Study On Eccentric Compression Behavior Of Thin-walled Steel Confined Square Timber Columns

With the formulation of national policies and the implementation of standardized standards,the development of wood structure is very rapid.As a material,wood has many quality defects,including natural defects,biological hazard defects and processing defects.The lignified tissue in wood leads to significant differences in compressive strength and shear strength along and across grain,which limits the application of traditional wood structure.However,steel has many advantages such as isotropy and uniform material.Therefore,scholars at home and abroad put forward the concept of using steel to restrict wood columns,using steel to limit the transverse deformation of wood,and using wood to limit the local buckling of steel,so as to improve the mechanical performance of traditional pure wood columns.However,they mainly carry out the research on the axial compression performance of composite wood columns,including the failure process,failure mode The mechanical performance and corresponding calculation and analysis methods need to be studied.In view of this,based on the research on the mechanical performance of the steel wood combination of the research group,this paper uses the thin-walled steel to restrict the square wood column and uses the high-strength bolt to pull,so that the composite wood column makes full use of the high-strength tensile strength of the steel under the stress state,so that the thin-walled steel cylinder and the square wood column can coordinate the deformation.In order to comprehensively study the mechanical properties of thin-walled steel confined square timber columns under eccentric compression,the following research work is carried out in this paper:(1)Test on mechanical properties of basic materials of wood and steelConduct mechanical property test on the materials required in this test.Firstly,the wood property test of wood is carried out,and the experimental data are sorted out to obtain the Poisson’s ratio,elastic modulus,yield compressive strength and ultimate compressive strength of wood in the longitudinal,radial and chord directions;According to the existing specifications,the shear modulus on three shear planes of wood is calculated.Through the tensile test of steel,the yield tensile strength and ultimate tensile strength of thin-walled steel tensile samples are obtained.(2)Experimental study on eccentric compression performance of thin-walled steel confined square timber columnsNine thin-walled steel confined square timber columns and two pure timber columns were used in the eccentric compression test.In the test,the failure process of each specimen is obtained,the failure mode of the specimen is analyzed,the ultimate bearing capacity of the specimen is sorted out,and the load displacement and load strain data of each specimen are obtained.The load displacement curve and load strain curve of thin-walled steel confined square timber column under eccentric distance and slenderness ratio are analyzed.At the same time,the ultimate bearing capacity,ductility coefficient,longitudinal stiffness and working mechanism of thin-walled steel confined square timber column under eccentric compression are also analyzed.The results show that under the condition of the same slenderness ratio,the thin-walled steel confined square timber column is affected by the eccentricity,that is,the greater the eccentricity,the ultimate bearing capacity of the thin-walled steel confined square timber column decreases by 29%-36%,the longitudinal stiffness decreases by 9%-31%,and the ductility coefficient increases by 14%-92%;Under the condition of the same eccentricity,the greater the slenderness ratio of thin-walled steel confined square timber column,the ultimate bearing capacity of thin-walled steel confined square timber column decreases by 5%-17%,the longitudinal stiffness decreases by 9.5%-33%,and the ductility coefficient increases by 9%-69%.The comparative analysis shows that the eccentricity factor has a great influence on the mechanical properties of thin-walled steel confined square timber columns.In addition,this paper also compares the mechanical properties of pure wood column and thin-walled steel confined square wood column under eccentric compression.The test shows that the thin-walled steel confined square wood column shows better mechanical properties than pure wood column due to the restraint effect of thin-walled steel active confining pressure.(3)Finite element simulation analysis of thin-walled steel confined square timber columns under eccentric compressionIn order to further study the eccentric compression performance of thin-walled steel confined square timber columns and lay the foundation for the subsequent analysis of the calculation and analysis methods of thin-walled steel confined square timber columns,this paper will establish the numerical analysis model of thin-walled steel confined square timber columns by using ABAQUS finite element analysis software to analyze the eccentric compression performance of thin-walled steel confined square timber columns.According to the finite element simulation calculation and analysis,the mechanical effects of slenderness ratio and eccentricity on thin-walled rigid confined square timber columns are further studied.The numerical simulation results are consistent with the eccentric compression test results of thin-walled steel confined timber columns.(4)Calculation of bearing capacity of square timber short columns restrained by thin-walled steel under eccentric compressionAccording to the calculation formula of eccentric compression of square timber column in various national design codes,it is analyzed that the calculation formula in the code adopts linear theory,which shows that the calculation method of bearing capacity of square timber column should adopt nonlinear theory,and the calculation formula of bearing capacity of square timber column is put forward.Referring to the calculation formula of eccentrically compressed bearing capacity of concrete-filled steel tubular in existing literature,the calculation methods of ultimate bearing capacity,limit equilibrium method and unified theory method of thin-walled steel confined square timber columns are analyzed.In this paper,the reduction coefficients of eccentricity and slenderness ratio are derived by using the unified theory method,and the relevant reduction coefficient curve formulas are fitted.Finally,the calculated data are compared with the experimental data.