Seismic Elastomeric Bearings - Testing Problems

[abjr]

We have some Steel Laminated Elastomeric Bearings to be used on a bridge for both thermal movement and seismic isolation. The testing requirements for the bearings states that each bearing shall be shear tested for a displacement of 5.25 inches. The laminated bearings are only 4.025 inches total thickness. Per AASHTO Method A & B the total height of the bearing is to be greater than or equal to 2 times the shear displacement. Does anyone know if a laminated bearing of only 4.025 inches will be able to shear 5.25 inches without failure? Does anyone have any similar experience with steel laminated elastomeric bearings? By exceeding the AASHTO requirements, is the bearing destined to fail?

Thank you for any help.

 

[corrosionman]

I'm fairly new to bridge bearings but I've been in the rubber field for 35 years and there is no way your bearing will move 5 inchees without total failure. At this moment I'm checking a 164 feet span road bridge and the total thermal movement is only 18 mm from winter to summer so you have a strange request. Best of luck CM

 

[TTK]

I suspect that you are testing non-production pads (i.e. random sample from lot that will not be used in the final structure), so testing to failure may be desired.

With that said, the shear displacement value does seem odd for the bearing height.

 

[SoeSoe]

Is the 5.25" for your MCE? I agree with the Mecha above, no way. Seismic isolation refers to energy dissipation, I think? Sounds like you need a bridge engineer, not an internet forum.

 

[abjr]

No, we are testing each and every production pad - not just a few test pads to failure. Every pad tested is to be installed in the bridge. As I understand it, the Design Engineer on the project expects a 5.25 inch displacement in case of a seismic event. Doesn't the displacement seem large for a little over 4 inch pad?

 

[Qshake]

It seems incredibly large for a bearing of that height. You may typically expect a lead-rubber isolation bearing to move 5" with a height greater than 10". Even in those cases I always tell my engineers that they must also remember to allow for the 10" movement....which in retrofits of old structures is often forgotten about until that diasterous moment when the backwall or step-wall interupts the movement!!

Regards,
Qshake

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