Structural Behavior And Design Method For Lengthwise Steel-concrete Hybrid Beam Bridges

In the common three span prestressed concrete continuous beam bridge,the lengthwise hybrid beam bridge formed by replacing the concrete beam section of the middle span with steel can effectively reduce the self weight of the structure,increase the bridge span and improve the stress condition of the whole bridge,especially suitable for the bridge location with small side-to-middle span ratio,which has been more and more widely used in recent years.In this paper,the span layout,combined section stress and dynamic characteristics of the steelconcrete lengthwise htbrid girder bridge are studied respectively.The main research works and innovations are as follows:(1)The method of determining the span layout of the three-span longitudinal hybrid beam bridge and the reasonable length of the steel beam are proposed,and the analytical solutions of the internal forces and displacements of the three-span longitudinal hybrid beam bridge are derived.For the cantilever hybrid beam bridge,the criterion based on structural antioverturning stability and bending moment uniformity and the criterion based on deformation coordination at the suspension hole are proposed;for the continuous hybrid beam bridge,the criterion of equivalent section bending moment at the middle pier and simplified construction are proposed.After the process,the criterion that the structure does not appear negative reaction during construction and operation.(2)The research on the structure and force transmission mechanism of the steel-concrete joint section was carried out.The composition of the combined section and the role of each component are described.A finite element model is established for the combined section of the Qinhuai River Bridge,the second passage of Nanjing Airport.According to the force transmission ratio of the components,it is found that the force transmission efficiency of the shear connectors of each row is uneven.(3)The approximate analytical solution of the natural vibration frequency of the three-span longitudinal hybrid beam is derived and corrected.Further parametric analysis shows that when the mid-span concrete box girder occupies a relatively large amount,the assumed vibration mode function can better fit the actual vibration mode curve of the structure.The beam section is participating in free vibration.(4)The influence of total vehicle weight and vehicle speed on the mid span displacement response of the three span longitudinal hybrid beam and the change rule of impact coefficient with vehicle speed are analyzed.The research shows that the greater the speed is,the stronger the impact effect will be.