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Re: UCBC97

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Yi,

My interpretation is that the wall thickness must comply with both
requirements: 18" minimum thickness and H/t in compliance with Table A-1-G.
You may be able to use a well bonded stucco on one or both sides of the wall
to increase the effective thickness; the plaster should be secured to the
wall by lath that is anchored to the wall with pins set in epoxy, or,
alternatively, rods that pass through the wall and anchor the lath on both
sides together through the wall; in this case epoxy embedment is not
required.

I think that you are required to have the bond beams.  Note, however, that
paragraph that requires compliance with Table A-1-G allows bond beams of
other materials to be used with the approval of the building official.  When
you get to the design phase, some creative details that take into account
the functions of a bond beam [some of which are stated in my previous email]
may lead to solutions that you prefer.  What usually comes to mind:
through-the-wall reinforced concrete bond beams would be very disruptive to
build at the second floor level, and may do irreparable damage to the walls
as you try to build them.  I've used some details to solve this problem that
I consider proprietary, but I may be able to give you some guidance to a
solution.

You made a good call in stating that there will be uplift on the top of the
wall from the diaphragm when it braces the wall against out-of-plane
separation.  Deeply embedded adhesive anchors [I usually have them installed
in sets of two, slanting downward and toward the opposite side of the wall]
are generally needed to develop enough weight of masonry below to hold down
the top of the wall.  I saw earthquake damage to the top of a wall that was
lifted by the diaphragm -- the horizontal crack was at about the level of
the bottoms of the anchor bolts because the anchors were not long enough,
and the wall had tilted outward under the crack.  You are right about the
advantage of a bond beam in this case: the adhesive anchors may be embedded
in the bond beam and the connections to the roof may be separate devices
that also connect to the bond beam, and the bond beam transfers forces
between them.  I don't know of any off-the-shelf way of solving this
condition.

Nels

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net



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