Civil Engineering Reference
In-Depth Information
been more rational to have adopted a single plane of stays rather than the two planes
shown.
c) Solid slab decks
Another way forwards for concrete decks has been given by R. Walther who has built
a cable-stayed deck that consists of a solid concrete slab. The Diepoldsau Bridge has
a 97 m main span, and an overall width of 14.5 m [2]. The two planes of stays are
anchored close to the edges of the deck that is 550 mm thick at the centre, thinning
to 360 mm at the edges, with an average thickness of 490 mm , which is similar to
the average thickness of more conventional beam and slab or box section decks, but
without the complications.
This is a very economical concept, and appears to offer clues to the best way forwards
for narrow decks with spans up to at least 300 m. However, it needs proving that such
thin decks are not at risk of buckling under the compression of the stays. Intuitively,
it appears likely that such a deck will have a great resistance to buckling, as vertical
displacement is inhibited by the stays which act as vertical springs. Clearly, the stays
must be close enough to inhibit local buckling between their points of attachment.
A scale model was tested at the Swiss Federal Institute of Technology in Lausanne,
representing at 1/20 scale a 200 m main span bridge, with a 14 m wide, 500 mm thick
slab deck, with stays spaced at 6.4 m along the deck [3]. The deck thickness was thus
1/400 of the span. This test concluded that yielding of the stays would occur before
the deck became unstable.
Figure 18.13
Proposed coffered deck
