Recent evolution of cable-stayed bridges
Introduction
Engineers invented the concept of cable-stayed bridges very early on, at the same time as they began developing suspension bridges; however, with the collapse of the bridges built over the rivers Tweed and Saale, at the beginning of the 19th century, the idea was abandoned. Roebling and others later introduced some cable-stays in suspension bridges to reduce deformability, such as for the Brooklyn bridge, and some innovative suspension systems very close to those of cable-stayed bridges were invented, such as those by Gisclard.
Surprisingly, the first “modern” cable-stayed bridges were built in concrete by Eduardo Torroja in the 1920s (Tampul aqueduct) and by Albert Caquot in 1952 (Donzère canal bridge; Fig. 1); but the real development came from Germany with papers published by Franz Dischinger and with the famous series of steel bridges crossing the river Rhine.
The international development of this bridge type began in the 1970s, but a very big step forward took place in the 1990s, when cable-stayed bridges entered the domain of very long spans which was previously reserved for suspension bridges 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. It is extremely interesting to analyse the progress in the world record for cable-stayed bridges, since it provides keys to understand the evolution of their design.
However, other aspects of the design of cable-stayed bridges are worth discussion: the development of slender decks for medium and large spans; the concept of “extradossed” bridges, considered as an intermediate solution between concrete box-girders prestressed by external tendons and cable-stayed bridges; and the design of multispan cable-stayed bridges.
Finally, we shall return to the very long spans and their limits, predominantly controlled by the dynamic response to turbulent wind; not forgetting the cable-vibrations, the control of which now appears to be one of the major problems in cable-stayed bridges.
Section snippets
New record spans
The world record for cable-stayed bridges progressed very slowly in the 1970s and 1980s, but since the beginning of the 1990s all records have been broken in a gigantic step forward (Fig. 2):
the Saint-Nazaire Bridge in France (404 m in 1975), with an orthotropic box-girder for the deck (Fig. 3);
the Barrios de Luna Bridge-also called the Fernandez Casado Bridge-in Spain (430 m in 1983), in prestressed concrete (Fig. 4);
the Alex Frazer Bridge-also called the Anacis Island Bridge-in Vancouver,
Slender decks
Recent years also show the evolution towards slender and flexible decks for medium spans:
Composite decks, with two steel I-shaped beams of limited depth, even for rather long spans, up to 602 m for the Yangpu Bridge. Limits only arise with aeroelastic stability, due to the rather unfavourable shape of the deck which calls for some aerodynamic amendments (fairings on both sides to give some streamlining; baffles between the main beams to divide the open void below the deck and limit torsional
Extradossed bridges
Since the allowable stress in cable-stays is rather low (generally between 40 and 45% of the Guaranteed Ultimate Tensile Stress, GUTS, for the Service Limit States), as compared with tendons (between 60 and 72% of GUTS, to give an idea, depending on code specifications and prestressing losses), some engineers imagined solutions where cable-stays could be replaced by tendons.
The pioneer bridge is the famous Ganter Bridge designed by Christian Menn. The concrete box-girder is “stayed” by
Multiple cable-stayed spans
Finally, a very recent trend must be mentioned: the design of multiple cable-stayed spans.
The pioneer construction is evidently the Maracaibo Bridge designed by Ricardo Morandi. The structural concept is clear: a series of extremely rigid pylons—prestressed concrete trusses—support cable-stayed cantilevers with a simple span suspended between two successive pylons (Fig. 25Fig. 26Fig. 27).
This static system was reproduced by Morandi with a unique main span for two bridges in Italy and for the
Dynamic response in turbulent wind
Very long cable-stayed spans are controlled by their aerodynamic behaviour which classically has three different aspects: the effects of vortex shedding; aerodynamic stability; and the dynamic response to turbulent wind.
The orientation towards streamlined box-girder sections inspired from the English suspension bridges, and with two lateral planes of cable-stays, practically solves the problems related to vortex shedding and aerodynamic stability.
For the Normandie Bridge, for example, vortex
Cable vibration
Many cable-stayed bridges had to suffer important cable vibrations, beginning with some of the early German bridges and with the Brotonne Bridge in 1977. Unfortunately, owners, designers and contractors generally hide these problems and engineers had to wait years before they could begin to understand and solve them.
It should be stated that many factors can produce cable vibrations. We cannot detail them here, but only give a general view of the possible phenomena.
The first one is classical:
Conclusion
The evolution of cable-stayed bridges is proceeding rapidly in many different directions: the development of slender and flexible decks which open many possibilities for medium spans, including competition with other bridge types; the application of cable-stayed bridges to multiple spans, which will certainly have some importance for large projects; and, of course, the rapid increase in span length, in competition with suspension bridges. However, in this last domain, the condition is a
References (12)
- Walther R, Houriet B, Isler W, Moı̈a P. Ponts haubanés. Lausanne: Presses Polytechniques Romandes,...
- Podolny W, Scalzi JB. Construction and design of cable-stayed bridges. New York: John Wiley,...
- Troitsky MS. Cable-stayed bridges. Oxford: BSP Professional Books,...
- Gimsing NJ. Cable-supported bridges. Chichester: John Wiley,...
- Cable-stayed bridges. Experience and practice. In: Kanok N, editor. Proceedings of the International Conference on...
- Seminar on cable-stayed bridges. Proceedings of the Seminar organized by the Indian group of IABSE. Bangalore, October,...