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Re: URM - Ledger Connection[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: URM - Ledger Connection
- From: Amaloyan <Amaloyan(--nospam--at)aol.com>
- Date: Thu, 18 Dec 1997 02:57:12 EST
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 mezzanine, 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 bolts have deflected at 1/8". You can test the specific product (min 5 bolts per wall) and use the test results. The building official in your jurisdiction may give you a modification based on 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 bolts 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 convince the owner to have an independent structural system to be built. Tell the owner when 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 ;0) Happy Holidays Ara Maloyan P.E.
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