Repairing an elastomeric bearing
Repairing an elastomeric bearing
(OP)
I got sucked into another headache. Three elastomeric bearings that are partially delaminated from the masonry plate. The bearings in question are at an abutment. Photos and a framing plan are attached.
Bridge particulars: 3 span continuous stringer, W33x291; 10 stringers. Span lengths are 100’-110’-100’; deck with is 55’; 30-degree skew; expansion bearings at the abutment; fixed bearings at the piers.
The bearing at Girder 1 appears to have rotated ½” east; two bearings in the middle have rotated about ¼” east. No other bearings on this bridge or the adjacent bridge have delaminated. (The adjacent bridge is the one with the railing base plate spanning an expansion joint "Stupid Construction Questions").
The neoprene is vulcanized to the masonry plate. Is there any way to repair this? I waiting for a call back from the manufacturer but I’m interested in the experience of others. The owner is more interested in a repair rather than a cause.
There’s another thing that may or may not be related to the delamination problem: These bearings have been a headache since they were installed about 18 months ago. Every expansion bearing – on both bridges - leans more than what would be normally expected in the expansion direction at relatively mild temperatures – 70 degrees. They were reset once but the lean returned. Unfortunately I can’t get any information about the conditions under which the bearings were installed or reset; also no one in the office knows where the calculations are.
Last year when the leaning issue came up I was too concerned because the “excessive” lean was tolerable (elastomeric bearing tend to be forgiving). I did a check and the bearings have enough thickness.
Right now, I’m wondering if the problem is due to a manufacturing defect, an installation defect, a rotation of the superstructure, or a combination of these. I’ve seen skewed bridges that have rotated about the longer diagonal. However, the opposite span is fine and there’s no problem with the adjacent bridge. One other thing, at Bearing G1, there was a partial blow out in the end of the parapet formwork. A portion of the expansion joint was jammed. I'm wondering if somehow the bridge locked up resulting in damage the bearing. The end of the parapet is spalled.
Bridge particulars: 3 span continuous stringer, W33x291; 10 stringers. Span lengths are 100’-110’-100’; deck with is 55’; 30-degree skew; expansion bearings at the abutment; fixed bearings at the piers.
The bearing at Girder 1 appears to have rotated ½” east; two bearings in the middle have rotated about ¼” east. No other bearings on this bridge or the adjacent bridge have delaminated. (The adjacent bridge is the one with the railing base plate spanning an expansion joint "Stupid Construction Questions").
The neoprene is vulcanized to the masonry plate. Is there any way to repair this? I waiting for a call back from the manufacturer but I’m interested in the experience of others. The owner is more interested in a repair rather than a cause.
There’s another thing that may or may not be related to the delamination problem: These bearings have been a headache since they were installed about 18 months ago. Every expansion bearing – on both bridges - leans more than what would be normally expected in the expansion direction at relatively mild temperatures – 70 degrees. They were reset once but the lean returned. Unfortunately I can’t get any information about the conditions under which the bearings were installed or reset; also no one in the office knows where the calculations are.
Last year when the leaning issue came up I was too concerned because the “excessive” lean was tolerable (elastomeric bearing tend to be forgiving). I did a check and the bearings have enough thickness.
Right now, I’m wondering if the problem is due to a manufacturing defect, an installation defect, a rotation of the superstructure, or a combination of these. I’ve seen skewed bridges that have rotated about the longer diagonal. However, the opposite span is fine and there’s no problem with the adjacent bridge. One other thing, at Bearing G1, there was a partial blow out in the end of the parapet formwork. A portion of the expansion joint was jammed. I'm wondering if somehow the bridge locked up resulting in damage the bearing. The end of the parapet is spalled.





RE: Repairing an elastomeric bearing
As far as I know there isn't a repair other than replacement but I'd be interested in hearing more.
RE: Repairing an elastomeric bearing
Would it be possible to provide a beveled plate under the beam flange to account for the slope?
RE: Repairing an elastomeric bearing
Just a thought, but if the diaphragms were detailed for steel weight fit, this could be caused by a twist in the exterior girder. With the diaphragms square to the girders you will see a twist in G1 between when the diaphragms are installed and when the total dead load is applied, both due to the differential deflection between the girders and the girders rotating perpendicular to the abutment diaphragm rather than the centreline of bearing. Are the abutment bearings installed perpendicular to the abutment diaphragm or parallel to the girders (it looks like the former from the drawing).
RE: Repairing an elastomeric bearing
I have seen a curved skewed bridge "walk" on it's bearings before, but they were steel roller bearings. I think the superelevation along the curve was probably the cause of that though.
I agree with BridgeEI that the skew has something to do with the pad deflection you are seeing. The skewed rolled beam bridges I have designed have all been simple spans, not continuous, but I have always staggered my diaphragms which makes the superstructure a bit more flexible. I wonder if the contiguous spacing is exaggerating the girder twist that gwynn is mentioning?
I wonder if the deflection is really that big of deal. AASHTO limits pad deflection to half the elastomer thickness. I would guess there's more than 1" of elastomer in those pads. Just a thought. However, I am not familiar with vulcanizing pads to masonry plates. We don't do that in Oklahoma.
On a side note, was there a superstructure depth constraint on this bridge? 4'-4" to 5'8" beam spacing is quite small. I understand that the beam spacing and continuous spans allows for a smaller depth beam to be used. That framing plan looks expensive to build.
RE: Repairing an elastomeric bearing
DIAPHRAGMS FOR SKEWED STRAIGHT GIRDER SUPERSTRUCTURES SHALL BE FABRICATED TO FIT GIRDERS ERECTED WITH THEIR WEBS LAID OVER (OUT OFPLUMB) UNDER THE STEEL DEAD LOAD CONDITION. GIRDER WEBS SHALL BEVERTICAL AFTER APPLICATION OF FULL DEAD LOAD.
The manufacturer is looking into things as well. I asked the resident engineer to check if the stringers are plumb and to measure the elastomer height at all four corners of the north abutment bearings. If all of the acute corners had problems I could write it off to rotation, but as Lt. Colombo would say, "there's still something bothering me".
OSU - I don't know why the stringer spacing was tight; clearance isn't a problem. I was never involved in the design; I only got involved because of the problems that surfaced during construction; pretty much from day one.
My next headache is to look into the deck cracking.
RE: Repairing an elastomeric bearing
RE: Repairing an elastomeric bearing
RE: Repairing an elastomeric bearing
I don't think the masonry plate is necessary - I would be inclined to leave it alone and seal the edges - but the delamination has reduced the bearing area; it'll probably fail in time if nothing is done.