Span Railway Box Girder Bridge Dynamic Analysis Of Finite Element Method Based On Beam Segment

Box girders have been commonly used in all kinds of bridges. Due to the complicated deformation behavior of the box section under the loadings, the restrained torsion, distortion, plate local deformation and across diaphragms should be considered in order to accurately analyze the box-girder bridges. Beam segment finite element method is a superior method for the analysis of the static and dynamic behavior of box-girder bridges because it is able to consider all types of deformation of the box girder and the pre-stress influence. Taking a long-span railway pre-stressed continuous concrete box-girder bridge as a case study, this dissertation carries out the dynamic analysis of the bridge by using the beam segment element method as follows:1. Two new spatial displacement models of the beam segment element are conceived according to the element degree of freedoms of the box-girder bridge.2. The stiffness matrix and mass matrix of the beam segment element are derived accordingly where the cross diaphragms are included. Free vibration analysis has been carried out and both frequencies and mode shapes of the bridge are obtained.3. By using common finite element analysis software such as ANSYS and MIDAS/CIVIL, the dynamic properties of the same box-girder bridge have been investigated with both conventional beam finite element model and plate-shell finite element model. The Frequencies and mode shapes results are compared with those obtained from the beam segment finite element method. A good agreement has been found.4. The initial-stress stiffness matrix of the beam segment element is derived to which conveniently consider the pre-stress influence of the pre-stressed concrete box-girder bridges.5. Parametric study has been performed to demonstrate the influence of thickness and number of across diaphragms on the dynamic behavior of pre-stressed continuous concrete box-girder bridges and some significant conclusions are achieved.The results indicate that the beam segment finite element method has many advantages such as smaller element numbers and higher in the dynamic analysis of box-girder bridges. Furthermore, the beam segment finite element method is able to include the pre-stress, across diaphragm, restrained torsion, distortion, plate local deformation. Therefore, it is expected that the beam segment finite element method can be an effective approach for the further dynamic response analysis of the pre-stressed concrete box-girder bridge under earthquake, wind and vehicle loadings.