Comparative study of stirrup-confined circular concrete-filled steel tubular stub columns under axial loading

Abstract

This paper presents a comparative study of circular concrete-filled steel tubular stub columns with three different stirrup confinement types: bidirectional stirrups, loop stirrups and orthogonal stirrups. Axial compression tests have been carried out aiming at investigating the effects of the stirrup form and volume-stirrup ratio on the mechanical behavior of the stirrup-confined circular CFT stub columns, and ABAQUS was used to carry out the 3D numerical modelling. Radial stress of the core concrete and the composite action among the steel tube, stirrups and the core concrete have been investigated. It is found that the confinement provided by stirrups on core concrete strongly outperforms that provided by steel tube, steel sections or steel reinforcement. Furthermore, a simplified approach was developed to predict the ultimate bearing capacity of stirrup-confined circular CFT stub columns, which agreed well with the experimental and numerical results.

Confinement Effect and Efficiency of Concentrically Loaded RACFCST Stub Columns

“…The expression is as follows [ 29 ]: where σ i is the equivalent stress; f u is the ultimate strength of steel, which is equal to 1.5 times the yield strength f s ; the Young’s modulus E s is 2.06 × 10 5 MPa; ε i stands for the equivalent strain of steel; ε y means the yield strain; ε st means the hardening strain and is equal to 12 times ε y ; ε u is the ultimate strain and is equal to 120 times ε y ; and ζ is a parameter chosen as 1/216. This steel model has been verified in previous studies of concrete-filled steel tubular columns subjected to axial loading [ 31 , 32 , 33 , 34 ], shear [ 35 ], torsion [ 36 ], and cyclic loading [ 37 ]. The stress–strain relations of steel derived by the adopted model with different yield strengths is shown in Figure 4 .…”

“…This discrepancy between the two methods was considered due to the constitutive relation of the steel tube in the FE analysis, which could not perfectly reflect the stress–strain curves of the steel tube in the test, especially in the hardening stage. According to the existing experimental tests, local buckling could be occasionally observed on the outer steel tube, while the specimen reached the ultimate loading capacity [ 31 ], and the hardening of steel enhances the confinement effect of the steel tube on the infilled concrete. Hence, compensating for the confinement effect of the steel tube in FE analysis and combining with the limit equilibrium method and experimental data verification, the confinement coefficient of CFCST stub columns subjected to axial load is recommended as 1.7.…”

Mechanical performances of high‐strength concrete‐filled steel tubular medium–long columns with square cross section

“…When the displacement specified in the current stage is reached, loading was paused for 5 min and continued loading until the specimen is damaged. 43 During the test, the DH3821 static strain test and analysis system 44 was used in the tests. The system can collect the strain gauge data and displacement meter data of the specimen, such as axial displacement, lateral deflection, and strain of the specimen, in real time, and store these data together with the force on the press simultaneously.…”

Numerical Study on Confinement Effect and Efficiency of Concentrically Loaded RACFRST Stub Columns

“…The steel stress-strain curves could reflect the composite action and the intersection of the axial stress-strain curve and the transverse stress-strain curve represents the best composite action point of the composite structures. The earlier the intersection of the axial stress-strain curve and the transverse stress-strain curve occurred, the better the composite action and the confinement efficiency were (Ding et al, 2018b). Hence, the indexes mentioned above were utilized herein to evaluate the confinement effect and efficiency as the design parameters change.…”