Researches On Models Of Stress-Strain And Applications In Rehabilitation For Concrete Confined By FRP

Fiber reinforced polymer or plastics has been widely used as a new material for strengthening existing civil infrastructures, due to their advantages in the high tensile strength, light weight, ease for construction, no addition to dimensions of members etc. Especially in the aspects of upgrading columns and piers, FRP can effectively improve their compressive performances by restricting the lateral dilation of confined concrete. There have been a number of studies on the uses of this technique, but theoretic researches of that still drop behind its applications in construction and need being further perfected. This paper collects related studies during recent decades, analyzes the constitutive relationships of confined concrete and mechanical performances of reinforced concrete column wrapped by FRP covering experiments of rectangular columns compressed under axially, eccentrically loading. The main contents and achievements of this paper are summarized as following:Several typical models including stress, strain and stress-strain relationship for concrete cylinder confined by FRP are listed, and the models of stress, strain for peak point are compared according to over 250 collected experimental members. Besides, the parameters of unconfined concrete strength, lateral confining strength of FRP and so on are analyzed quantitatively.The mechanism of concrete confined by FRP and its differences relative to steel confining are explained. Many related experimental data indicates the ring tensile strain of FRP confining concrete cylinder is different from the flat tensile strain, and leading causes are analyzed, so the existed lateral confining strength can't represent its actual value, then this paper presents a calculating formula of new effective lateral confining strength. This chapter analyzes the curves shape of stress-strain relationship of concrete cylinder confined by FRP, finds its characteristics can be simulated by a simplified multi-linear curve; presents a new calculating formula for lateral expansion coefficient according to lateral confining strength, unconfined concrete strength, which refers to existed rule of lateral expansion coefficient with steady value in the ultimate state. Based on the developing characteristics of volumetric strain and lateral expansion coefficient, the function mode for judging concrete confined by FRP strongly or not, and then the determined formula is put forward according to regressive analyzing based on related experimental data. The relativity between stress, strain of confined concrete and load path is analyzed, and the strength is not load path-dependent, but the strain is path-dependent. At last, the models of stress, strain and stress-strain relationship are presented considering concrete confined by FRP strongly or weakly. For concrete confined weakly, due to the complexity of descending ultimate point, a reference point with 1.9 times peak strain is used to confirm the descending line.This chapter compares the existed calculating models of axial stress, strain and axial stress-strain of confined concrete confined by FRP with rectangular section, expresses the differences for FRP confinement between rectangle and cylinder and the main characteristics of rectangular section concrete confined by FRP. Based on the related experimental data, the discount coefficient of tensile strength of FRP wrapping rectangular section is determined considering the weakening due to stress concentration on corner; the influences of section shape, length/width accepts the method advised by Teng et al. Considering the above...