Abstract
This study investigates the suitability of the circularization technique for strengthening square concrete-filled square steel tube (CFSST) short columns. A total of 16 specimens were tested under axial compression. The main parameters under investigation were concrete strength, the thickness of arc cement mortar layer components (CAM), and the layers of carbon fiber-reinforced polymer (CFRP) sheets. Test results indicated that the failure mode of CFRP-confined circularized CFSST (C-C-CFSST) columns was similar to that of CFRP-confined concrete columns. The CFRP-confined circularized strengthening method can increase confinement efficacy and reduce the stress concentration at the corners of CFSST columns. Three existing CFRP-confined concrete stress-strain models were evaluated using the test results. The predictions of the Lam and Teng stress-strain model agree well with the test data.
Highlights
Concrete-filled steel tube (CFST) has the advantages of high bearing capacity and ductility and is widely used in civil structures [1, 2]
Hadi et al carried out relevant research on the CFRPconfined arc-treated concrete rectangular columns; the results show that using precast concrete arc-treated components as transitions between carbon fiber-reinforced polymer (CFRP) and rectangular columns could significantly reduce stress concentration and enhance the effective constraint area of the cross section [20, 21]. e above studies showed that circularizing concrete columns by bonding precast segments can increase the axial load capacity and change the stress-strain curve from softening to hardening the branch of reinforced concrete (RC) columns [20]
Main Test Results. e key test results of axial compression specimens are shown in Table 3. fc0 is the compressive strength of unconfined concrete columns, fco′ is the compressive strength calculated value of concrete-filled square steel tube (CFSST), and N is the ultimate bearing capacity of specimens
Summary
Concrete-filled steel tube (CFST) has the advantages of high bearing capacity and ductility and is widely used in civil structures [1, 2]. To improve the confinement efficiency of CFSST columns by CFRP jackets and to reduce stress concentration, the circularizing technique has been proven to be an effective method before FRP wrapping by some scholars. Yang et al performed an experimental study on the axial compressive performance of rectangular concrete-filled FRP-steel composite tube columns for various corner radiuses and proposed that FRP-confined CFSST concrete stress-strain curve can be divided into four phases (i.e., initial linear phase, transition to yield phase, hardening phase, and residual phase). Erefore, shape modification before FRP wrapping may effectively reduce stress concentration To solve this problem further, an experimental study was undertaken to investigate the suitability of the circularization technique for strengthening CFSST short columns. Sixteen specimens were tested under axial compression to study the influence of different CAM thicknesses (the middle height of CAM component), layers of CFRP, and concrete strength on bearing capacity, deformation performance, and stressstrain relationship
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