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Re: URM - Ledger Connection

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Dear Dennis:

If I were you I would  (NOT) add any more vertical loads to the URM
walls. If you remember City of Los Angeles does not allow additional
loads to be imposed on the existing system. If that was not the case 
you would see new additions on top of existing URM walls.

I would support the entire mezzanine independently for vertical and
lateral loads. By connecting the walls for out of plane loads to the
you are also introducing in plane shear loads into the wall.
The 22 1/2 anchor bolts do transfer shear and tension by virtue of
their geometry and use of epoxy.

The answer to your question regarding actual shear capacity of a 3/4" threaded
rod imbedded 8" into the URM wall is:
Depending which epoxy system you use Covert or Hilti or Epcon you will get
4000 to 5000 lbs shear capacity. The normal safety factor
is (5) for connections at ultimate capacity or (3) for values achieved when
have deflected at 1/8".

You can test the specific product (min 5 bolts per wall) and use the test
The building official in your jurisdiction may give you a modification based
the test results. The other item that may be a factor is the bearing capacity
of a 
URM assembly. If I remember correctly 100 psi was the magic number. 

100 psi was used to get the prescriptive sizes like 6x6 plates for the tension
and 4x4 angles 12" long for transfer of wall tension loads into the diaphragm.

The bottom line is do not connect the new mezzanine to the URM walls and
the owner to have an independent structural system to be built. Tell the owner
an earthquake hits to run and hide under the mezzanine, since the only thing
left standing after a long and hard shaking would be  the new structure

Happy Holidays 

Ara Maloyan P.E.