What is the maximum length one might consider using beyond the center line of bearing on a plate girder bridge? I am concerned about the uplift at the end.
Maximum span length? or Maximum length from the very end of the girder to the centerline bearing?
If it's the latter, this distance is typically controlled by the equivalent column section formed by the web and stiffeners. AASHTO has precribed amount that may be considered for the effective column web distance.
Obviously such distance would be no more than absolutely necessary.
Regards,
Qshake
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Sorry Bridgemann, uplift? I find your post confusing. Could you please clarify?
To add to what Qshake said, there might be a minimum distance beyond support stiffener by code if working on seismic region. It is supposed to prevent unseating of the span in the case of earthquake.
Also it will depend on what kind of bearing you have.
Continuous span bridges with a short span next to a much longer span usually result in an upward reaction. One way to get around this is try to make your spans closer to the same length or you can always provide a stopper so that the girder can't move upwards at the bearing. I've seen numerous situations like this for rehab jobs.
Are you asking about the maximum length the end of the girder should extend beyond the centerline of bearings? I don't know that there is a maximum allowable. I think you would need to determine what length you need and see if it's doable. Will there be too much vertical offset at your joint? Will the negative moment over the support be too great?
Sorry for the confusion. This is a bridge rehab project and the cl of bearing of the girders at the abutment is not parallel to the the backwall. The girders extend to 3 1/2" of the backwall to support the deck slab. The distance from the centerline of the bearing on each girder to the end of the girder varies from 6" to as much as 2'. I am concerned about the uplift that would occur with that 2' cantilever. The bridge is on a curve and on a skew. The maximum extenstion beyond the cl of bearing is in the obtuse corner side of the bridge.
Why don't you do a deflection check? It should be relatively simple and it will tell you if you really have a problem or not. Chances are that the deflection up will not be more than a couple of mm.
Two feet from *centerline* of bearing to the very tip of the girder seems pretty normal to me. You're just talking a few hundred pounds of steel; I don't think the bridge would notice.
If you have a problem with upward deflection at the end of the girder (24"x slope at support) you will have a much bigger problem with center span deflection. Two feet is not unusual.
Michael.
Timing has a lot to do with the outcome of a rain dance.
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