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Re: Brick-masonry shear strength

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1) A relationship between permissible shear strength and ultimate shear
strength is provided by the 1997 Uniform Code For Building Conservation
[available from ICBO,] provided the "ultimate" shear strength
is determined in accordance with Uniform Building Code Standard 21-6 [in
volume 3 of the 1997 UBC, also available from ICBO].

2)  There may not necessarily be significant frictional force available at
the contact of a brick masonry infill with the adjacent concrete frame --
Frame/infill analysis generally assumes a compression strut developing in
the brick between opposite corners of the frame, with the frame members
bearing on the corners of the brick infill as the frame deflects and
distorts under lateral load.  For procedures for seismic analysis of a
concrete frame building with URM infills, in seismic zone 4, see Chapter 95
of the 1999 City of Los Angeles Building Code, [also available from ICBO,
item No. 133A99 in their website product store].

3)  Poisson's ratio may not be a very useful concept in dealing with URM
construction.  It's a non-isotropic assembly of rigid bricks embedded in a
soft mortar.  I visualize the soft mortar absorbing most of the lateral
strain resulting from a uniaxial compression.  However, I'm not familiar
with any testing to establish a Poisson's relationship.  URM construction is
highly variable -- typical values should be held suspect.  Materials
properties of brick infills for use in the Los Angeles City procedure are
generally determined in-situ, using pairs of flat jacks inserted into mortar
joints to put a zone of wall into compression, in conjunction with strain
gages to develop stress-strain relationships.

Nels Roselund
Structural Engineer