Axial compression behavior of CFRP-confined rectangular concrete-filled stainless steel tube stub column

Abstract

The mechanical properties of CFRP-confined rectangular concrete-filled stainless steel tube (CFSST) stub columns under axial compression were experimentally studied. A total of 28 specimens (7 groups) were fabricated for the axial compression test to study the influences of length-to-width ratio, CFRP constraint coefficient, and the thickness of stainless steel tube on the axial compression behavior. The specimen failure modes, the stress development of stainless steel tube and CFRP wrap, and the load–strain ratio curves in the loading process were obtained. Meanwhile, the relationship between axial and transverse deformations of each specimen was analyzed through the typical relative load−strain ratio curves. A bearing capacity prediction method was proposed based on the twin-shear strength theory, combining the limit equilibrium state of the CFRP-confined CFSST stub column under axial compression. The prediction method was calibrated by the test data in this study and other literature. The results show that the prediction method is of high accuracy.

Graphical abstract

Keywords

CFRP / rectangular CFSST stub column / bearing capacity / limit equilibrium state / twin-shear strength theory

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Acknowledgements

This study was generously funded by the National Natural Science Foundation of China (Grant No. 51268044). The first author also appreciates the support from the University of Pittsburgh and North Dakota State University when he worked as a visiting scholar.

Notations

A _c: cross-sectional area of core concrete

A _cfst: total cross-sectional area of carbon steel tube and core concrete

A _fr: cross-sectional area of CFRP wrap

A _s: cross-sectional area of stainless steel tube

B: short side of rectangular steel tube

DI: ductility index

E ₀: elastic modulus of stainless steel

E _fr: elastic modulus of CFRP sheet

H: specimen height

f _ck: vcharacteristic strength of concrete

f _cu: standard cubic compressive strength of concrete

f _cfst: strength index of concrete in rectangular stainless steel tube under axial compression

f _fr: tensile strength of CFRP sheet

L: long side of rectangular steel tube

n: hardening exponent of stainless steel

n _f: number of CFRP layers

N: load

N _cfr: predicted load-carrying capacity

N _cfst: bearing capacity of concrete-filled stainless steel tubular stub columns with rectangular section under axial compression

N _cr: calculation value of ultimate bearing capacity of concrete-filled rectangular stainless steel tubular short columns

N _p: proportional limit load

N _r: residual load capacity of the FRP-confined CFSST after full fracture of CFRP wrap

N _u: peak load at failure

t _fr: CFRP thickness

t _s: wall thickness of stainless steel tube

Δ: axial deformation

Δ ₁: axial deformation corresponding to the feature point

Δ _u: axial deformation corresponding to ultimate strength

ε _85%: axial strain when the load falls to 85% of the ultimate load

ε: strain of stainless steel

ε _a,s: longitudinal strain

ε _h,s: transverse strain

ε _y: ε _75%/0.75, where ε _75% is the axial strain when the load attains 75% the ultimate load in the pre-peak stage

ε _p: corresponding axial strain of proportional limit load

ε _r: corresponding axial strain of the lowest point at failure

ε _u: corresponding axial strain of the peak load at failure

η _fr: improvement of specimen bearing capacity

φ: sectional stability coefficient

ν: lateral-to-axial strain ratio

σ _0.2: 0.2% proof stress of stainless steel

ξ _fr: confinement factor of CFRP wrap

ξ _s: confinement factor of stainless steel tube

υ: Poisson’s ratio

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