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RE: basic lateral force question

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When I have had rigid frames combined with shear walls I have calculated the deflection of each under a hypothetical lateral load (say 1 kip or 10 kips). I then simply use the inverse of this deflection as the rigidity of each element.

You are right that the shear walls will take most of the load. It is hard to make a rigid frame anywhere near as rigid as a shear wall.


Adam Vakiener, P.E.
Structural Engineer
Southern A&E, LLC

From: "Andrew Kester, P.E." <akester(--nospam--at)>
To: "seaint" <seaint(--nospam--at)>
Subject: basic lateral force question

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3 story office building with some CMU reinforced shear walls along the =
core of the building. On the second floor the floor extends out beyond =
the CMU walls on the north and south sides to have covered parking. =
Project in Florida, ZERO SEISMIC but 120mph wind.

A rigid diaphgragm (floor) of either a hollow core slab system or deck =
and concrete on steel joists.

I can use steel moment frames at the very N and S sides of the building, =
and then at the middle I will use some of the CMU shear walls and =
elevator/stair cores.

I have the SDI Manual and have been looking through it. Are there any =
limits on diaphgram cantilever I should be aware of (other than =
allowable shear force limits and deflection)? Both with steel deck, conc =
and steel deck, or hollow core? I am thinking with hollow core I may =
need to increase the 2" topping and provide a reinforcing mesh in excess =
of what we normally would do for gravity and normal shear...

Also, if I go the moment/braced frame route, how do I distribute the =
story shear between CMU walls and the frames? With the rigid diaphgrams =
at the floors I would normally assume this is a function of the rigidity =
of each shear wall and frame. Or can I just use trib area method? I know =
how to do this with all CMU walls, but how do I calc relative rigidities =
of CMU walls and steel frames? I am thinking the CMU walls are going to =
be MUCH stiffer than the steel frames, so that the steel frames would =
not see much of the load... I am talking about doing a torsional shear =
analysis to distribute the shear forces, but with a mixed system I am =
not sure how that would work. CMU- been there, done that, may go that =
route if possible.

Kind of need a starting point here because I think I can do it a few =
different ways.

Thanks in advance,

Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Ave., Suite 301
Orlando, FL 32803

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