Aligning lead-rubber seismic isolators

[BridgeSmith]

We've had the issue come up a few times now where our seismic isolators are mis-aligned because the steel girders weren't at the base-line temperature when the girders were set and attached to the isolators. So, then they're deformed when they're not supposed to be, and have the potential to be laterally deformed more than allowed at the extremes of the temperature range.

I'm curious if anyone has seen a solution/mitigation strategy for this issue?

 

[jhnblgr]

Are the bolt holes slotted in the masonry plate so you could adjust that way?

 

[BridgeSmith]

In order for it to function properly for energy dissipation/damping, nothing can be slotted. The only movement that's allowed is deformation of the steel-reinforced elastomeric bearing and lead core.

 

[jhnblgr]

Then the only alternative is
1. Use a jack to deflect the top of the bearing to the correct location on the beam and weld at the attachment location at the time of installation. Similar to how a log splitter works.

 

[BridgeSmith]

Then the only alternative is
1. Use a jack to deflect the top of the bearing to the correct location on the beam and weld at the attachment location at the time of installation. Similar to how a log splitter works.

You'd need a big jack, at least 20 tons(probably 50 to 100 tons on larger bridges), to deflect those isolators, but the real issue with that is there's usually not anything to jack against, except maybe at the abutment if it needed to be moved away from the backwall. There typically wouldn't anything solid to push off of at a pier.

 

[jhnblgr]

Once proper temperature is reached Cut the weld holding the girder, Jack the girder up and allow for the elastomers to relax to normal and lower the girder and weld to new location.

Could you design for a larger temperature differential. Would make your bearings larger and taller.

 

[BridgeSmith]

Once proper temperature is reached Cut the weld holding the girder, Jack the girder up and allow for the elastomers to relax to normal and lower the girder and weld to new location.

They might be able to do something like that, although I suspect they'd want to do something other than welding as a temporary connection. Using bolts in a slot as a temporary connection, and then loosening, jacking, resetting and then welding might be an option.

Could you design for a larger temperature differential. Would make your bearings larger and taller.

That's an option to consider, also. It might only make then a little larger diameter. The height is typically controlled by the maximum allowed stiffness (i.e. controlling the max force transferred to the substructure).

Thanks you for the ideas.

 

[bugbus]

I was watching a TV show about the construction of the Gateway Arch in St Louis MO. I can't remember if they used cold water or warm water, but they doused one side of the arch to the two halves to align at the top so they could install the final piece.

I've never seen it done with bridges, but it doesn't seem that crazy. Maybe there's a more practical solution than water, e.g., heated blankets or similar.

 

[BridgeSmith]

Maybe there's a more practical solution than water, e.g., heated blankets or similar.

Could be, but any solution has to be implemented by the 'lowest bidder', so we always have to keep that in mind.

 

[Angelina12]

Consider employing composite girders with thermal characteristics that are more adapted to extreme temperature changes.

 

[BridgeSmith]

Consider employing composite girders with thermal characteristics that are more adapted to extreme temperature changes.

Steel girders work well in extreme temperatures, and they are composite with the concrete deck.