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RE: Grade @ Anchor Bolts

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My understanding is that the plate washers on anchor bolts were found to
essentially create a plane of weakness at the plane of the plate washer
(i.e. acting as a bond breaker). Thus the plate washer moves the failure
cone out from the centerline of bolt to the perimeter of the plate but the
area of the plate washer is considered to have no tensile strength. The
crack will follow the path of least resistance - i.e. a horizontal plane at
closely spaced washer plates (or near an edge). Since the plate washer does
little to add strength and can be detrimental for anchor bolt groups, anchor
bolts without plate washers are preferred. 

A high bearing stress does occur in the vicinity of a standard headed anchor
loaded in uplift. However, testing has shown that the bolt strength will be
developed as long as the bolt head is adequately confined, e.g. has adequate
edge distance to avoid lateral bursting. The lateral bursting force is
considered to be 25 percent of the bolt tensile force. 

> -----Original Message-----
> From: PEC - Lake City [mailto:pec(--nospam--at)isgroup.net]
> Sent: Friday, August 18, 2000 2:00 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Grade @ Anchor Bolts
> 
> 
> Charlie,
> 
> Does the "chunk" behavior apply just to multiple anchor bolts 
> connected to a
> single plate or would it also apply to anchor bolts each 
> having its own
> individual plate (such as a plate washer) acting in group behavior?
> 
> David Finley, P.E.
> 
> 
> -----Original Message-----
> From: Charlie Carter <carter(--nospam--at)aiscmail.com>
> To: 'seaint(--nospam--at)seaint.org' <seaint(--nospam--at)seaint.org>
> Date: Friday, August 18, 2000 12:03 PM
> Subject: RE: Grade @ Anchor Bolts
> 
> 
> >>>...headed or threaded/nutted embedments
> >>> can be fully developed with the head/nut only by 
> selecting the proper
> >>> embedment (length).....adding a plate at
> >>> the bottom of the embedment introduced a plane of weakness in the
> >concrete
> >>> that REDUCED the strength of the embedment!
> >
> >>Can you (or someone else) please elaborate on this
> >>particular topic / mode of failure?
> >
> >With a head or nut (but no plate) at the end of the 
> embedment(s), the mode
> >of failure on anchorage devices is a cone-type failure in 
> the concrete,
> >assuming that limit state is the controlling limit state. 
> The intersection
> >of cones often reduced the total strength of the embedment 
> group, but you
> >can still count on a cone-type failure.
> >
> >With a plate at the bottom of the anchors, the mode of 
> failure is likely to
> >change from a lot of individual cones to one big chunk 
> (technical term)
> with
> >a flat bottom. If so, and since this has less surface area, 
> it reduces the
> >strength.
> >
> >Charlie
> >
> 
> 
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