Study on the Buckling Stability of TPZ/48 Steel Box Girder Type Bridge Erection Machine under Construction State

An elastoplastic finite element model was established by finite element software ANSYS for a steel box girder type bridge erection machine with long span under pouring construction state.Based on nonlinear buckling theory,displacement controlled arc-length method was adopted to load and track the equilibrium path of structure.Nonlinear buckling analysis was carried out on the structure of bridge girder erection machine with initial geometric imperfection.The ultimate bearing capacity as well the safety factors of local and overall stability of this type of bridge girder erection machine under construction state were determine through analyzing the load-displacement curves of the instability characteristic points.The ultimate bearing capacity of the bridge girder erection machine was 3 755 t,which was greater than the designed construction load 1 600 t.The safety factor of overall stability was 2.35,while that of the local stability was only 1.32.The instability occurred at the bearings,floor,diaphragm and webs of the midspan.The analysis results of nonlinear buckling and eigenvalue buckling were compared and analyzed.Results show that for complex structure,the critical load got by nonlinear buckling analysis may be greater than that got by eigenvalue buckling analysis,for the reason that after buckling happened on the local position in the structure,the load would be transferred,and the structure would still retain the overall bearing capacity.