Research On Overall Stability Of Beams With Semi-rigid Connections

The steel beams without intermediate lateral restraints within their length are prone to flexural-torsional buckling.The support condition of beam is an important factor affecting the overall stability bearing capacity of steel beams.Most researches focused on the simply beams,which has the advantages of simple mechanical model and analysis.In Chinese Standard for design of steel structures(GB 50017-2017),only the deign formulas on overall stability for simply beams subjected to equal end moments or transverse load are provided,while the consideration of end constraints is lacked.A beam-column joint of steel frame structure is usually semi-rigid joint between ideal hinged joint and rigid joint.It makes the constraint conditions of the beam end more complicated,and results in a big difference from the traditional calculation model of simply beams.Therefore,the calculation method for the overall stability bearing capacity of semi-rigid connected I-beam was deduced in this thesis.And the corresponding design formulas were put forward,which provide some supplement for the current steel structures standard.Firstly,the calculation method for the overall stability of beams was analyzed,and the total potential energy equation of flexural-torsional buckling was determined.The end restraints were considered as spring constraints.Then the total potential energy equation of flexural-torsional buckling for semi-rigid connected beam was established.The elastic critical moment formulas for fixed-ends doubly symmetric I-beam were obtained by energy method,which could be used as the reference for semi-rigid connected beam.Taking semi-rigid end-plate connections as the objects,the lateral bending restraint and in-plane rotation restraint at both ends were considered as springs.Then the elastic critical moment formulas for semi-rigid connected I-beam were deduced,and the moment coefficients of load type and load height were obtained.The joint stiffness of semi-rigid end-plate connections were analyzed by finite element software ABAQUS,and the buckling analysis for steel beams with different constraints was carried out as well.The calculation results of the method in this thesis were in good agreement with the finite element analysis results when the equal end moments located on shear centre.For the case of transverse load acting on the upper flange,the theoretical results and the finite element results were analyzed and discussed.The cause of error was analyzed,and the correction method was put forward and verified by examples.At last,the design formulas on elastic overall stability for semi-rigid connected I-beam were put forward.The simple formulas for the equivalent moment coefficient of two special supporting cases were obtained by means of regression analysis.The calculation method in this thesis was compared with foreign codes through examples,and the results showed that the proposed method for beams with end restrains has good applicability.