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Re: URM

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Mark,
It's been a few years since I retrofit a multistory URM, however in my time
I retrofit over 350 of them throughout Los Angeles. In all of these, we
never questioned the ability for the lintle to transfer the load from the
URM to the moment frame. The only thing that we did to assure appropriate
drag was to tie the lintles together at the pilasters with welded plates and
to add secondary supports below the lintles adjacent to the pilasters to
pick up the load if the pilaster fails.
This method, by the way, allowed more load to transfer throught the URM wall
(in plane) to the frame than through the capacity of the floor diaphragm
alone. Just be sure to get your beam as close to the lintle as possible to
minimize the eccentricity and any potential for plate buckeling.
One other thing I remember doing is to weld the plate at the bottom flange
of the beam to the bottom flange of the lintel and to use concealed anchors
welded from the top flange of the moment frame into the URM wall (or even to
weld anchors to the web of the lintle and the top flange of the moment
frame) which will help to brace the top flange of the beam.

There have been a few changes in Los Angeles over the last few years and I
understand that Vee straps are no longer allowed - opting for installation
of HD's in line with the blocking or joist (and one on each side).
I never understood this philosophy since the conventional V strap performed
well in Northridge as long as the strap was set tight (by blocking the strap
to take the play out of it).

Dennis Wish PE