Hydrostatic tension in elastomeric bearings
Hydrostatic tension in elastomeric bearings
(OP)
The code and the commentary in AASHTO LFRD Sec. 14.7.5.3.3 seem to be contradicting each other. The code says "In bearings with externally bonded steel plates on both top and bottom, the peak hydrostatic stress shall satisfy:".
The commentary says "However, in a bearing equipped with external plates, upward movement of part of the plate can cause internal rupture due to hydrostatic tension. Provisions have been added to address this case."
I am designing bearing pads using Method B, and we never specify the pad to be bonded to the anchor (or sole) plate. The way I read the code, I only have to worry about hydrostatic stresses if my anchor plate is bonded to the pad. The way I read the commentary I should check hydrostatic stresses because I have an external plate.
Did they just forget to put "bonded" between external and plates or am I missing something here?
The commentary says "However, in a bearing equipped with external plates, upward movement of part of the plate can cause internal rupture due to hydrostatic tension. Provisions have been added to address this case."
I am designing bearing pads using Method B, and we never specify the pad to be bonded to the anchor (or sole) plate. The way I read the code, I only have to worry about hydrostatic stresses if my anchor plate is bonded to the pad. The way I read the commentary I should check hydrostatic stresses because I have an external plate.
Did they just forget to put "bonded" between external and plates or am I missing something here?





RE: Hydrostatic tension in elastomeric bearings
I have my calculations to automatically check the hydrostatic stress but I have a note off to the side saying it's only required for bonded bearings. Most of the time the calcs check out and I don't need to have the bearing bonded, it's rare when I have called for it.
RE: Hydrostatic tension in elastomeric bearings
The question remains though, why bond pads to an external plate in the first place?
RE: Hydrostatic tension in elastomeric bearings
I used expansion a lot so hopefully I didn't make it confusing...
RE: Hydrostatic tension in elastomeric bearings
RE: Hydrostatic tension in elastomeric bearings
I think a better reason to bond the pad to the anchor plate would be if the bridge had a tendency to "walk" off the bearings. I've seen this on a curved bridge before where one end of the bridge was moving off the bearings. That particular bridge had steel rocker bearings though.
I've also heard of people bonding the pad to the anchor plate when the span configuration causes uplift. I'm not sure that's how I would address uplift.