Min Pressure on Elastomeric Bridge Bearings

[jpnj]

There is a minimum pressure requirement (for steel superstructures) of 200 psi (1.38 MPa) from dead load and superimposed dead load on elastomeric bearings to ensure proper operation of the bearing. In AREMA 2000 Chapter 8, section 18.3.10, it says if you do not meet this 200 psi minimum requirement, the bearing 'shall be restrained against horizontal movement'. I do not understand how an expansion end bearing would work if I have to restrain against horizontal movement?

I would appreciate any thoughts or help anyone could offer, or even the name of a good bearing manufacturer that I could discuss this with.

Specifics:
55 ft (16.7 m) span steel plate girder bridge to carry rail traffic, located in Paducah Kentucky
Dead Load = 37 kips (165 kN)
Live Load = 185.3 kips (824 kN)
Impact = 100.7 kips (448 kN)
Total Design Reaction = 323 kips (1437 kN)
Bearing size 24" (610mm) x 16" (406mm)x 2" (51mm)
with 3-11 gage steel reinforcing shims

 

[Qshake]

First let me say that I'm not familiar with that specific requirement in AREMA. But yet I've been around awhile and feel qualified to drop my $0.02.

In my interpretation, the bearing needs to be restrained against "walking" or "wobbling" off from directly underneath the girder. This can be accomplished by using "keeper" plates which are nominal steel plates that are bolted to the beam and surround the bearing. Of course, the bearing in these cases is the elastomeric type.

The restraint is not meant to inhibit the necessary thermal movement which is taken up by the shear deformation of the elastomer.



Regards,
Qshake

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[yli]

Minimum pressure or uplift is the major concern of bearing design, this applies to both neoprene bearings and pot bearings. In the case of skewed bridges or curved bridges, a lot of efforts needed to deal with this issue.

In response to your question, My limited experience is this: neoprene can be hot bonded to sole plate, and restraint bar (0.5" x 0.5" x length) can be welded to masonry plate with 0.125" gap between bearing pad and restraint bars. If hot bond is not preferred, same restraint bar can be welded to sole plate too.

 

[VoyageofDiscovery]

Hi jpnj,

I use internal pintles or external keepers at the corners.

VOD

 

[jpnj]

Thank you all for your helpful responses, I received replies to inquiries to the NYS DOT and a representative of AASHTO that also said the requirement is to prevent walking of the bearing. They both said some states are 'backing off' this requirement if the elastomer is vulcanized to the plate, or they suggest the use of restrainer guide bars.

Thanks again!
jpnj