R-Value for moment frames

[peinapod]

I'm not seismically detailing my moment frames. Therefore, my steel is designed for R=3. Does anyone see any reason why I can't design my foundation with a higher R? Maybe 6 or even 8? Changing the welding characteristics around the beam to column connection will not change the loads on to the footings. I can't see why IBC would prohibit this.

 

[ishvaaag]

One must stay consistent in the whole structure. Except that to stay consistent is mandated by the code to use different R factors, use the same value.

Models are just like theories to reality, ways of understanding the thing.

The loads may be the same but the code may be thinking in that some details require for the targeted reliability different hypotheses to start with. So in the same manner that different methods of ensuring safety for different structural materials are required, also different methods to analyze different components are.

This may or not apply to the question you are asking, yet if there is definite option in the code I would document myself before going against it on my engineering judgement.

This of course is not the case for things one is entirely sure has the whole picture about. But to have the whole picture of things like the implied reliability of the coders is something that escapes more practicing designers, if only -but not only, heh- by their changing nature and lack of time to analyze their always being renewed content.

 

[haynewp]

There was another post in the 'structural other topics' forum that was suggesting the opposite, (using a lower R for foundation design). I think you should use the same R unless the code says otherwise.
I see what you are saying that how does the foundation know that the frames are not seismically detailed. But there are a lot of things like this in the building codes that really don't make complete sense but we have to do them anyway.