Direct Analysis Method - Notional load to account for plumbness error

[SuG89]

Hello,

I am modelling a new facade which is supported by the exterior columns of an existing building. These columns are fully pinned at the top and bottom in the FE-model and hence no translation is allowed.
I want to include the notional loads (0.002 x Yi) on the columns but not sure about two things-
(1) Are notional loads applicable to this situation?
(2) As mentioned above the top support is fully pinned. How can add the notional load when there is a support at the top?

Regards.
Su

 

[JoshPlumSE]

Instead of using notional loads, why not model the column as out-of-plumb. Seems an easier way of doing this for such a small / simple model.

 

[MotorCity]

Notional loads would be applied in the same manner as other gravity loads on the column regardless of column fixity.

 

[JoshPlumSE]

If the FE model has a lateral restraint boundary condition at the top of the column, then the notional load will go directly into the boundary condition and will not cause any moment or shear in the column.... defeating the main purpose of the notional load.

 

[WillisV]

If the top and bottom are both pinned then K=1 and you don’t have to worry about all that mess.

 

[SuG89]

Thanks everyone for the responses!

@JoshPlum - Out-of-plumb is an option but that involves some re-work. Therefore I wanted to find out about other possibilities. A colleague of mine suggested to use equivalent member line load on the column instead of applying notional point load at the top of column (which, as pointed out by you, goes directly into the supports). I am considering using this approach.

 

[KootK]

Are notional loads applicable to this situation?

I think that this question is the crux of this and I would say that the answer is probably no. I believe that the notional load business is about the stability of the whole building or at least substantial sub-assemblies within it. The weight of your cladding system should add to the magnitude of the notional loads applied to the lateral system, likely as loads applied to your diaphragms. If these columns are part of the building lateral system, then they will be affected in this way via the addition lateral loads brought on by the additional notional loads. If these columns are not a part of the building lateral system, then I don't think that the notional load business comes into play. It's worth noting that non-lateral column design procedures assume a similar degree of misalignment within the column span. As such, to also include notional loads in the design of gravity only columns is really to account for that effect twice, redundantly.

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.