Study on the Pressure Properties and Bearing Capacity of Concrete Filled Steel Tubular Columns under Constant High Temperature Effect YANG Hua, HAN Linhai 2 (1. Harbin L: College of Physics, Harbin University, Harbin 150090, China; 2. School of Civil Engineering and Architecture, Fuzhou University, Fuzhou 350002, China) The variation of the pressure properties and strength bearing capacity of concrete shafts. The basic parameters of the test are temperature from 20t to 900T. Based on the core concrete mechanical model of the CFST short test piece at normal temperature, the mechanical model of the core concrete after constant temperature action is established. The results show that the CFST axial compression members still have better deformation resistance and later bearing capacity; the residual strength and modulus of CFST decrease with the increase of constant temperature. The numerical simulation method is used to calculate the axial load-deformation curve of concrete-filled steel tube after constant high temperature action. The theoretical calculation results are in good agreement with the experimental results. Based on this, the axial compressive bearing capacity and axial compression modulus of concrete filled steel tube after high temperature action are proposed. Simplify the juice calculation formula.

Combined effect; Strength Carrying Capacity Fund Project: National Natural Science Foundation Grant H (5958007); Huo Yingdong Education Funded by the Ministry of Education Funded by the Outstanding Young Teachers Fund, the concrete filled steel tube has high bearing capacity, good plasticity and toughness. Advantages of good seismic performance, convenient construction and good economic results. I test results show that in the fire, the steel tube and core concrete which make up the concrete filled steel tube have the advantages of mutual contribution, synergistic complementarity and common work, which makes the fire resistance better than the steel structure. . After the fire, with the decrease of the external temperature, the strength of the steel tube at the yield section of the CFST was restored to different degrees, and the mechanical properties of the section and the integrity of the structure were improved compared with the high temperature.

It can be seen that the performance of concrete filled steel tube after fire has its characteristics, and its strength and mechanical properties should be reasonably evaluated.

At present, the research on the fire resistance of concrete-filled steel tubes has been carried out at home and abroad. However, most of the research on structural damage after fire has focused on reinforced concrete structures and steel structures. "1, there is no report on the research on steel-tube concrete. Therefore, It is necessary to study the mechanical properties and bearing capacity of CFST after constant temperature action, which is provided for further research work.

1 Stress-strain relationship model of steel and concrete after constant high temperature 1.1 Steel test research shows that Pl, structural steel specimens subjected to high temperature and natural cooling have the same necking phenomenon as normal temperature when they are close to failure. The elastic modulus is the same as the normal temperature, and the yield strength can be expressed by the following formula for analysis. The double-fold line model is used as the stress-strain relationship of the steel after constant high temperature action, see equation (2).

4 (7) is the standard value of concrete compressive strength after constant high temperature. According to the calculation, formula (4) has actually considered the constraint effect of steel pipe on core concrete. That is, the relationship between the core concrete and the core of different confinement effect coefficients after the concrete tube concrete temperature of 7=600 is calculated according to formula (4). It can be seen that the relationship curve of concrete shows a trend of rising, gradual or decreasing with the difference of values. The larger the A value is, the smaller the decrease is and the lower the segment is not. On the contrary, the smaller the value, the larger the decrease.

The whole process analysis of the 2-axis compressive load-deformation relationship curve is carried out by numerical analysis method, and the whole process curve of the axial compression load-deformation of the concrete filled steel tube with different constant high temperature effects is calculated. The following basic assumptions were adopted in the calculation. Beijing: Science Press, 2000. P Cao Wen. Analytical study on fire response of steel frame structures under damage accumulation conditions. Shanghai: Tongji University, 1998. Dong Yili. Overview of civil fire research. Beijing: Xiangshan Science Conference, 1997: 1-7. Lu Zhoudao, Zhu Bolong, Tan Wei. Research on reinforcement and repair of reinforced concrete beams after fire. Shanghai: Proceedings of the State Key Laboratory of Civil Engineering Disaster Prevention. 〗 993: 152-162. Wu Bo, Yuan Jie, Wang Guangyuan. Experimental study on mechanical properties of bare concrete after enthalpy. Journal of Civil Engineering, 2000, (2): 8-12. Guo Zhenhai, Li Wei. Deformation test and constitutive relationship of concrete under different stress-temperature paths.

Yang Hua. Study on the axial behavior of concrete-filled steel tubular columns after constant high temperature action. Harbin: Harbin University of Architecture, 2000.

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