The Design of Modern Steel Bridges - TEDI

20 The Design of Modern Steel Bridges
Substantial movements in wind were previously found in the 2300 ft (701 m)
span Bronx Whitestone Bridge, which had a 74 ft (23 m) wide deck, and also in
the Golden Gate Bridge, and diagonal stays between the cable and the deck and
additional lateral bracing in the deck structure had to be provided. A chain pier
at Brighton, England, had collapsed in a storm several years earlier.
The positive outcome of the Tacoma disaster was the extensive wind tunnel
testing of scaled models and aerodynamic analysis of various deck shapes in all
wind speeds. This practice re-established long-span construction on a firmer
basis, leading not only to the reconstruction of the Tacoma Bridge in 1950 with
a wider 60 ft (18.3 m) deck with 33 ft (10 m) deep stiffening trusses, but several
more such bridges were built, e.g. Mackinac Bridge in Michigan in 1957 with
3800 ft (1159 m) span, designed by David Steinmann, and finally in 1965 the
4260 ft span (1298 m) Verrazano Narrows Bridge across the New York harbour
entrance, designed by Ammann, which just exceeded the then longest span
length of the Golden Gate Bridge. Steinmann introduced the concept of leaving
slots in the deck, so that wind vortices escape upwards from underneath, thus
setting up turbulence and thereby reducing the rhythmic up and down forces on
the deck.
In Europe, Tancarville Bridge over the Seine at Le Havre with a main span
of 610 m (2000 ft) was completed in 1959. The non-American features of
Tancarville Bridge were the concrete towers and the continuity of the stiffening
girder between the main and the side spans. This was followed in 1964 by
the huge bridge over the Tagus at Lisbon with a central span of 1013 m
(3323 ft) and almost at the same time the Forth Road Bridge near Edinburgh
Figure 1.19 Forth Road Bridge, Scotland (1964).