A predictive methodology for estimating the axial response of confined concrete

The axial strain-axial stress behavior of confined concrete plays a vital role in the design of concrete column members; hence an accurate prediction of the stress-strain behavior is needed. A variety of models that have been developed previously were summarized to provide background information. A preliminary experimental program was conducted with three jacketing applications (carbon fiber reinforced polymer (FRP), glass FRP, and steel) and compared with the current predictor models and finite element estimations. Two categories of predictor models were examined: Constant Confinement models (CC) and Variable Confinement models (VC). The CC model assumes that the confining pressure provided by the jacket (at the ultimate strength of the confining material) is active and constant over the load history. VC model assumes that the confinement passively increases as lateral dilation occurs. The preliminary experimental program shows that VC models provide an improvement over CC models for accurately predicting the stress strain response of confined concrete. The conceptual limitations to these methods are clearly illustrated through examples.; A detailed experimental program was conducted using a novel triaxial cell mechanism. The axial response of concrete under varying confining pressure was examined. To evaluate the axial response of confined concrete under realistic conditions, the pressure produced by triaxial cell mechanism is controlled through lateral strain feedback. The study examines constant, linear elastic, elastic - perfectly plastic, and elastic-hardening varying confinement, typical of fiber reinforced polymer and steel jacketing applications. It is found that the axial stress-strain response of confined concrete is dependent on the variation of confining pressure applied.; A unique model for estimating the axial response of concrete under varying or constant levels of confinement is empirically developed. The axial stress-strain response is defined into three regions separated by two characteristic response levels. The model is based on the variation of the confining pressure due to the lateral dilation of the concrete. An estimate of dilation with respect to axial strain is also developed. The model is shown to provide an accurate prediction of historical experimental data of concrete confined with various jacketing and reinforcement applications.