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 -----
Sent: Monday, October 21, 2002 9:39
Subject: Masonry Shear walls
This question pertains
to CMU walls used for back-up to masonry brick.
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
Terry Triest, EIT