| In recent years,with the concept of "prefabricated construction" is put forward,steel structure has been developing rapidly in the construction industry.Compared with hot-rolled steel,cold-formed thin-walled steel has the characteristics of light weight,diversified crosssection and cold-formed effect,which has huge application value.Above all,a new type of cold-formed thin-walled steel frame structures with built-up sections was structured with the use for reference from the traditional steel frame structures and the light-gauge steel system.On this basis,a closed cross section of built-up multi-roll column suitable for the system was put forward.And the section optimization was performed with the finite strip software of CUFSM.Then,failure tests and numerical analysis were conducted on built-up multi-roll lipped channel columns.And this thesis performed parametric finite element analysis on the key factors about slenderness ratio,width-thickness ratio,bolt spacing and eccentric state,which may affect the buckling behavior of columns.At last,the direct strength equation for built-up cold-formed multi-roll columns undergoing the buckling bearing capacity was given.Through the above research,the main conclusions are as follows:(1)The built-up multi-roll lipped channel column is made up of four identical cold-formed thin-walled steel column limbs,which are connected with high-strength bolts.And the optimized column with the finite strip software of CUFSM has excellent resistance to local buckling and distortional buckling,which is suitable for use in multi-story frame housing.(2)The test turned out that the eccentric direction and eccentricity had great influence on the mechanical behavior of the specimens.More specifically,when the eccentricity is on the weak axis,the specimen failed with the partial crushing,without the global buckling,otherwise,the specimen failed with the global buckling.There is no obvious local buckling of the plate buckling of the column except for the failure section.(3)The key factors about slenderness ratio,width-thickness ratio,bolt spacing and eccentric state,have the great influence on the buckling mode,initial stiffness and ultimate bearing capacity of the columns.More specifically,the cross-section utilization ratio of column increases with the decrease of width-thickness ratio,which up to the maximum with widththickness ratio of the panel is in the range of 21.1 to 25.0.Compared with the fully closed section,the greater the spacing between the bolts,the more the ultimate bearing capacity is reduced.For the bearing capacity of the axial compression column,the correction coefficient ? related to the bolt gap and slenderness is proposed.And the ultimate bearing capacity of the column decreases with increasing eccentricity,and increases with the increase of eccentric angle.(4)For the axial compressed built-up multi-roll lipped channel columns in the common range,the direct strength method equation in the North American Code(AISI S100-2012)is not safe for the calculation of the global buckling bearing capacity,and the correction coefficient ? is proposed.For the bending columns,the equation of the direct strength method in the Code is in good agreement with the actual global buckling bearing capacity when the bolt gap is 500 mm,and does not require correction.Based on this,the correction coefficients ?x and ?y related to bolt gap are proposed for the bending capacity around the strong axis,weak axis respectively.(5)For the local buckling capacity about built-up multi-roll lipped channel columns,the North American Code(AISI S100-2012)has a large deviation from the actual calculation results,and the equation values are very conservative.Based on the analysis results,the direct strength equation for built-up multi-roll lipped channel columns with axial compression and eccentric compression state undergoing buckling bearing capacity were fitted.The fitted equation was testified against the test rusults and finite element analysis results and yielded good agreement. |
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