# Seismic Force on Walls



## MOOK (Jul 9, 2009)

In ASCE, the seismic force on walls is

F = 0.4 X I X SDS X W

and Seismic force on the Anchorage system in the wall is

F = 0.8 X I X SDS X W

I noticed that Allan Williams in ALL his books, used the follwoing fourmual for seismic force on walls

F = 0.8 X I X SDS X W instead of F = 0.4 X I X SDS X W

Can anyone explain why??

Thanks


----------



## McEngr (Jul 10, 2009)

MOOK said:


> In ASCE, the seismic force on walls isF = 0.4 X I X SDS X W
> 
> and Seismic force on the Anchorage system in the wall is
> 
> ...


Mook,

I don't have my ASCE 7 in front of me, but I believe that section 12.8 gives the criteria for this. They are different for seismic design categories. Also, the minimum out of plane wall load is 280 plf... it's an old UBC provision that has "stuck" throughout the years.

BTW~I'm on vacation right now, so I guess I've admitted how much of a loser I am... don't have the benefit of using the code to site specifically, but hopefully I've gotten you close to the answer you need.


----------



## kevo_55 (Jul 10, 2009)

Mook,

Can you give some specific examples? If the 0.8Sds*I*Wp equation is being used he most likely is just using that to calculate his anchorage requirements and not wall requirements.

Thanks.


----------



## MOOK (Jul 10, 2009)

McEngr

What you said is applied for Anchorage but not for walls. Walls have only one equation whatever the SDC or the diaphragm type. Based on my understanding from ASCE.

Kevo_55

Seismic and Wind Forces Structural Design Examples, 3rd edition, ICC Publication

Example 5.4 page 346, Again he used 0.8 instead of 0.40

Example 6.6 Page 467, Allan used 0.8 to design the wall instead of 0.4

Civil &amp; Structural Engineering Seismic Design Review for the PE Exam, 6th edition. One of Allan Williams books by Kaplan.

Example 5.5 page 298 bottom of the page, Allan used 0.8 to design the wall (NOT THE ANCHORAGE)

Am I missing something?


----------



## kevo_55 (Jul 11, 2009)

mook,

You're not missing anything. I have the 2nd edition of the seismic and wind forces book and it is an error. This is Williams at his best. He calculates his members quite conservatively yet it is not per code.

Realize that it is an error and continue on.

Do you happen to have the SEAC/SEAOC/ICC 2006 Structural/Seismic Design Manual Volume 1? It goes through this topic quite well.

I hope this helps!


----------



## MOOK (Jul 11, 2009)

kevo_55 said:


> mook,
> You're not missing anything. I have the 2nd edition of the seismic and wind forces book and it is an error. This is Williams at his best. He calculates his members quite conservatively yet it is not per code.
> 
> Realize that it is an error and continue on.
> ...


Kevo_55

Thanks for your reply.

I noticed that in the ICC Volumes but I was surprised that Allan did this mistake not in one or two problems but in all the problems in his books.


----------

