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Re: It's What You Don't Know That Hurts

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Bill,

I am assuming that the "U" beams are inverted "U's" and were pretensioned 
and used as spaced multi-beam units.  If they were pretensioned, then they 
probably have a lot of reserve concrete strength (P/T yards that I am 
familiar with try to work on a 3-day turn-around cycle), so external 
prestressing might be an option.  The downside to that is if they are 
inverted "U's", then they are highly susceptible to camber and without 
adjusting pavement thickness, there will be humpback after humpback.  (The 
camber in multi-beam inverted "U's" that I designed in the early '60's has 
grown to 3" or more in 60' spans.)

A modified external prestressing would be to use diaphragms as king posts or 
queen posts to relieve the load on the already installed P/S beams.

As George Reilly stated, there are a lot of options other than throwing away 
the existing beams.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

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