Elasto-Plastic Analysis Of Slender Circular Tubular Steel-CFRP Column

CFRP has the characteristics of fatigue resistance,corrosion resistance,high tensile strength,and design modulus.Combining and optimizing it with other traditional structures can achieve higher performance.At present,the research of CFRP in the field of civil engineering application mainly focuses on the strengthening existing structures,while the research on new CFRP composite structures is still in its infancy.This research focuses on the stability of Circular-section steel-CFRP composite slender columns.The main research contents are as follows:1.Based on the assumption of small elastic deformation,this research proposes a calculation method for the critical instability load of a slender column under the condition of elastic hinge support in the elastic range.The theoretical calculation formula of the deflection curve considering the imperfection in the elastic range is established.On this basis,this study further discusses the deflection curve influence function under specific load levels.2.This study simplifies the stiffness of the variable stiffness slender column,and proposed an approximate calculation method for the critical instability load of the variable stiffness slender column under the condition of elastic support.Under the condition of simplified stiffness,the theoretical calculation formula of deflection curve considering the imperfection is given.After that,this study discusses the factors affecting the plasticity of long columns and the development of plasticity during the instability of long columns.3.Based on the theoretical analysis in this research,the stability analysis program of the circular section steel-CFRP composite slender column is developed.The analysis methods for the elastic and plastic phases of the composite structure are designed respectively,and the analysis process that can be applied to the elastic and plastic analysis is proposed.Finally,the program analysis result is compared with an experiment,and the program analysis result fits well.4.Based on the self-developed program,this paper studies the effects of spring hinge stiffness,initial geometric defects,initial load eccentricity and residual stress on the stability of circular section steel-CFRP composite slender columns.The analysis results show that these factors make the stable bearing capacity of the composite structure increased by 26.8% to a decrease of 13.12%.In addition,the stable bearing capacity formulas of the bars under different parameters and different CFRP layers are fitted.The formula shows that it is appropriate to think that the influence of the number of CFRP layers on the bearing capacity of the composite slender column is independent of the influence of other factors on the bearing capacity.This research is carried out along the process of theoretical analysis,numerical analysis,program development,and parameter analysis.Through further research on the stability theory,the numerical analysis process is simplified and the computational efficiency of the numerical analysis program is improved.This method can greatly reduce the time required for calculation under the premise of better guarantee of calculation accuracy.This research has improved the theoretical analysis level of member stability and promoted the transformation of CFRP composite structure from scientific research to practical application.