Is it possible to do a partial fixed base plate? How?

[X4vier]

Is it possible to do a partial fixed base plate? How?
Considering the foundation is capable, is there any way to do a partial fixed base plate for a steel column?
I guess if partial something in the connection will yield. Is that safe?

 

[human909]

It’s all good! Pushback is healthy

Agreed! It is the way I learn and explore knowledge. Though in this thread I think there has been more furious agreement than strongly different opinions or outlooks.

That is what I find fantastic about the discussion on this forum is there are very intelligent and experienced professionals here and there is plenty to learn simply by allowing your outlook to be challenged or challenging others out look.

Only occasionally do I actually start a thread and ask specific questions... But I quite thankful today for the Engtips responses to my last thread where I asked about fatigue resources. I spent a half the day on site today inspecting a structure with fatigue issues and in a harsh environment, I'm a long way from an expert but it didn't take a rocket scientist to spot the issues, and likely future issues.

 

[canwesteng]

One thing re: bones comment about h/400 wind deflections - ASCE 7 wind is not meant to be use for serviceability cases. Even applying the 0.6 factor to get to ASD wind loads is overestimating the wind for SLS imo. Personally, I go with wind speed for low importance buildings and the 0.6 ASD factor for SLS wind loading, which is in with the NBC approach, and more like a 0.5 reduction.

Sorry for side tracking everything

 

[lexpatrie]

But I don't believe that if you do choose to deviate from it then it necessarily is poor practice

Granted, there's a scenario where conventional analysis will be "wrong" but it may still be safe (incorect and conservstive).

The dangerous stuff is the "I've decided this is what's happening" i.e. the inflection point functioning as a brace without providing a stiffener or explicit brace, (or research justifying it). I am aware of no research that established that as factually accurate, I believe it was basically a meme or folklore in the structural community passed from mentor to mentee.

If you read a lot of the articles on connection design they get into lower bound and upper bound theorems, which is where all of this is intended to live. The basic analysis approach is intended to address equilibrium and statics on a stable, erected, appropriately braced structure.

If you satisfy statics and equilibrium you have a valid potential design, it may be over designed, as I recall. Speaking off the cuff based on potentially incorrect recollection.....

This is going to be poorly worded....


Portal frame (and the cantilever one whose name eludes me) presumes a location of zero force, this is generally unconservative, but is decent for prelimiary design (and in the 1940s when there wasn't much alternative that was more grounded in reality). Because it presumes a force distribution despite statics being satisfied, it can be unconservative. It is essentially an energy method without being obviously an energy method (energy method presumes a force distribution or deflected shape and arrives at a "solution" based on that. These approaches can find a "solution" that is an upper bound (the structure slash forces cannot be higher than the arrived solution, but there may be a lower solution, so when it's a buckling or stability issue, it can overestimate the critical load.... i.e. unconservative.

This is perhaps beyond the scope of the discussion here...

 

[bones206]

@canwesteng - Agreed, i also use a reduced wind speed for drift checks. Usually via 0.7*0.6W = 0.42W, per ASCE 7-10 commentary. Not sure what the OP's building code is, but we may have scared them off at this point

 

[lexpatrie]

If anyone is interested more back to the main thrust of this thread,

Influence of partial base fixity on frame stability, Galamobos, ASCE J. Struct. Div., 86, ST5. (May 1960), 85-108.

You can probably look for more recent articles as they should refer to this one.....