force & shear in seismic 1

[hocho]

can any confirm that the only reason we compute or determine story forces in seismic is to calculate for base shear or story shear and the forces themselves are not used in any other calculations (such as shear capacity of columns or beams)?

can you treat a building as cantilevered from ground and the seismic forces are like distributed load.. and if you focus story forces to a single floor.. it's like a concentrated point load and the responding differences in the shear diagrams between the 2 load cases?

 

[hocho]

You're very welcome Hocho. By "cantilever", I meant that the beams and columns would be laterally restrained at their bottoms but not at their tops.

Did you mean "wall" instead of beam above? A typo? If not.. how can beam have top?

Walls that are tied into high and low diaphragms and adjacent columns will deliver some portion of their seismic load to all of those elements. Don't let yourself get confused about the fundamentals of load distribution simply because we're talking seismic. Recognize, however, that the wall load delivered to the columns still eventually ends up in the diaphragms that laterally restrain those columns

But if a structure is purely moment resisting frame and no shear wall or brace frames.. is your "diaphragms that laterally restrain those columns" still valid above? How can diaphragms restrain those columns if there were no shear walls or braced frames.. do you assume there are in my given example. So if there isn't.. then the slab diaphragms would go wherever the columns want them to go and be and there is no restraining?

 

[KootK]

It was a typo above. And yes, if your lateral system is moment frames, that would certainly alter the situation regarding what is restraining what.

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.