Shear Keys for railroad bridge wingwalls

[brandonl]

I recently heard it said that a footing shear keys (to resist sliding) in wingwall footings are not acceptable for a railroad bridge. The local railroad authority's standard criteria mentions nothing of the sort. I don't have a copy of AREMA manual.

Does anyony know if this is an AREMA requirement? Is this statement a generally accepted practice in railroad bridge design? I could possibly see the argument in favor of this statement for the actual bridge abutments due to the need for some movement in order to mobilize the passive pressure on the key. But in my opinion, a shear key would be acceptable for the wingwalls.

I would appreciate your thoughts and opinions. Thanks.

 

[purdue86]

The first thing that you should do is obtain a copy of chapter 8 of the AREMA manual. Do you design highway bridges without AASHTO?

The second thing that you need to realize is that the AREMA manual is manual of recommended engineering practices - not a set of specifications. If the railroad tells you to use them as specifications, then they are specifications. But if the railroad tells you to do something different, then you follow whatever the railroad says unless it violates your professional integrity.

I took a quick look and could not find any prohibition on shear keys in chapter 8. If I remember soil mechanics correctly, movement is required to create passive pressure - no matter where it is (toe or shear key).

As a railroader who checks bridge plans, I would likely allow a shear key if I believed that it could be properly constructed. I would be more inclined to allow it for a completely new structure than for a replacement structure. Bridge replacement under traffic is difficult enough without building a shear key. I would likely tell you to increase the thickness of the slab and develop the passive pressure on the toe.

 

[brandonl]

Thank you purdue86. Thanks for taking a quick look in the manual, I really appreciate that. The question is in reference to a RR bridge that is already designed, with a shear key on a portion of the wingwall footings only. The abutments are supported completely on piling.

In this case, the soils are a stiff clay, which I understand to be very suitable for constructing footing keys.