Wood Shear Wall Sitting on a Beam

[otto_eng]

Hi ,

I am an EIT working on a project and some of the shear walls are sitting on beams on 2nd floor because they are not lining up with shear walls below. Since there is an overturn at the shear walls it is causing compression and tension on the beam so I am designing the beams to bear these loads.
I am designing the beams on StruCalc and there is no option for seismic load choice. Do you guys think that would be okay to consider these compression and tension forces caused by seismic force on shear wall ,as a live load just for the sake of beam design ?

Thank you,,

 

[kipfoot]

I don't use strucalc, but your approach to the beam design seams reasonable.

(I'd suggest you delete your other post about this because this one explains your situation better, in my opinion)

 

[wannabeSE]

I don't know if StruCalc uses ASD or LRFD (I would guess ASD). Once you figure this out, scale the loads by looking at the appropriate load combination. If ASCE 7 is the standard for the seismic loads, don't forget to use the oversrength factor on the seismic loads per §12.3.3.3.

 

[XR250]

If the beam is long, deflection may control anyway.

 

[slickdeals]

Depending on the magnitude of the moment relative to the gravity load, pay close attention to the connection at the beam ends. Also, don't forget the overstrength factor for the member and also need to design the diaphragm to transfer the loads to the offset shear wall.
Make sure you check all the elements in the load path.

 

[otto_eng]

Thanks for the responses.
@slickdeals I am not clear about designing the diaphragm to transfer the loads to the offset shear wall. Could you please elaborate it ?

Thank you so much !

 

[slickdeals]

If you have an offset shear wall condition, i.e., your shear wall terminates at a floor, then you are taking care of the overturning moments through the beam and columns.

You also have a shear that has to be transferred to adjacent walls. Refer to 12.10.1.1 that talks about adding the transfer shear.
Imagine the diaphragm as a beam spanning between the walls on the 1st floor. This beam will have a point load equal to the shear in the wall you are stopping. You should design the diaphragm not only to cater to the force that it has at the 2nd floor but also this transfer shear.

Figure out what your shear is on the 2nd floor diaphragm. This would give you a unit shear w1.
Then figure out the additional shear coming from the wall stopping at the 2nd floor. Distribute this shear based on a simple beam analysis and you will get a unit shear w2.
The connection of the diaphragm at the 2nd floor should be designed for w1 + w2 (if you are not using over-strength factor, then you will need to amplify w2 by 25%, assuming you are in seismic design category D or higher, per ASCE 7 Section 12.3.3.4)

The below link walks through in detail.

http://www.woodworks.org/wp-content/uploads/2015-Workshop-Advanced-Diaphragm-Analysis.pdf

 

[KootK]

As far as the program use goes, you just need to do this:

1) Figure out the factored load being delivered to the beam from the wall.
2) Adjust the load entered into your software so that, when it's fudge factored as live load, the result is the same.

Defining your lateral bracing may be important here since you may induce compression in the bottom flange.

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.