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Re: modeling of elastomeric bearing

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I've always broken down a bridge into its various parts.

For the Superstructure, I imagine you're using steel due to the curvature...

I've used two different software packages for curved girders.. MDX and DESCUS.
I don't have a preference one over the other.

>From these, I design my girders.  Then I design the Deck. 
The software gives me reactions to designt the bearings and the substructure.
Keep in mind that if you have a very large skew and long span lengths, elastomric
bearings may not be the best alternative.  You also might run into problems with
what your local DOT considers acceptable.

Generally with Curved girders, you're not going to use square elastomeric bearings.
You're going to use pot bearings, some will be guided, and some will be
non-directional.  VDOT has a method where you assume a point of expansion,
place a fixed bearing at that point, and fix a couple of bearings at each pier/abutment.
The rest are non-directional and free to expand wherever they want to.  DSBrown
is the major vendor of pot bearings.

Expansion Joints are generally dictated by the geometry of the bridge. I.E for
X number of Feet/Meters, your bridge is going to expand Y inches/centimeters.
Then it becomes a process of selecting a joint system that will accomodate the
movement dictated by the geometry of the superstructure and incorporating the
details into the overall bridge geometry.

With a curved bridge, you're going to find that the beams are subject to torsional
loadings.  The outside beams will have more stress than the inside beams, and
therefore your bearings and substructure will be designed to handle the forces that
come to them.

The last curved structure I worked on framed into integral box-beam cross girders.
Even taking into account the rotational and vertical stiffness of the cross girders,
the stress in the superstructure was only 3% different from assuming continuous 
curved girders and a normal superstructure.  So If you really want the quickest 
way to do it, I'd design the superstructure for 24KSI in ASD or 45 KSI in LFD.
I haven't used LRFD yet.

Good Luck!

Jonathan Mallard

Jonathan Mallard
Ralph Whitehead Assoc.
553 Southlake Blvd.
Richmond, VA 23236
(804) 794-1185
(804) 378-0923 FAX