:: o answer #2, a single car, or even pedestrian traffic may be the
:: limit,
:: or could be in the 100's of tons range. The full range. I drove a
:: Ford
:: Bronco SUV with the family, weight right a 3 tons across the Royal
:: Gorge
:: Bridge (highest suspension bridge in the USA - google for it),with
:: a 3
:: ton limit. There was considerable pedestrian traffic. As we
:: approached,
:: the foot traffic scattered quickly. We were really rocking the
:: bridge!! :)

In London (UK) there is Battersea Bridge, which is basically made of 
wood - whilst cars streem over it into and out of London (used to be 
time of day directional) the horseguards (their barracks used to be 
just down the road in Chelsea), would have to dismount to cross the 
bridge. The vibrations caused by a 20 odd horses trotting over the 
bridge managed to be at the right natural oscillation frequency and 
the bridge was in danger of falling down, but a a 10 ton truck roaring 
over no problem.

Colin 
--
cdb, colin@btech-online.co.uk on 4/07/2009
 
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