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Re: Pedestrian Bridge Bearings

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Michael,

	By all means FASTEN IT!  Even loosely.

	We had a two span continuous LRT (rapid transit system) bridge in
Calgary which, prior to being in service slid off its supports and into
the river up side down.  As I understand it, thermal effects caused to
structure to behave like a bimetal strip and lift one end above the
restraining pins following which it slid off the foundation.  For the
cost of a dozen nuts this failure could have been prevented.

				Regards,

				H. Daryl Richardson

Michael Hemstad wrote:
>
> Daryl,
> Thanks for your reply.  My concern with the
> elastomeric bearing at the end span is that the
> combination of light dead load and steel surface makes
> me think it will walk if I don't somehow fasten it to
> the beam.  You asked a good question, to wit:
>
> >As a matter of curiosity, why would you use one
> >continuous two span
> >structure rather than two simple span structures?
> >The savings in
> >erection using two simple spans would seem to me to
> >more than outweigh
> >the material saved using a continuous structure.
>
> >                               Regards,
>
> >                               H. Daryl Richardson
>
> I think (hope) it's about a horse apiece.  There will
> be a field splice, obviously, but it's not too
> complicated.  The spans are unbalanced:  122 feet and
> 70 feet, give or take, with an 18 foot cantilever
> reaching out to the existing structure.  I had a long
> talk with the fabricator, and he indicated he would
> rather build the field splice than try to ship a 122
> foot piece down the road.  (Of course, he's not
> erecting it.)  The splice enables us to make the field
> pieces about the same, and still ship just two pieces,
> which represented a cost savings to him.  The short
> span will be erected first.  I haven't completed my
> analysis, but I'm guessing I'll have to hold the short
> end down.
>
> Mike Hemstad
> TKDA
> St. Paul, Minnesota
>
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