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RE: Masonry Shear walls

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  Thanks to all who commented.   It looks like we are going to reassess our design procedures for CMU back-up.
-----Original Message-----
From: Paul Feather [mailto:pfeather(--nospam--at)]
Sent: Monday, October 21, 2002 1:40 PM
To: seaint(--nospam--at)
Subject: Re: Masonry Shear walls

If you are using the cmu wall to support a masonry veneer for out of plane loads, you design the cmu and the connection to the diaphragm levels for the out of plane load, wind and seismic.  This is an engineered solution not a pre-tested assembly.
RAM is an analysis program, therefore you are most likely designing a steel frame structure.  If you provide CMU walls the RAM analysis is worthless without accounting for the interaction of the shearwall system and the frame system based on geometry and relative stiffness of the systems.  With no intention of sounding sharp, RAM is only a computer program and is incapable of performing a valid lateral analysis.  The validity of the analysis will depend on the correct modeling of the structure for the actual anticipated behavior, and the addition of rigid elements cannot be ignored or neglected, or arbitrarily assigned some value of lateral resistance.
You must either determine the load the walls will share based on a rigidity analysis and detail the CMU for the resulting forces as well as the diaphragm connections to the CMU, or you must separate the CMU from the structure for lateral load.  Is this a brace frame or a moment frame structure? If this is a moment frame structure the masonry may reach failure mode prior to the moment frames generating sufficient displacement to resist the lateral loads.
The interaction of these systems will be one of the critical detailing elements for the structure.  You should sit down with one of the senior engineers in your firm and establish a proper system for analysis, both for the desired behavior and the proper detailing to ensure the desired behavior can be achieved.
----- Original Message -----
To: Seaint
Sent: Monday, October 21, 2002 9:39 AM
Subject: Masonry Shear walls

This question pertains to CMU walls used for back-up to masonry brick.    How much capacity does CMU back-up distribute to the structural frame?  
Does anyone have information on the testing of this assembly?
I use RAM and was wondering if (how much) I can rely on the CMU for lateral resistance.

Terry Triest, EIT
Structural Engineer
P: 814-940-4041
F: 814-949-2644