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RE: Wide Bridges - Longitudinal Joint

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Caltrans limits the width of decks to 80 feet in their "Memos-to-designers".
This does not appear to be followed as a rule, however, as I am familiar
with a couple of (approx) 160' wide decks on Caltrans bridges.  

I think the limit may be on what size "bidwell" the local contractors have
available, so you might check with them.

-----Original Message-----
From: Larry Sandhaas [mailto:lws(--nospam--at)netexpress.net]
Sent: December 21, 2000 5:29 PM
To: seaint(--nospam--at)seaint.org
Subject: Wide Bridges - Longitudinal Joint


Something of an introduction by a new list member. 
I am a structural engineer working mostly on bridge work 
in the upper Midwest - Iowa and Illinois.

Single Point Interchanges seem to have gained popularity -
especially in the south and west, but to a lesser degree
in the my part of the country.  Why this is, I am not sure.
The DOT's seem to be rather conservative in these parts.
The single point popularity stems from the lesser
land area required when compared to the conventional 
cloverleaf interchange.  The price paid is rather wide
bridges to accomodate ramps and turning lanes.

I have learned from my company's other offices in the west
that wide bridges - say between 150'-250' edge to edge-
have been built without a longitudinal expansion joint.
I have copies of plans of a bridge in Omaha built in just
this fashion. No longitudinal joint, integral abutments 
and reasonable amounts of transverse deck reinforcement.
Obvious maintenance advantages - I hate deck joints.
I've been thru too many inspections and replacements
of old failed deck joints.

Iowa and Illinois DOT policy precludes construction of 
bridge decks greater than about 100' wide without the longitudinal
joint.  Great efforts in design have been made to accomodate
this policy for many years.

Simple question - how is it that other states can build bridges
quite wide with what appears to be ordinary flexural reinforcement?
I think I know the answer - much of it having to do with traditonal
ways of doing things.  I've done some "back of the envelope"
finite elements to satisfy curiosity, and I can't find any 
substantial difference between a 100' wide bridge and a 200'
wide bridge subjected to transverse temp. strains and full restraint
at abutments.

What measures are taken in other states to accomodate the building
of very wide bridge decks, or similar structures in general?
I have a suspect that initial shrinkage stresses could be more
of a problem than temperature long term.  This could be addressed
with a prudent choice of deck pouring sequence.

Any comments welcome-
Regards-
Larry Sandhaas, PE