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RE: Coring concrete slab

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The building is four stories with 10 foot floor to floor heights and
vaulted spaces on the 4th floor!  It's pushing the limits.  The highly
loaded hold downs are double custom HD's (one on each side of a 4x14
post).  The 25,000# was just to give an idea of the magnitude the actual
maximum is about 15,000# per side for a total of 30,000# on a double HD,
sorry.  The forces are big, but what can you do if you are given an a
building that doesn't have a lot of long walls and sits on a concrete
deck.  

Thomas Castle, S.E.

> ----------
> From: 	Bill Cain, S.E.[SMTP:bcain(--nospam--at)ebmud.com]
> Sent: 	Wednesday, March 11, 1998 12:42 PM
> To: 	seaoc(--nospam--at)seaoc.org
> Subject: 	Re: Coring concrete slab
> 
> 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.
>  
> 
> _______________
> 
> BILL CAIN, SE
> OAKLAND, CA
> _______________
> 
> 
>