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Re: Coring concrete slab

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At 14:28 3/10/98 -0800, Tom Castle wrote:
> Help! ...
>	I am working on a seismic retrofit of a group of residential
>timber framed buildings over a mild reinforced concrete parking flat
>slabs.  We are adding a lot (over 1,000) hold down rods through the
>deck.  Our plans show drilling through the 12 inch slab and placing a
>square plate washer on the underside of the slab.  The project is
>located in the City of Los Angeles.  I mention this fact because I
>believe this precludes the option of using epoxy anchors into the slab
>due to the low allowable values in the City and the relatively high
>loads (as much as 25,000# tension).  I specified on the plans to verify
>by nondestructive means the rebar location before drilling.  I did not
>want to cut any rebar because the slab appeared to need all it could
>get, specially with the new loads that could be imposed on it.  .....  

[Bill Cain]  Am I missing something or does 25,000# seem like a high hold
down force to use on typical timber framing (e.g., assuming a three story
structure, 8 foot story heights, that would be over 1,000 lbs per foot
required to be developed at the connection between the sheathing and the
end post).  The tension plus bending on the end post with any normal
eccentricity would also be substantial.  If it is a double hold down
installed symmetrically, that would translate to 50,000# (25,000# per
anchor bolt) at that location.  Developing that with a 12" slab and through
bolts with plate washers would not seem to provide a ductile (i.e., bolt
yielding before the anchorage fails) connection.