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RE: Masonry Shear Wall

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I believe this is basically dealing with the concept that your shearwall can be dominated by flexural behaviour (i.e. a tall skinny wall) or by shear behaviour (i.e. a short squat wall).  If it is the latter, then there will not likely be enough flexural stress to cause a flexural crack, which would likely occur at a bond interface.  With little likihood of a flexural shear crack, then you can count on shear strength contribution from both reinforcing and masonry (since the masonry is not cracked).  In the former, if the wall is dominated by flexural mode, then it is likely that the flexural stresses have gotten large enough to create flexural cracks.  As a result, you cannot rely on the masonry to carry any of the shear and shear will only be resisted by the reinforcement.
 
So, the test is as Al offered...you figure out the nominal flexural strength (i.e. nominal moment capacity) and then determine how much shear would be in the wall at the point where the nominal flexural strength occurs.  If the nominal shear strength exceeds that value, then thought is that you will have enough cracking due to flexure to not count on the masonry in shear (keep in mind that unlike a typical beam, both sides will be cracked as the seismic load will have load reversals where a beam would only have cracks on "one side" due to typical gravity loads).  If it does not exceed that value, then you can count on both the masonry and reinforcement to take the shear.
 
At least, that is how I am seeing it.
 
Regards,
 
Scott
Adrian, MI


From: Grathwol, Albert [mailto:albert.grathwol(--nospam--at)aecom.com]
Sent: Thursday, August 13, 2009 5:38 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Masonry Shear Wall

That is the shear that exists in the element when the section is at it's limit of flexural strength.
Al


From: Doug Mayer [mailto:doug.mayer(--nospam--at)taylorteter.com]
Sent: Thursday, August 13, 2009 2:30 PM
To: seaint(--nospam--at)seaint.org
Subject: Masonry Shear Wall

All,

 

Section 2106.5.2 of the 2007 CBC limits the shear strength of a masonry shear wall where a shear wall’s “…nominal shear strength exceeds the shear corresponding to development of its nominal flexural strength…”  Where this is true, the allowable shear strength of the wall is limited to the reinforcing with no contribution from the masonry.

 

 I’m having a bit of trouble understand the last part of that statement (shear corresponding to development of its nominal flexural strength) and would appreciate a little enlightenment if anyone can spare some.

 

TIA,

 

Doug Mayer, SE

Structural Engineer