Research On The Theory For Overturning Calculation And Forensic Investigation Of Curved Girder Bridge Collapse

Curved girder bridge has been widely used in urban overpass,viaduct and ramp bridge of expressway because of its advantages.However,due to its spatial effect,the theory of structural deformation calculation under temperature and vehicle is relatively complex,which leads to the collapse or deflection accidents of curved girder bridge in service under the action of overload,temperature and centrifugal forces in recent years.Traditional overturning mechanism is mainly based on theory of rigid body,which simplifies it to rotate around a fixed axis.But the error is too large to satisfy actual overturning calculation.For curved girder bridge,precise overturning calculation theory cannot be solved efficiently due to bending-torsion coupling and large rotation.In this study,take the overturning accidents of two curved girder bridges and one linear girder bridge as example,and carried out the following four aspects of study.Firstly,with the work of forensic investigation at collapse site,possible failure modes of these collapses are systematically summarized.Corresponding criterion for overturning evaluation is then established.Next,considering the superposition of small rotation of deformable body and large rotation of rigid body about box girder,the spatial calculation theory of large rotation curved girder considering vertical flexural,radial bending and torsional deformation is established.Thirdly,the calculation theory is validated with measured field data of collapses and influencing factors of the theory are also analyzed.Finally,based on the systematic analysis of the wreckage at the collapse of Xiaoshan workers’ road ramp bridge,an accident investigation method based on contact pairs and collision trace of the wreckage to restore collapse process is proposed.This study indicates:(1)The anti-overturning of curved girder bridge mainly consists of three parts: rotation of deformed body of box girder under small deformation,the self-weight of box girder and the large rotation.The self-weight participate in the anti-overturning by bearing size or curve line,while the large rotation causes the redistribution of the reaction force of the torsional support at the end to indirectly resist overturning.(2)Our model considering the influence of self-weight with coupling of rigid-deformable body rotation can accurately calculate overturning bearing capacity of girder bridge.(3)In the investigation of bridge accident,combine contact pair of the wreckage with motion information observed by video,can better restore the collapse process.