Bearing capacity of rectangular concrete-filled steel tube (CFST) and dumbbell shaped CFST under axial compression, eccentric compression, and pure bending stress states

The fiber model method utilizes material constitutive relationships and internal force synthesis techniques to accurately and conveniently determine the internal force of the section, without the need to establish an element stiffness matrix. It is simple and practical and has been widely used in the bearing capacity analysis of concrete-filled steel tubes (CFST). The material constitutive relationship is an important factor determining the calculation accuracy of the fiber model method. This article studies and establishes a modified model for the constitutive relationship of CFST materials, and establishes the fiber model method for the mechanical performance analysis of rectangular CFST and dumbbell CFST, respectively. Based on the geometric size parameters and material strength parameters (such as "length", "Diameter", "Width", "Thickness", "Yield strength", "Compressive strength", etc.) in the experimental database, the fiber model method is used to calculate the bearing capacity of the component and compare it with the "Test values" in the experimental data to verify the calculation accuracy and applicability of the fiber model method and the established constitutive relationship.

The test database contains a total of 6 tables. Table 1.1 shows the axial compression test database for rectangular sections, with a total of 428 sets of data; Table 1.2 shows the pure bending test database for rectangular sections, with a total of 84 sets of data; Table 1.3 shows the database of compression bending tests for rectangular sections, with a total of 208 sets of data. Table 2.1 shows the database of axial compression tests for dumbbell shaped sections, with a total of 20 sets of data; Table 2.2 shows the pure bending test database for dumbbell shaped sections, with a total of 4 sets of data; Table 2.3 shows the database of compression bending tests for dumbbell shaped sections, with a total of 30 sets of data.

Methods
(1)The test data is derived from domestic and international literature, involving different concrete strength indicators. For the convenience of comparative analysis, this paper unifies the different strength indicators into axial compressive strength fck: when the compressive strength of the cylinder, fc’<=40MP, the compressive strength of the cube, fcu,k=1.25*fc’; otherwise, fcu,k=fc’+10. The axial compressive strength fck can be calculated using the formula fck=0.88x0.4x(fcu,k)7/6.

(2) The test database uses parameters such as length, diameter, and eccentricity to describe the member information. When these parameters are not directly provided in the reference literature, they are obtained by converting other known parameters in the original literature.

(3) In the absence of a specific value for the elastic modulus of the steel pipe in the literature, a standardized value of Es = 206,000 MPa is uniformly adopted to facilitate computational analysis.

(4) In order to make the test database clear at a glance, the length unit of the test database is mm, the strength unit is MPa, the force unit is kN, and the moment unit is kNm. When the units of various data in the reference literature are different from those in the test database, unit conversion is performed.