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Re: Masonry Half Stresses

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It's been a while since I've done any strength design masonry, but I do
remember that when the strength design method was first introduced, special
inspection was not required.  If you did not use special inspection, you
used a lower phi factor to compute the design capacity of the wall.  My
copy of Jim Amrhein's "Reinforced Masonry Engineering Handbook, 4th Ed."
uses a phi factor of 0.5 if no special inspection is preformed, and 0.8 if
it is preformed.  All other properties remain the same for the design, i.e.
use the full f'm value.  This method is also covered in a publication
titled "Design of Reinforced Masonry Tall Slender Walls", coauthored by
Amrhein and Donald Lee and published by the Western States Clay Products
Association in 1984.  I think that WSCPA either changed their name or
merged with another organization, so you might have some problems running
that last publication down.

--Kipp Martin, S. E.
  Portland, Oregon

Jake Watson wrote:

Strength design of masonry seems to give slightly more economical answer
than working stress design, especially for tall walls.  I am evaluating an
existing building that wasn't special inspected and would like to extend
half-stress concept to strength design.  I am doing this by using half of
f`m for calculating moment capacity but allowing full steel stresses.  This
effectively doubles the depth of the Whitney stress block in the moment
capacity calc while using only half the allowable stress.  The impact of
this approach seems to be a smaller penalty than using half-stresses for
working stress.  Translation, I seem to be getting relatively stronger
with strength design over working stress.

Has anyone else tried this or do you have any thoughts on this approach?  I
realize this is inconsistent with the original design procedures but it
seems rational to me.  Am I missing anything else?

Jake Watson, P.E.
Salt Lake City, UT

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