Theoretical Research On Torsion And Flexural-torsion Buckling Of Thin-walled Box Beam With Concrete-filled Steel Tube Flanges

The concrete-filled steel tube structures have the advantages of high strength and good ductility and simple construction,which have been widely used in engineering practice at home and abroad.The thin-walled box beam with concrete-filled steel tube flanges is a new type of architectural structure.The box beam has high bending rigidity and high torsional rigidity,which can improve the strength and the stability outside the plane of the component.In addition,concrete-filled steel tube as the flange of box beam,the material can effectively reduce the height and the high-thick ratio of the web,and improve the shear resistance of the structure.The thin-walled box beams with concrete-filled steel tube flanges can be regarded as a combination of closed-closed-solid components in form.During the use of a building,due to the variability of the living load of the structure,the thin-walled box beam will bear the role of eccentric load.Therefore,in the process of designing and using of the structure,we should consider both the bending and torsion of the thin-walled box beam.Compared with bending problem,the torsion problem of thin-walled box beam is a more complex mechanical problem.The existing theories on torsion and flexural-torsion buckling of concrete-filled steel tube flanges thin-walled box beam.Solving the torsion problem is very important for the contemporary construction industry.Based on the theory of the combination torsion of closed thin-walled component in plate-beam theory written by Professor Zhang Wen-Fu,this paper studies the theory of torsion and flexural-torsion buckling of concrete-filled steel tube flanges thin-walled box beam.And using the finite element software ANSYS to verify the correctness of the theoretical derivation.The main research contents of this paper are as follows:(1)Based on plate-beam theory and continuum model,the torsion problem of concrete-filled steel tube flanges thin-walled box beam is theoretically deduced and analyzed,and the total strain energy and the expressions of free torsion stiffness and restraint torsion stiffness are given.(2)Taking the cantilever beam as an example,the energy variational model and differential equation model of concrete-filled steel tube combination flanges thin-walled box beam torsion are established,and the torsion angle expression and theoretical analysis of the maximum torsion angle are given.(3)By changing length and cross-sectional size of the beam,12 different box beams were selected,and the model was established by ANSYS.To extract the maximum torsion angle(the free end torsion angle)in the form of cantilever beam and compared with the theoretical analysis solution,which verifies the correctness of the theoretical analytical solution.(4)Based on plate-beam theory and continuum model,the flexural-torsion buckling problem of concrete-filled steel tube flanges thin-walled box beam is theoretically deduced and analyzed,and the expressions of total strain energy and total initial stress potential energy and total potential energy are given.(5)Taking the simple beam as an example,the energy variational model and differential equation model of concrete-filled steel tube flanges thin-walled box beam flexural-torsion buckling are established,and the critical moment calculation formula for box beam are given.(6)By changing length and cross-sectional size of the beam,12 different box beams were selected,and the model was established by ANSYS.To analyze the model and extract the critical load in the form of simple beam.To compared with the theoretical analysis solution,which show that the critical moment calculation formula is reasonable.