| Since the beginning of the new century,with the continuous exploration of the mechanical properties of cold-formed steel by Chinese steel structure researchers and the rapid development of steel processing technology,the production of cold-formed steel components with a wall thickness of 20 mm is no longer a difficult task for our country.,Cold-formed thick-walled steel axial compression components are also increasingly used in the construction of large-scale projects.However,since the promulgation of the "Technical Specification for Curved ThinWalled Steel Structures"(draft)in 1969,the wall thickness of cold-formed steel axial compression components in my country’s specifications has been limited to between 2 and 6mm.Although China’s GB50018-2002 "Technical Specification for Cold-Formed Thin-Walled Steel Structures" promulgated in the early 21 st century considered and discussed this issue,due to the lack of a large amount of test data support and insufficient research experience,the China Thin Steel Specification It was decided to still keep the limit on the wall thickness.The application and development of cold-formed thick-walled axial compression components in my country are severely restricted.To this end,this paper relies on the 13 th Five-Year Key R&D Program sub-project: High-efficiency section steel structure application technology(2018YFC0705503-2),and systematically researches the mechanical properties of cold-formed thick-walled rectangular section axial compression members.The main research contents and conclusions are as follows:Completed the tensile test of 21 material specimens(including flat specimens and bent angle specimens).The results show that the difference between the elastic modulus of the flat specimen and the curved specimen is very small,and it is very close to the modulus of elasticity2.06×105 MPa adopted in the Chinese standard.Therefore,it can be concluded that the coldbending effect has basically no effect on the elastic modulus of cold-formed thick-walled steel.Due to the cold bending effect of the steel,the yield strength of the flat specimen is about 5%higher than that of the base material,and the yield strength of the curved specimen is much greater than that of the flat plate,which is about 50%.Axial compression tests of 15 cold-formed thick-walled rectangular cross-section specimens were carried out,and the instability mode and stable bearing capacity of the coldformed thick-walled square rectangular cross-section axial compression member were obtained.Among them,the specimen with a length of 1200 mm experienced overall bending instability around the weak axis,and was accompanied by local buckling of the section.The specimens with lengths of 1800 mm,2400mm and 3000 mm all experienced bending instability around the weak axis as a whole.For specimens with a specimen length of 600 mm,the instability mode is characterized by local buckling.A finite element model considering initial geometric defects and cold-bending residual stresses was established,and combined with experimental phenomena and experimental data,the accuracy of the model was verified after comparison.The three important parameters that affect the stability of the bearing capacity are analyzed by finite element parameters: member slenderness ratio,section width-thickness ratio and geometric initial defects.The results show that when the slenderness ratio of the rectangular cross-section member with a cross-sectional form of 200×150×12 increases from 15.82 to 109.70,the stable bearing capacity decreases by74.3%;the slenderness ratio of the rectangular cross-section member with a cross-sectional form of 200×200×16 Increased from 12.41 to 86.08,the stable bearing capacity dropped by 66.7%.As the slenderness ratio increases,the final buckling mode of the component changes from local buckling to overall buckling.It shows that the slenderness ratio can significantly affect the final instability mode and stable bearing capacity of cold-formed thick-walled square rectangular cross-section axial compression members.At the same time,the width-to-thickness ratio of the section also has a greater impact on the final stable bearing capacity.For the rectangular section of 200×150 and the square section of 200×200,when the width-thickness ratio of the section changes from 10.5 to 18,the stability bearing capacity of the members with different slenderness ratios decreases by 37.46%～45.31%.In practice,under the condition of the same section size,thicker steel plates can be used to meet the requirements of higher stability bearing capacity.In actual engineering,under the condition of the same cross-sectional size,thicker steel plates can be used to meet the higher requirements of stable bearing capacity.For components with relatively small length and slenderness,local geometric initial defects have a greater impact on the stability of the bearing capacity.For components with relatively large length and slenderness,the initial defects of the overall geometry have a greater impact on the stability of the bearing capacity.As the initial defect amplitude changes from L/2000 to L/250(L represents the length of the specimen),the stable bearing capacity of the component can be reduced by up to 30.81%.In general,cold-formed thick-walled square rectangular cross-section axial compression components are still more sensitive to geometric initial defects.Comparing the experimental values,the calculated values of the finite element parameter analysis and the current domestic and foreign codes,it is found that the theoretical calculation values of Canadian and European codes are not safe.The Chinese codes and North American codes are generally safe,which verifies that my country The specification applies to coldformed thick-walled square rectangular cross-section axial compression components.In this paper,combining the results of experiments and parameter analysis,on the basis of previous studies,the Chinese code formula is revised,and the recommended formula for the stable bearing capacity of the cold-formed thick-walled square rectangular section axial compression member is proposed.The proposed calculation formula and parameter analysis The test results are in good agreement. |
