| Circular concrete-filled steel tube(referred to as CCFST)has the characteristics of high bearing capacity,good ductility and easy construction due to the interaction of concrete and steel pipe.Under the action of bias pressure,although there is good synergy between the core concrete and steel pipe components at work,the material properties of steel and concrete are different,and the force condition of bias-pressure members is more complicated compared with axial pressure,which makes its bearing capacity calculation quite cumbersome.At present,although the theoretical basis of the calculation method of CCFST biased compression members at home and abroad are different,a large number of parameters are still obtained through regression analysis of test data,and there are certain limitations in its scope of application,so it is necessary to establish a formula for calculating the bearing capacity of positive section of CCFST members under different stress conditions.In this thesis,based on superposition theory,the limit equilibrium method and equivalent steel strip method are used to study the force mechanism,positive section bearing capacity calculation and section design method of CCFST biased short column,the specific work is as follows.(1)Citing the method of equivalent rectangular stress diagram coefficients,the reasonable values of ultimate compressive strain of CCFST compressed members are discussed.Based on Hanlinhai’s principal structure model,the curves of equivalent rectangular stress coefficients α and β of restrained concrete are calculated and the suggested values are obtained by using MATLAB,which lay the foundation for calculating the stresses of concrete in the compressed zone in the later thesis.(2)Based on the superposition theory,the limit equilibrium method and the equivalent steel strip method are used to derive and optimize the equations of the positive section bearing capacity of CCFST biased short columns under three types of stresses,124 test results of CCFST biased short columns at home and abroad are collected and a database is established.The calculation results of GB50936-2014 code,CECS:28:2012 code,JCJ 01-89 code,AISC 360-10 code,and AIJ code are compared with the results of this thesis,and the causes of errors of this thesis’s formula are analyzed.(3)Based on the drawing principle of Nomogram,the cross-sectional design diagram algorithm for CCFST biased short column is proposed for CCFST biased(compression-bending)short column,and the n-m-ξ Nomogram which can be used for multiple purposes is designed,and the process of its use is demonstrated by the calculation example to provide convenience for engineering design.(4)Relying on MATLAB numerical analysis platform,the fiber model of CCFST is established,and the whole process analysis curve of N-um is compared with the experimental measurement results to verify the reliability of the fiber model;in addition,using the experimental data points as reference,the N-M correlation curves calculated by the numerical model,several sets of typical domestic and foreign regulations and the formulae in this thesis are compared and analyzed,and the reliability of each set of algorithms on the bearing capacity of the member under different conditions is evaluated.In addition,the N-M correlation curves obtained from the numerical model,several sets of typical regulations at home and abroad and the formulae in this thesis are compared and analyzed to evaluate the prediction effect of each set of algorithms on the bearing capacity of the members under different conditions and analyze the reasons for it,which further illustrates the rationality of the formulae in this thesis. |
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