huangyhg

stiffness of base plate on perimeter wall
i am trying to figure out the stiffness of a base plate for a steel column resting on a perimeter foundations wall. i am running through the procedure in the pci design hand book (section 3.8.2). using the pci i can easily calculate the flexibility of the base plate and the anchor bolts but i’m not sure how to account for the flexibility of the foundation wall/footing.
the pci does give an equation for the flexibility of the foundation but that is for an isolated footing only.

flexibility is the inverse of stiffness, ei is the stiffness. the foundation wall will have much greater stiffness, (order of magnitude greater).
i understand that flexibility is the inverse of stiffness. in the pci they have an equation for the flexibility of the footing = 1/(soil modulus * moment of inertia of footing)esentially 1/ei. this is for an isolated footing. for a column that is going to be on a foundation wall would you assume then that the foundation is infinitely rigid because the moment of inertia for the wall footing would be incredibly large?
if you are talking about a long stemwall, 8" to 10" thick, four to 8 feet high...most definitely assume infinitely rigid.
however, if you are talking about a short 6" thick stemwall, one foot or less high, over a thin strip footing, i would look to the spread footing comparison.
anything in between, assume something between a spread footing and infinity. that close enough for you?
mike mccann
mmc engineering

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