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. In this work, the axial response of plain concrete under varying confining pressure was examined using a novel triaxial cell mechanism. This work examines realistic levels of 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 developed with using the results from companion experimental program. The model is based on the variation of the confining pressure due to the lateral dilation of the concrete. The model is shown to provide an accurate prediction of historical experimental studies of constant confinement tests on cylinders, FRP jacketed specimens, and columns confined with conventional lateral reinforcement or FRP jackets.