Axial stress–strain relationship for FRP confined circular and rectangular concrete columns

A general mathematical model is developed to describe the stress–strain (f_c–ε_c) relationship of FRP confined concrete. The relationship is applicable to both circular and rectangular columns, and accounts for the main parameters that influence the stress–strain response. These include the area and material properties of the external FRP wraps, the aspect ratio of rectangular column sections, the corner radius used for FRP application, and the volumetric ratio and configuration of internal transverse steel. The proposed model reproduced accurately experimental results of stress–strain or load–deformation response of circular and rectangular columns. In addition to its importance in evaluating the effect of FRP confinement on the ultimate axial strength of concrete columns, the developed f_c–ε_c relationship can be employed very efficiently and effectively for analyzing the response of FRP confined concrete under different types of load application.     

Behavior of air-entrained concrete under the compression with constant confined stress after freeze–thaw cycles

Properties of air-entrained concrete under compressive loads with constant confined stress after 0, 100, 200, 300 and 400 cycles of freeze–thaw were studied. The failure characteristic of specimens and the direction of the crack are observed. Based on the test data, the influence of freeze–thaw cycles and lateral compressive stress ratio on the ultimate compressive strength is analyzed, respectively. The relationships between the ultimate compressive strength and freeze–thaw cycles, lateral compressive stress ratio are given, respectively. The unified failure criterion with consideration of the influence of freeze–thaw cycles and stress ratio is proposed. It provides the experimental and theory foundations for strength analysis of air-entrained concrete structures subject to complex loads in cold environment.