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RE: Reinforcing Masonry Shear Walls

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Use strength design!



-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)]
Sent: Thursday, August 28, 2003 7:02 AM
To: seaint(--nospam--at)
Subject: Reinforcing Masonry Shear Walls


The 1997 UBC rules for reinforced masonry shear walls provide allowable shear values for two conditions: masonry designed to resist all of the shear; reinforcing steel designed to resist all of the shear.  Rules for adding the masonry capacity  and the reinforcing capacity are not provided.  What is the reason for this?


I can imagine that the rules for designing reinforced walls include, hidden in the numbers, the masonry capacity; or else, there was uncertainty in the minds of the code writers concerning how to add the capacities.


I am designing the strengthening of existing unreinforced masonry shear walls.  Based on testing, I can establish the shear capacity of a URM wall on this project -- it is not enough, so I want to supplement  its shear capacity with reinforcing.  In the past, I have done this by applying portland cement stucco with welded wire mesh reinforcing, based on some research done in the 1960's for strengthening URM public school buildings in Los Angeles.  My current project is on a historic building for which it is desirable to avoid adding finishes to the walls.  For that reason, I am looking into the Cintec system, which installs steel rods into the walls, embedded in cementitious grout injected into holes that are drilled the length of the walls.  Every piece of reinforcing is a big deal because of the drilling operation, so I want to do whatever is reasonable to minimize the amount of  reinforcing that needs to be installed.


What will be sacrificed by adding the shear strengths of the masonry and the reinforcing?


Nels Roselund
Structural Engineer
South San Gabriel, CA