Timber Cribbing seismic

[EIThelp]

Doea anyone have experience analyzing timber cribbing for seismic forces? The cribs components are all connected with bolts and angles, and rigidly connected to the superstructure. However, the existing cribs themselves are just sitting on grade. I am concerned that as there is no positive connection to the ground the superstructure and cribs will slide should there be a seismic event, however, these buildings have seen several mild earthquakes and are still standing - I am not sure how that is. Any help would be appreciated.

 

[EngineeringEric]

What would happen if the earth shifted under the cribbing? would the cribbing fail or just slide? Maybe this is this like base isolation and a flexible post at that?

I have never seen or used cribbing for anything besides temporary construction and therefore seismic was never a consideration.

 

[EIThelp]

I think the whole building would slide. Base isolation has a maximum amount of movement - limited by the isolators. There is nothing stopping these buildings from significant sliding. Is there anything specific in the code that requires building be anchored somehow to the earth beneath?

 

[MotorCity]

What is the purpose of the cribbing? Is it simply temporary shoring that was abandoned in place or does it serve as the foundation? Typically foundation elements do not consist of timber members just sitting on grade. Are there any sort of concrete walls, footings, piles, etc? Can you post a photo or sketch?

 

[EngineeringEric]

The comment on isolators wasn't calling it an intended isolator but rather that is analogous to how it is transferring load. I agree the building would slide around, but if it slides than there is far less lateral load exerted on the system (a benefit for poor construction!)

This isn't really a code thing... it isn't a foundation and sounds unsafe. Timber cribbing is a temporary support for during construction. Even if this thing was placed 4ft under fill on top of a concrete foundation it still wouldn't work. You can add all the diagonal braces in the world to this, and have those anchored to piles, and it still should not be done for 99.9% of structures