Moment Frame Base Plate Calculation
Moment Frame Base Plate Calculation
(OP)
Hello folks,
I modeled an ordinary steel moment frame with pinned bases and now I'm coming to you all with a question that has been gnawing at me for some time.
Should I design the moment frame base plate as the more conservative 'fixed' condition or can I stick with the 'pinned' base condition?
In addition, does anyone have any suggestions/theory/raw calculation procedures to help design a moment frame/base plate on a concrete column where concrete breakout (tension) is the governing restraint. I was hoping to weld the base plate to rebar and further confine the entire member with stirrups, instead of anchor bolts. Does anyone have any suggestions?
Do I need to be conscious of electrolysis or another corrosive aspect between the rebar and the baseplate?
Thank you all,
R
I modeled an ordinary steel moment frame with pinned bases and now I'm coming to you all with a question that has been gnawing at me for some time.
Should I design the moment frame base plate as the more conservative 'fixed' condition or can I stick with the 'pinned' base condition?
In addition, does anyone have any suggestions/theory/raw calculation procedures to help design a moment frame/base plate on a concrete column where concrete breakout (tension) is the governing restraint. I was hoping to weld the base plate to rebar and further confine the entire member with stirrups, instead of anchor bolts. Does anyone have any suggestions?
Do I need to be conscious of electrolysis or another corrosive aspect between the rebar and the baseplate?
Thank you all,
R






RE: Moment Frame Base Plate Calculation
Nope. You ought to be fine.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Frame Base Plate Calculation
Do you have any suggestions on how I should design the base plate? Pinned values or go with the more conservative fixed values?
RE: Moment Frame Base Plate Calculation
DaveAtkins
RE: Moment Frame Base Plate Calculation
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Frame Base Plate Calculation
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RE: Moment Frame Base Plate Calculation
@Dave - Thank you for your input.
@Teix - Okay. You would assume that the assembly has an inherent 10% rotational stiffness?
RE: Moment Frame Base Plate Calculation
Guaratee is a pretty strong word. The only way to guarantee pin like behaviour is to build a pin. And that's pretty impractical for most column base situations. Bridge folks do it more often.
One strategy is to ensure that the connection could absorb moments safely until a part of the connection yields and the connection effectively turns into a pin. This usually means designing all brittle failure modes like concrete breakout and crushing so that they will occur safely after at least one reliably ductile failure mode like anchor bolt or base plate yielding.
So small, well developed anchor bolts and thin, expansive base plates will promote base connection flexibility. Trouble is, you often need these same elements to resist significant axial tension as well which works against you. Some engineers will place the anchor bolt inside the column flanges under the premise that a smaller lever arm to the bolts means more pin like behaviour. I disagree and think that a smaller lever arm usually just means that you'll just initiate a brittle anchor breakout failure or concrete crushing failure sooner in the load history.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Frame Base Plate Calculation
Mike McCann, PE, SE (WA)
RE: Moment Frame Base Plate Calculation
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Moment Frame Base Plate Calculation