Overstrength Factor Applicable?

[msquared48]

Does the ASCE seismic overstrength factor apply to the tension uplift design for column baseplates?

Mike McCann, PE, SE (WA)

 

[KootK]

What kind of frame Mike? SCBF?

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.

 

[msquared48]

Yes.

Mike McCann, PE, SE (WA)

 

[KootK]

I believe a nearly identical question is currently being answered here: Link

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.

 

[sandman21]

That thread is for an OCBF. ASIC 341-10 F2.3 specifies the requirements. This will change in 341-16 and the overstrength option will be removed and capacity based designed will be used.

 

[KootK]

For me, rationally, the answer in both threads is the same: design the anchorage uplift for..

1) the vertical uplift component of the maximum force demand that governed the brace design at that level plus;

2) the vertical uplift that governed the column tension design.

Anything less strikes me as an inconsistent load path.

I don't remember where it exists -- or even if it still exists -- but I recall a provision for multi-story buildings whereby one did not have to consider the improbable case of every brace at every level going plastic at once. To the extent that may still be the case, I would expect that same logic to apply to the component of anchorage uplift coming in through the column. That could come in handy in a challenged connection design I would think.



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.

 

[sandman21]

I only mention since they have two different requirements and the requirements diverge. It would appear that the code has chosen your path for uplift forces. I unaware if the code ever had a provision allowing a partial look at the brace configuration, AISC 341-10/16 F2.3 requires a look at the bracing for the different failure modes, compression/yielding. OCBF does not have these requirements.

 

[Deker]

KootK - Perhaps exception 2c for non-linear analysis in section F2.3 is what you are referring to?

 

[KootK]

I only mention since they have two different requirements and the requirements diverge.

And it's a good thing that you did. I have a tendency to speak in terms of general principles and fail to give folks the specifics that they need to move forward.

KootK - Perhaps exception 2c for non-linear analysis in section F2.3 is what you are referring to?

I honestly don't remember where I picked that up but, yes, I suspect that provision is the current path towards taking advantage of the stochastic unlikeliness of full height yielding. The clip below is from the 2016 steel seismic code commentary. It's not what I was referencing but discusses the concept and makes it clear what the expectations are now.

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.