Comparison

Because wire stay cables are generally prefabricated and strand stay cables are more commonly assembled on site using a strand-by-strand installation method, the choice of the suitable cable system for a particular project depends on many factors:

It has often been considered that prefabricated wire cables are best suited to smaller bridges or those with very long spans. On site fabricated strand stay cables are usually suited to intermediate range spans. However, the designer, together with the specialist stay cable company, should evaluate each project individually, taking structural capacity and the global interaction between cables and the structure into account. Erection requirements as well as the overall economics and availability of the various systems should also be considered.

Cable Vibration

Despite the wide use of cable-stayed bridges, there are still several areas of great concern, especially the effects and elimination of cable vibration phenomena. Even newly constructed cable stayed bridges have experienced quite severe vibrations which may result in failures of cables [4].

Several cable vibration mechanisms have been identified and characterized with the four most common phenomena: vortex shedding, galloping, parametric excitation (deck/pylon and cable interaction), and wind and rain induced vibrations. Excitation mechanisms and preventative design measures are a popular topic in the literature [5, 6, 7, 8, 9, 10, 11]. Additional information on effective countermeasure against cable vibration can be found here…

Future Developments

Storchenbrücke
Switzerland (1996)

 

Both wire and strand type cable systems are today’s solutions of choice for modern cable-stayed structures. Over the years, the ultimate tensile strength of the wires and strands has gradually been increased and will be further increased. Furthermore, the corrosion protection systems have been enhanced. Whereas grout was a widely used corrosion protection system for many years, today’s stay cables employ grease and wax as the primary filler. Although poor or faulty grouting can result in poor performance of the cables, there are many examples of grouted stay cables which have been inspected and found to be in perfect condition. To enhance the long term durability of the stay cables, the use of epoxy coated strands, as well as the injection of the stay pipe with gas to prevent corrosion are more recent developments and potential alternatives for the future.

Engineered in collaboration between EMPA and BBR, the Storchenbridge in Winterthur (Switzerland), crossing the major east-to-west axis of the Swiss Federal Railway Network, was the world’s first bridge to use carbon stay cable technology. Due to its low self-weight, carbon stay cables are a promising solution for ultra long span bridges. Their extremely high fatigue resistance and the fact that carbon is non-corrosive are further advantages of this type of cable. It should be noted that special care should be taken when choosing an anchorage system for carbon stay cables.

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