The Optimization Design On Superstructure Of Standard Span Beam-Bridge

In the past, the goal of optimum design is to get low cost and reduce material when bearing capacity of single-beam is satisfied. However, sectional dimension is so lower that bridges can't satisfy traffic rising and make a lot of incipient faults. Under present social economic condition, bridge design should satisfy criterions of design load and increase bearing capacity in order to strengthen service performance. These are contents of bridge structural optimization.Diseases in superstructure make the life-span of bridges shortened. In allusion to this problem, detailed investigations were made in this article. On the base of these data, we analyze reasons of scathes of bridges. Local damage of bridges is much serious. Reasons: firstly, sectional dimension is so little that torsional stiffness of single-beam isn't enough. Secondly , protective layer thickness is too thin to protect concrete reinforced bar and reduce durability. Lastly, each main beam is joined by cross girder and the more rigid of cross girder the more entirety of bridge. But from investigation we can see that the fact isn't perfect. It is necessary that we find a method which can exploit the particular advantages and weaken the shortages of reinforced concrete. From data reports we can see that bridge designers emphasize resistance to bending and shear that was studied sophisticatedly, but many experts neglect resistance to torsion. Existing investigation state of bridges shows that diseases of bridges designed under the theory are exposed. So we should take care of resistance to torsion.There are many cross-section forms such as T cross-section, I cross-section, slab cross-section, box cross-section etc. for common span of bridges. Slab and box cross-section beam's resistance to torsion is stronger than T and I cross-section beam's. But deadweight of slab and box cross-section beam is bigger than it of T and I cross-section beam. Taking advantage of both, this paper choose T cross-section and enlarge detail dimension. The goal of optimum design is to increase torsion inertia moment and reduce shearing stress when moment of flexion and shear bearing capacity of single-beam is satisfied. In allusion to section modality and transverse joint of common span bridges, we choose two kinds of calculating theories in transverse distributing calculate process: the theory of rigidity crossbeam and the theory of hinged girder and slab. Making the use of the theory of optimized design, I constitute mathematics model and choose appropriate calculated method. And find the form and detaildimension of section when beams of the bridge satisfy bending moment^ shearing force and torsional moment. Because width of rib is larger than before, we can change single-rib beam to double-rib beam. Stability in transportation and aethetic effectiveness is improved. In this article we make the example of 20m-span simple-supported reinforced concrete beam-bridge. Compared with existing state about bridges, the latter is more safety than the former when we calculate resistance to torsion.