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Long Span Bridge - Any Thoughts Out Ther

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AASHTO Bridge Specs, 15th Edition, Introduction, page v, states:

"Primarily, the specifications set forth minimum requirements which are 
consistent with current practice, and certain modifications may be necessary 
to suite (sic.) local conditions.  They apply to ordinary highway bridges and 
supplemental specifications may be required for unusual types and for bridges 
with spans longer than 500 feet."

E & O insurance applications that I have seen typically ask if you do bridges 
longer than 300 ft, but does not indicate whether they are thinking of ten 30 
ft spans or one 300 ft span.

So, probably something with spans between 300 ft and 500 ft could be 
considered a long span bridge, and everything with spans greater than 500 ft 
would be a long span bridge.

I would suggest that any bridge with a span 25 percent greater than you have 
ever designed before should be designed with the care that you would take if 
you designed a "long span" bridge.

Hope this helps.

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

Robert Rogers wrote:

>>Talk about a silent world ......

Well let me throw something back out here for discussion.  Let's dissect the
word "long span".  Of the three bridge types (span, arch, and suspension) a
span bridge is classically defined as:

        "A structure supported on each end by a foundation"

I don't necessarily believe that the span needs to be continuous to be
considered long.  Since we now have defined what a "span" type of bridge is,
what constitutes long ?

Is this a relative term ?  The 1981 article "Recommended Design Load for
Bridges" in the Journal of the Structural Division contains a small hint at
what defines "long span".  Under its discussion for traffic loading for long
span bridges it states:

        "This section applies to any bridge or component of a bridge that is
outside the     ranges of the code which would normally be appropriate for a
shorter bridge at       the same location."

How's that for vague ?  If I have a 420' simple span Pratt truss bridge is
that a long span bridge ?  Let's here some chatter out there.  What are your
thoughts ?


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>I am currently in the midst of a philosophical debate with a fellow
engineer
>on the definition of what a constitutes a "long span" bridge.  We both have
>some differences in interpretation and cannot find an AASHTO definition
>thereof.  I have also search a couple of definitive references (by
>Xanthakos) with no luck.  Anybody out there who can point me to a source
>(AASHTO reference, Classical Text Book, etc.) that defines this term ?  Or
>if you can E-Mail or fax me (937-461-0743) a copy of the definition that
>would be tremendous.

>Thanks in advance.<<