A Timoshenko beam finite element formulation for thin-walled box girder considering inelastic buckling

A Timoshenko beam finite element model is formulated based on the Lagrange and Hermitian interpolations, in which the transverse shear deformation is explicitly evaluated. To account for the local inelastic buckling, the finite element formulation is coupled with a Smith-type progressive collapse method where the nonlinear responses of local structural members can be assessed. The effect of shear lag is accounted by an effective breadth theory. This coupled model enables an efficient prediction of the flexural behaviour of a thin-walled box girder under lateral loading. To demonstrate its capability, a case study is completed on a single-skin box girder under four-point bending. Equivalent finite shell element analysis is carried out for validation. The proposed method shows a close correlation with the shell element model in both strength and stiffness predictions. It is found that the effect of shear lag is significant in this case study, which substantially reduces the stiffness of the box girder.