Shear Walls

[MOOK]

Wood/Timber Shear walls:

In order to determine the seismic force due to self weight of the shear wall, should we include the total weight of the shear wall or only HALF of its weight.

I noticed that Allan Williams uses the whole weight of the shear wall except when he determines shear wall deflection, he uses half the weight. I really do not know why??

Concrete/Masonry Slender Shear Walls

In designing Concrete/Masonry Slender Shear Walls, do we include live load to determine Moment due to eccentricity but we should not include the live load to determine Moment due to P-delta effect, is that right??

 

[McEngr]

Wood/Timber Shear walls:In order to determine the seismic force due to self weight of the shear wall, should we include the total weight of the shear wall or only HALF of its weight.

I noticed that Allan Williams uses the whole weight of the shear wall except when he determines shear wall deflection, he uses half the weight. I really do not know why??

Concrete/Masonry Slender Shear Walls

In designing Concrete/Masonry Slender Shear Walls, do we include live load to determine Moment due to eccentricity but we should not include the live load to determine Moment due to P-delta effect, is that right??

V is the base shear which should equal the sum of all the story shears. In my Donald Breyer book (the best timber design book on the market) the bottom story is the entire height.

Also, for your concrete question: P-D effects are usually separated by moments due to gravity and moments caused by lateral design. The moments are magnified for the "beta" part of the equation. If you have a good concrete textbook, this will be pretty clear. For instance, when you work out the NCEES practice problem for the first question (problem 250), the moment magnification is zero for the gravity load and not zero for the wind design. Does that make sense?

 

[McEngr]

V is the base shear which should equal the sum of all the story shears. In my Donald Breyer book (the best timber design book on the market) the bottom story is the entire height.

Also, for your concrete question: P-D effects are usually separated by moments due to gravity and moments caused by lateral design. The moments are magnified for the "beta" part of the equation. If you have a good concrete textbook, this will be pretty clear. For instance, when you work out the NCEES practice problem for the first question (problem 250), the moment magnification is zero for the gravity load and not zero for the wind design. Does that make sense?

I should clarify that the Breyer book is also working out of the vertical distribution of seismic forces as elaborated in the ELF procedure, not simplified. Just an FYI...

 

[MOOK]

Thanks McEngr for your answers

* Regarding the timber shear walls. I am not asking about the total base shear. I am asking about the seismic force due the self weight of the shear wall. In Breyer book, example 10.5 page 10.16 and 10.17 you may see what I am asking about it.

* Regarding the concrete shear walls. I am not asking about moment magnification. I am asking about the moment due to vertical live load, do we include it on the wall design (moment calculation) or take the dead load only with the later loads

 

[McEngr]

Hi MOOK,

I'm so sorry. I misread your question. After reading again, I see that you are talking about P-Delta in relation to out-of-plane wall forces. I can't believe that I missed that! I'll check it out tomorrow and see if I can answer for you. I want to double check with my SEAOC VOL III seismic design manual for the 2006 IBC. I believe that the answer is that the magnified moment is applied to all aspects of the effects of the forces, thereby magnifying to the combination which controls axial+bending. This will usually be the 1.2D+f1L+E, where E is the magnified moment. f1 is either 0.5 or 1.0 I believe, but I'll check as I said, tomorrow.

Do you have a particular example that's throwing you or are you trying to put in scenarios for the exam?

 

[MOOK]

Hi MOOK,
I'm so sorry. I misread your question. After reading again, I see that you are talking about P-Delta in relation to out-of-plane wall forces. I can't believe that I missed that! I'll check it out tomorrow and see if I can answer for you. I want to double check with my SEAOC VOL III seismic design manual for the 2006 IBC. I believe that the answer is that the magnified moment is applied to all aspects of the effects of the forces, thereby magnifying to the combination which controls axial+bending. This will usually be the 1.2D+f1L+E, where E is the magnified moment. f1 is either 0.5 or 1.0 I believe, but I'll check as I said, tomorrow.

Do you have a particular example that's throwing you or are you trying to put in scenarios for the exam?

Hi McEngr

Actually all the references I have including ICC V.2 and 3 do not provide Live in the problem which makes you do not know if you should include the live load or not.