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RE: Overhead anchors

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Be sure to check for prying effects caused by the baseplates flexing.  That was a big problem in the nuclear industry in the late 1970s - early 1980s.  At the time I was involved, flexible plate analysis showed that anchor bolts can be easily overloaded by factors of 3 or 4 on hanger baseplates as small as 12" x 12" x 1", which by eyeball would seem to be rigid.

Also, such bolts sometime lost their tension due to the concrete relaxing.  Adhesive failure is not the only source of problems.

----- Original Message -----
From: Roger Davis <rdavis(--nospam--at)sdsarch.com>
Date: Wed, 12 Feb 2003 10:02:07 -0600
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: Overhead anchors

> One of the easiest choices to make is to continue using your favorite 
> anchor but to increase the safety factor.  A representative of one of the 
> major expansion manufacturers told me he would use a safety factor of at 
> least 6 for non-critical loads and a safety factor of at least 12 for 
> critical loads.
> 
> Roger C. Davis
> Architect
> SDS Architects, Inc.
> 
> -----Original Message-----
> From:	Sherman, William [SMTP:ShermanWC(--nospam--at)cdm.com]
> Sent:	Wednesday, February 12, 2003 8:55 AM
> To:	SeaInt Listserver (E-mail)
> Subject:	Overhead anchors
> 
> Engineers in our office have expressed concerns with using expansion 
> anchors
> in overhead applications, such as hanger supports, due to the potential of
> long-term slippage under constant tension. I do not see any cautions noted
> on the use of expansion anchors in such applications in manufacturer's
> literature or in ICBO reports. Does anyone know if there is documentation 
> of
> slippage of "friction-type" anchors in constant tension applications?
> 
> We often prefer to use adhesive anchors in overhead applications, when
> drilled-in anchors are required - but concerns have also been raised with
> such anchors due to the potential softening of the adhesive in case of a
> fire. Also, overhead installation of adhesive anchors is more difficult.
> Does anyone have other recommendations for application of post-installed
> anchors in overhead applications?
> 
> 
> William C. Sherman, PE
> CDM, Denver, CO
> Phone: 303-298-1311
> Fax: 303-293-8236
> email: shermanwc(--nospam--at)cdm.com
> 
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