Modeling for complete stress-strain curve of circular concrete columns confined with steel spiral and FRP

The results of 153 specimens from an experimental study on fiber-reinforced polymer (FRP) and steel spiral-confined (FRP-SS-confined) circular concrete columns were collected from accessible literature to establish a database. The existing models of FRP-SS-confined circular concrete columns were included and evaluated. A new stress-strain model with a simple, continuous, general expression was put forward for FRP-SS-confined circular concrete columns by taking into account various confining conditions during the loading process. Calculation models of the ultimate stress, ultimate strain, peak stress and peak strain were proposed by considering the contributions from both steel spiral confinement and FRP confinement. The comparison showed that the elastic stage, nonlinear transition stage, linear hardening stage and residual stage of the stress-strain curves were well captured by the proposed model for FRP-SS-confined circular concrete columns. Compared with other existing models, the proposed model showed better flexibility and versatility for practical application. In particular, various declining trends in the residual stages corresponding to the different confining conditions were well predicted by the proposed model. Furthermore, the effects of different parameters (steel tube thickness, FRP type, FRP layer and unconfined concrete strength) on the behavior of FRP-SS-confined circular concrete were discussed. •Existing stress-strain models of concrete confined with steel spiral and FRP were investigated.•153 data samples of FRP-SS-confined concrete columns were collected to establish the experimental database.•Model for predicting the complete stress-strain curve of FRP and steel spiral-confined concrete was proposed.•The proposed model can simulate the complete stress-strain curve well and has better flexibility and versatility.