Most previous studies on concrete short columns confined with fiber-reinforced polymer (FRP) composites were based on small-scale testing, and size effect of the columns still has not been studied thoroughly. In this study, 99 confined concrete short columns wrapped with aramid FRP (AFRP) jackets and 36 unconfined concrete short columns with circular and square cross sections were tested under axial compressive loading. The circular specimens were divided into six groups, and the square specimens were divided into five groups, with each group containing different levels of the AFRP’s confinement. In each group, the specimens were geometrically similar to one another and had three different scaling dimensions. Statistical analyses were used to evaluate the size and interaction effects between the specimen size and the AFRP’s confinement, and a size-dependent model for predicting the strength of the columns was developed by modifying Bazănt’s size-effect law. The experimental results showed that the size of...

The mechanical deterioration of concrete exposed to freeze-thaw cycles is one of the most important durability problems under subzero temperature conditions. At present, studies on concrete behavior under freeze-thaw cycles primarily focus on the degradation of concrete properties, there are few reports on testing and modeling the stress-strain relationships of concrete undergoing repeated cycles of freeze-thaw. This paper investigated the stress-strain relationship of fly ash concrete under 0, 5, 15, 30, 50, 75, 100, and 125 freeze-thaw cycles by testing 24 prism specimens. The relative dynamic modulus, compressive strength, elastic modulus, and stress-strain relationship of specimens under freeze-thaw cycles were measured. In addition, a multiple sharp degradation point model for the degradation of mechanical properties of concrete was proposed. Finally, a damage constitutive model on the base of the damage mechanics and the multiple sharp degradation point model was presented. By comparing the ...