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Re: Strength Design of Masonry Wall (per UBC)

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Bill,
 
You calculation looks right, but let me ask a dumb question.  How tall is your wall?  I am thinking that your wall would have to be relatively short for shear to govern...and then I am not sure why would would need #6 @ 8" for a shorter wall, but I might be missing something.  I will suggest something...keep in mind that I don't intent to insult your intelligence or anything like that, but just making an observation from the limited information that I have...the question that comes to my mind is...did you neglect to remember that your answer is per foot of wall?  In otherwords, don't forget that it is 2543 lbs/ft of "allowable" shear NOT 2543 lbs of "allowable" shears for the entire width of wall (unless your wall is only 12 inches wide).  I apologize if I am missing something completely...just trying to help.  :-)
 
Regards,
 
Scott
Adrian, MI
 
-----Original Message-----
From: Bill Allen[mailto:t.w.allen(--nospam--at)cox.net]
Sent: Monday, July 2, 2007 2:19 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Strength Design of Masonry Wall (per UBC)
 

I would like a confirmation that I知 looking at out of plane shear strength correctly.

 

Wall thickness = 8 in. (nominal)

Solid Grouted

F知 = 1,500 psi

b=12 in.

d=5.25 in.

Ae=91.2 in2 (from the equivalent solid thickness)

#6 bars at 8?/SPAN>

Temp. & Shrinkage horizontal steel

 

Mu/Vud >1, Cd=1.2, Vm(max)=63CdAe=63(1.2)(91.2)=6,895 lbs.

Vm=CdAe√F知)=(1.2)(91.2)√(1,500)=4,239 lbs. < 6,895 lbs.

Vs = 0 since ρn = 0 (no shear reinforcement)

Vn = 4,239 lbs.

φv = 0.6

φv Vn = (0.6)(4,239) = 2,543 lbs.

 

Is this right?

 

If so, shear is limiting my design using strength design and it didn稚 come anywhere close using working stress design.

 

TIA,

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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