of confined concrete after creep process. The proposed stress-strain model is shown to accurately describe the compressive behavior of confined concrete of this research and can improve the design and rehabilitation of structures so that they meet safety requirements in future service life.