Abstract
Axial compression tests were carried out on 72 FRP (fiber reinforced polymer)–stirrup composite-confined concrete columns. Stirrups ensure the residual bearing capacity and ductility after the FRP fractures. To reduce the effect of stress concentration at the corners of the confined square-section concrete columns and improve the restraint effect, an FRP–stirrup composite-confined concrete structure with rounded corners is proposed. Different corner radii of the stirrup and outer FRP were designed, and the corner radius of the stirrup was adjusted accurately to meet the designed corner radius of the outer FRP. The cross-section of the specimens gradually changed from square to circular as the corner radius increased. The influence of the cross-sectional shape and corner radius on the compressive behaviour of FRP–stirrup composite-confined concrete was analysed. An increase in the corner radius can cause the strain distribution of the FRP to be more uniform and strengthen the restraint effect. The larger the corner radius of the specimen, the better the improvement of mechanical properties. The strength of the circular section specimen was greatly improved. In addition, the test parameters also included the FRP layers, FRP types and stirrup spacing. With the same corner radius, increasing the number of FRP layers or densifying the stirrup spacing effectively improved the mechanical properties of the specimens. Finally, a database of FRP–stirrup composite-confined concrete column test results with different corner radii was established. The general calculation models were proposed, respectively, for the peak points, ultimate points and stress–strain models that are applicable to FRP-, stirrup- and FRP–stirrup-confined concrete columns with different cross-sectional shapes under axial compression.
Highlights
College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China; Jiangsu Expressway Engineering Maintenance Technology Co., Ltd., Nanjing 211106, China
The failure modes of the plain concrete column specimens (PC-C series and PC-S series) were failure modes of the plain concrete column specimens (PC−C series and PC−S series) basically the same under the axial compression tests
Most of the existing stress–strain models of fibrereinforced polymers (FRPs)–stirrup composite-confined concrete columns only consider the change in the stress–strain relationship curve before the concrete column structure reaches its ultimate bearing capacity, and only a few stress–strain models can be used for predicting the descending curve after FRP fracture
Summary
Seventy-two FRP–stirrup composite-confined concrete columns with heights of 300 mm were designed and tested under axial compression. Because when stirrups are used to restrain concrete columns, the shape design of stirrups is usually consistent with the cross-sectional shape of specimens, so the corner radii of the stirrups (r) are adjusted accurately to meet the corner radius of the outer FRP. The cross-sections of the specimens gradually changed from square to circular as the corner radii increased. According to the type of external FRP (CFRP or BFRP), the specimens were divided into two batches. The specimens were coded according to their cross-sectional shape (S: square), corner radius (R: 5, 25, 40, and 75 mm), stirrup spacing (S: 20, or 40 mm), FRP type (B: BFRP, and C: CFRP).
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