Foundation Rocking - How to determine if it will occur
Foundation Rocking - How to determine if it will occur
(OP)
In seismic zones, how do you determine if a concrete shearwall or a steel braced frame will rock or not? Does anybody have a reference for how to determine this effect?






RE: Foundation Rocking - How to determine if it will occur
Do you mean deflect? Yes - they always will deflect to some degree.
Are you concerned with overturning?
RE: Foundation Rocking - How to determine if it will occur
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Foundation Rocking - How to determine if it will occur
This can be used as a form of energy dissapation in seismic analysis, however the redistribution of forces is beyond linear analysis. I am only familiar with the concept, not the detailed analysis.
RE: Foundation Rocking - How to determine if it will occur
I am in the same boat as keenaseng where I am marginally familiar with the concept but not familiar at the detailed analysis. Its possible that rocking of the foundations can cause redistribution of the forces, as well as increasing the building period and increasing the amount of drift a building undergoes.
That said, I would appreciate it if anybody has any design references they can point me to on this.
Thanks for any help you can provide.
RE: Foundation Rocking - How to determine if it will occur
Are you purposely trying to let the foundation rock? Or are you trying to design a foundation system and are worried if the foundation rocks what will happen to the structure?
RE: Foundation Rocking - How to determine if it will occur
RE: Foundation Rocking - How to determine if it will occur
RE: Foundation Rocking - How to determine if it will occur
RE: Foundation Rocking - How to determine if it will occur
I just have a plan review comment that my seismic joint may not be big enough because of rocking, and I need to check the rocking aspect.
RE: Foundation Rocking - How to determine if it will occur
It is an engineering term as well, and is used in the 2010 California Building Code to amend ASCE 7-05, chapter 17.
However, it will not be used in plain vanilla or cookbookish building code analysis.
RE: Foundation Rocking - How to determine if it will occur
Or is there anything else that will save you from having rocking occur (besides upsizing your footings). For instance, if you have a wood diaphragm, it would seem somewhat difficult for a braced frame with large footings to rock when the load is being transmitted to it by a bunch of nails in 1/2" plywood. If the diaphragm yields, is that one thing that might prevent rocking from occuring?
RE: Foundation Rocking - How to determine if it will occur
RE: Foundation Rocking - How to determine if it will occur
"The use of these provisions will decrease the design values of the base shear, lateral forces, and overturning moments, but may increase the computed values of the lateral displacements and the secondary forces associated with the P-delta effects"
RE: Foundation Rocking - How to determine if it will occur
Judging from what ATSE and you have said, this is rocking of the actual foundation, ie, a slight overturning or rotational movement of a foundation? I would think this would be more of a phenomenon in very stiff shear walls with relatively short foundations, like stairwells and similar structures. But I will stay tuned to see where this discussion goes.
This rocking action would be in addition to story drift of your braced frame or shear wall...
RE: Foundation Rocking - How to determine if it will occur
Mike McCann
MMC Engineering
RE: Foundation Rocking - How to determine if it will occur