Return to index: [Subject] [Thread] [Date] [Author]

QUERY: Bridge Bent - Braced or Unbraced?

[Subject Prev][Subject Next][Thread Prev][Thread Next]
This should seem obvious, but I'm actually "swayed" both ways on this (a little
lateral stability humor there).

I have a bridge bent, a typical plane frame consisting of a R/C cap beam on four
large circular R/C columns. The foundation is a drilled shaft for each column.

This is a pier support for a three-span continuous steel plate girder highway
bridge (R/C slab on beams).

Now, this particular bent has "fixed" bridge bearings, and the other piers in
this unit are expansion bearings. The bearings are the composite
elastomeric/steel shoe type, so there is definitely some limited play.

Now, even though the bridge can "move" it can do so of course only in a limited
fashion.

What I'm wondering is: Is this frame braced in both the in-plane and
out-of-plane directions because of this superstructure?

A highway bridge of this type has large theoretical lateral forces (in the
out-of-plane direction of course) from vehicle breaking, such that you get a
calculated displacement of 10 inches due to those forces. Obviously, the bridge
isn't going there, so the top of the piers aren't either.

I suppose I could just set a displacement of 3 inches (the "gap" between the
bridge unit and the back of the abutment) and be done with it, but I'd like to
simply say that everything's braced against lateral forces, and be done with it.

What have any of you other bridge guys done in this case?

{Bear in mind there are no seismic forces to deal with; only wind and vehicle
braking).

******* ****** ******* ******** ******* ******* ******* *** 
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) to the list, send email to 
*   admin(--nospam--at)seaint.org and in the body of the message type 
*   "join seaint" (no quotes). To Unsubscribe, send email 
*   to admin(--nospam--at)seaint.org and in the body of the message 
*   type "leave seaint" (no quotes). For questions, send 
*   email to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********