Unified cyclic stress-strain model for FRP-confined concrete circular, square and rectangular prisms

The behaviour and modelling of concrete columns confined with FRP composites under monotonic compression has been extensively studied, but far fewer studies of the cyclic behaviour of FRP-confined circular and rectangular columns have been carried out. A reliable model indicating the cyclic stress-strain behaviour of FRP-confined columns is of great importance, especially for seismic retrofits and the design of these columns. In this paper, based on the results from a series of cyclic compressive loading tests on FRP-confined specimens, a unified cyclic stress-strain model is proposed for circular, square and rectangular columns confined with FRP composites. The model contains different parts of the cyclic stress-strain curve, including plastic strain, maximum strain in unloading path and corresponding stress, stress deterioration, effect of loading history, partial unloading and partial reloading. New expressions are also proposed for predicting unloading and reloading paths. The proposed model agrees well with the test results.