Elastoplastic Lateral Torsional Buckling Behavior Of Horizontally Curved I-Girders With Rectangular Concrete-Filled Tubular Flange

The steel-concrete composite girder bridge has outstanding technical and economic performance advantages,good social and environmental benefits.It conforms to the concept of green environmental protection and low-carbon,and has been vigorously developed in the process of transportation construction in China.In modern transportation systems,curved steelconcrete composite girder bridges are widely used.Before forming the composite section,the steel girder directly bears the load.Due to the non-collinear connection between the overall centroid and the bearing connection line,the curved girder bridge has typical bending-torsional coupling characteristics under vertical loads,which will aggravate the risk of bending-torsional buckling failure.Therefore,high requirements are put forward for the torsional stiffness of steel girders of composite section.Ordinary curved I-section steel girders are usually difficult to resist their own weight without temporary support,and are prone to instability during erection.Curved box-section steel girders are heavy,inconvenient to construct,and have obvious section distortion effect.The curved tubular flange girder has greater torsional stiffness and strength than the I-shaped curved steel beam,generates less deformation and stress during construction.And the weight is smaller than the curved box-section steel girders,making it easy to erect,therefore,it is more suitable for curved beam bridge systems.At present,numerical analysis methods are often used to study the mechanical properties of the curved tubular flange girder,and the mechanism of their lateral torsional buckling failure is not yet clear.Therefore,it is particularly important to systematic research the failure mechanism and mechanical response characteristics of curved tubular flange girders.This research has practical significance and value,which is conducive to promoting the construction of curved tubular flange girders bridges.In this thesis,the lateral-torsional buckling behaviour of horizontally curved rectangular tubular flange girder(CRTFG)was investigated.The top flange of CRTFG is rectangular concrete filled steel tube and the bottom flange is flat steel plate.The lateral-torsional buckling failure tests of three simply supported CRTFG and one simply supported curved I plate flange girder(CIPFG)under concentrated load at the mid span were developed.Finite element models of CRTFG were established,which were validated by experimental results.The parameters study of CRTFG using this finite element model,and the effects of flange geometric dimensions and material strength on the lateral-torsional buckling behaviour of CRTFG were analyzed.The ultimate lateral-torsional buckling bearing capacity of CRTFG with the central angle in the range of 0.05 to 0.4 rad is extended and calculated.A modified formula for calculating the ultimate lateral-torsional buckling bearing capacity of CRTFG is proposed,and its applicability is verified by experiments and finite element results.The research results indicate that:(1)the loading scheme and supporting device designed in this thesis are simple and effective,and can be used for experimental research on the lateraltorsional buckling behaviour of CRTFG.(2)The typical lateral-torsional buckling failure characteristics of CRTFG are obtained.At the initial stage of loading,CRTFG will simultaneously produce vertical,lateral displacement and cross section torsion.These deformations lead to second-order torsional effect under vertical load,which further aggravates the lateral-torsional buckling deformation of CRTFG.The larger deformation causes the lateraltorsional buckling failure of CRTFG,leading to a decrease in bearing capacity.(3)The smaller the curvature radius,the earlier CRTFG enters the elastic-plastic working stage,and the elasticplastic working stage is shorter compared to the entire loading stage.The length of the elasticplastic working stage of CRTFG and CIPFG with the same curvature radius is the same compared to the entire loading stage,but CIPFG begins to enter the elastic-plastic stage much earlier than CRTFG,and the ultimate load is also much smaller than CRTFG;(4)Parameter analysis shows that increasing the depth of the rectangular tubular flange appropriately is a more economical way to improve the ultimate lateral-torsional buckling bearing capacity of CRTFG.Compared to the change of the strength of filled concrete,the yield strength of steel has a more significant effect on the lateral-torsional buckling ultimate bearing capacity of CRTFG.(5)The modified formula of the CRTFG proposed in this thesis can be applied to calculation the ultimate lateral-torsional buckling bearing capacity of simply supported CRTFG under concentrated load at the mid span in the range of 0.05 ～ 0.4rad.