Application of Concordant Cables on Disposition of Prestressed Cables in Prestressed Concrete Continuous Beam Bridges
|School||Wuhan University of Technology|
|Course||Road and Railway Engineering|
|Keywords||Prestressed concrete continuous beams Secondary moments Concordant cables Linear transformation Prestressed steels area|
In recent dozens of years, with the flourishing development of transportation industry in our country, the prestressed concrete continuous beam bridge has become one of the most competitive bridge types, for its advantages including small distortion, large structure stiffness, and comfortable traveling. It is the dominant type among a large quantity of middle and short span bridges that exist in a broad area.This paper introduced the situation about the development of prestressed concrete continuous beam designs, and pointed the problem in designs. That is complicated design leading to unfeasible results due to secondary moments. So the application of concordant cables on design optimizing is promoted.This paper introduced the basic theories concerning the prestressed concrete continuous beam designs, including secondary moments, concordant cables, linear transformation, load equation, and three methods of getting concordant cable, which are moments diagram method, force method, and superposition method. It also analyzed equivalent loads produced by straight cables, folded cables, and curve cables. Three computing methods for secondary moments and effects on secondary moments by adjusting cables geometry parameters come from the reasons of generating secondary moments.It also illustrated the process to compute the prestressed steels area in detail, which is composed by gravity centerlines of steels, in the condition of least loads and greatest loads. Terms for feasible positions of the prestressed tendons and the way to satisfy them are proposed.In the designs of continuous beams, the section dimension, prestressed cable area and position arrangement are related with each other. The arrangement of the prestressed tendons in the continuous beams is more complicated than that in the simple-support beams. There are secondary moments due to superfluous restrictions in these in-determinate structures, and its impact on structures cannot be neglected. If the secondary moments could be utilized properly, a positive effect would appear definitely. Favorite prestressed tendon arrangement ought to produce an ideal concrete pressure line and satisfy other actual requests. The concordant cable is a way to arrange the prestressed tendons, which never generates secondary moments. It provides a convenient design method for engineers----first, getting a concordant cable position that can resist the outer moments, then coming out a linear transformation to get a feasible position when the first one is outside the beam. Therefore, searching of the concordant cables is becoming a helpful means to attain the purpose.Through an example, the moments of a six-span continuous beam under a condition of span-by-span construction are got by MIDAS program, and both maximum and minimum moments caused by dead loads and live loads for each section are gained. And prestressed steels area is obtained by moments computing. Basing on the concordant cables concept, prestressed tendons are laid in the prestressed steels area, and then economic and feasible steels arrangements are gained by linear transformation.