A Novel Approach to Prestressed Concrete Bridge Design

C.J. Burgoyne and J. Sundaram

Engineering Department, University of Cambridge, Cambridge, UK

Design of prestressed concrete bridges is normally performed through an iterative process of generation, evaluation and modification of trial designs. The presence of secondary moments in continuous structures and the effects of concrete creep in segmental construction, complicate the design task. Inexperienced designers often find themselves carrying out an endless repetitive search for a feasible solution. The paper describes a technique which helps carry out design, not by repeated alterations to the chosen trial section and cable geometries, but by evolving the solution as the design proceeds. The design is carried out in modules with decisions on the parameters taken sequentially. The method has been implemented in an expert system, although it is equally applicable to more conventional design approaches.

The paper presents an approach to prestressed concrete bridge design, to guide engineers to arrive at good design solutions, without the necessity for redesign. The major design constraints were identified and suitably incorporated in the design approach, so that subsequent design decisions taken would satisfy all these constraints. Why deal with prestressed concrete bridge design principles? Bridge design is one of the most complex tasks posed to designers because of the large number of design parameters involved, and their complex interactions. The analysis of prestressed concrete structures is well understood. However, there are hardly any text-books or research papers which cover the design aspects, especially for complex structures like bridges. The lack of design knowledge makes the iterative process tedious, and calls for a better understanding of the design principles.

The paper illustrates that good design methods could be developed by a careful study of the design process and the associated intricacies. By taking account of governing parameters and the factors affecting design early in the design process, the approach adopted ensures that the whole design evolves in a logical sequence, without the need for redesign, Most of the above principles, although described here for bridge design, could be extended to outer prestressed concrete structures.

References

Burgoyne, C. J., 1988, Proc. Instn. Civil Engineers 85, 161.

Burgoyne, C. J., 1988, Proc. Instn. Civil Engineers 85, 333.

Burgoyne. CJ., and Jayasinghe, M.T.R., 1993 "Rationalization of spine beam design for expert systems", FIP 93 Symposium, Kyoto, Japan.

Low. A. M., 1982, Proc. Instn. Civil Engineers 73, 351.

England. G.L., 1991 "Creep behaviour of prestressed concrete structures", A four-day advanced course on "Design and analysis of prestressed concrete structures", Cambridge.