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Shearwalls with Split Stories

Shearwalls with Split Stories

Shearwalls with Split Stories

(OP)
Not really sure how to label this thread but if you view the image below I think you will get the idea that I am trying to convey:

http://design.medeek.com/images/misc/SPLIT_LEVEL.j...

I have a 70'x36' gable structure, with about 1/2 the floor space with an office framed at the 2nd level as shown. The designer wants to platform frame it, which I don't think is problem.

With regards to calculating the shearwall loads it seems to me that things become a little more interesting. Right off the bat I threw this into Woodworks software but was unable to figure out how to handle different wall heights in the same model, maybe someone else has come across this before and has a solution.

Another thing I noted was that the trib. area to the wall is actually increased where the structure has the 2nd level office floor. With 16' studs the trib. length is half the stud height or 8'. With the two floors at 8' each, the total trib. length from the wall is 8 + 4 = 12'. Nothing too groundbreaking but worth noting.

Calculating the loads to the shearwalls parallel to the ridge with shearwalls of different heights and on different levels has me a bit mystified at the moment but I'm sure it will all become clear shortly.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Shearwalls with Split Stories

I think that a good place to start would be to examine the penetrations in the side walls and determine whether or not you'll be stitching the two story and full height wall segments together into a single shear wall. If they will be stitched together, then the mezzanine just represents an additional seismic load and a modified wind load distribution. If not, it's a bit more complicated and you'd need to work out the load distribution to the different segments.

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.

RE: Shearwalls with Split Stories

(OP)
Both front and rear longitudinal walls will be stitched together at the change in stud height interface. I was really hoping shearwalls could handle this case but so far no such luck. That is the problem with relying too heavily on software, we become lazy and when something comes along that requires some manual work we are out of practice and inefficient.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Shearwalls with Split Stories

What if you imagine a collector at the mid height of the 16' studs. Run blocking and a strap. Consider the middle diaphragm as continuous.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Shearwalls with Split Stories

I wonder if you could consider the building to be either a single story structure or a two story structure at all locations and just adjust your weights/loads somehow to simulate the correct results.

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.

RE: Shearwalls with Split Stories

(OP)
This the response I received from tech support for the shearwalls software, pretty close to what KootK is suggesting:

Quote:

I am under the impression that you are trying to create a
shearwalls model of structure which has a loft. Unfortunately
shearwalls is not capable of exactly modelling the situation you are
suggesting in the sketch you provided, because as you are aware, you
cannot set blocks with different wall heights.

You are going to need to use your own judgment on the most appropriate
way to model a loft. Keep in mind that the shearwalls assumes platform
frame construction. To model the loft in the example you provided, I
would recommend creating two different models. One model where you
treat the loft as a storey which runs the full area of the structure
(Assume the loft is an additional storey, and the diaphragm is
continuous throughout the storey). This model will produce accurate
results for the areas where the loft is located. Then create a second
model where you neglect the loft completely, but specify the height of
the walls on the first storey to be the same height as the first model.
This should create accurate results for the walls where the loft is not
located. Finally, compare the results of both models and use your
judgment on an appropriate design.


A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Shearwalls with Split Stories

I'd treat it as single story. I'd look for some shear wall at that interior mezzanine edge.

RE: Shearwalls with Split Stories

(OP)
The actual layout is a bit more complicated than the simplified diagram above but as suggested by Triangled I do have interior shearwalls at the mezzanine edge.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

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