Elastomeric Bearing Splitting 2

[dbags]

I have a condition on a new bridge in service for approximately 2 years. The bridge is a 5 span continuous plate girder bridge on a horizontal curve (r=650'). The round steel reinforced elastomeric bearings at the abutments have formed vertical cracks (typically 3 per bearing at about 120 degrees from each other). Otherwise, the bearing appears to be functioning well with the typical shear translation and compressive bulging in between laminae. Why would this type of cracking occur in this application???

 

[TTK]

Could you provide us with more information, such as the diameter of the pads, height of pad, and Design Method used (A or B)?

Also, the span arrangement of the bridge might help.

Thanks

 

[VoyageofDiscovery]

Hi dbags,

This situation you describe is mystifying. Horizontal cracks maybe, vertical I've never seen that.

Have a look at the shop drawings for these bearings, was there extreme cover around the internal shims? If so I was thinking hoop stresses, but 3 cracks, I don't know.

Regards

VOD

 

[dbags]

I found the source of the problem through email converstation with Roeder & Stanton of University of Washington. They believe it is likely "the vertical slot that occurs in the rubber cover is caused by a vertical keeper bar that holds the horizontal plates in place during fabrication. Fabricators usually patch the slot after molding the bearing by cold-filling it with mastic (which sometimes cracks over time at the edge of the slot - I suspect that is what has happened here) or in some cases they (hot-) vulcanize a piece of rubber there. The latter is the better way to go, but is a more complicated and therefore expensive operation.

The circumferential stresses in a circular bearing are pretty small, so the bearing is very unlikely to start tearing itself apart as a result of the vertical crack. The main danger is that moisture might get in and start corroding the steel plates. If that is perceived as a problem, then someone could go out and re-glue the mastic filler pieces in place."

 

[TTK]

dbags,

Thanks for sharing the knowledge on the source of the problem....you get one star from me!