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RE: plate washers on anchor bolts

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Paul,

If you use a deformed bar for the shaft you completely change the failure mechanism.  Headed anchor bolts assume the bond has been broken along the shaft and then the head bearing initiates the shear cone.  Deformed rods rely on continuous bond along the shaft and produce a much different pull out failure.

There has been enormous amounts of anchor bolts testing especially back in the old Nuclear days in particular by TVA.  ACI 349 Appendix B from the mid 1970's and early 1980's was the first American document to develop the whole shear cone failure analysis and was based on all this extensive testing which included plain heads, plates, and washer.  In the original shear cone failure design you had to delete the plate area from the projected cone area so you lost some of your capacity plus the shear cone starts at the edge of the plate so the cone can intersect the edges of your concrete if you are near an edge and therefore not fully develop the cone.

Both the current ACI 318 Appendix D and the previous ACI 349 Appendix D clearly show that a plate washer is unnecessary.

Thomas Hunt, S.E.
Fluor



From:        "Thor Tandy" <vicpeng(--nospam--at)telus.net>
To:        <seaint(--nospam--at)seaint.org>
Date:        11/17/2010 09:39 AM
Subject:        RE: plate washers on anchor bolts




Do you have some examples of “harm”?  Large numbers of washer/plates?  I would have thought that closely spaced washers/plates would encourage a single plate type of embedded.  The analysis of anchors seems to suggest a “bearing” face so the washer/plate concept is a natural kneejerk good idea … ?  
 
I sometimes wonder if our anchoring bolts/rods should be a combination of rebar-type deformations plus a head … a kind of developed length plus mechanical anchorage.  Has anyone seen any published research with this idea?
 
Here, we no longer refer to the anchors as “anchor bolts”, simply as “anchors” or “anchor rods”.
 
Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE, MSCSE
Victoria, BC
Canada

 
 
 
From: Tom.Hunt(--nospam--at)fluor.com [mailto:Tom.Hunt(--nospam--at)fluor.com]
Sent:
Wednesday, November 17, 2010 6:54 AM
To:
seaint(--nospam--at)seaint.org
Subject:
Re: plate washers on anchor bolts

 
Paul,

This has been an issue for many years.  You are absolutely correct that the large plate washer at the bottom of a headed anchor bolt can actually cause more harm than good.  I think there are those who feel uncomfortable with relying on just the head of the bolt or tack welded nut and think the plate washer is just a good "belts and suspenders" approach.


Thomas Hunt, S.E.

Fluor




From:        
PFFEI(--nospam--at)aol.com
To:        
seaint(--nospam--at)seaint.org
Date:        
11/17/2010 05:17 AM
Subject:        
plate washers on anchor bolts






I am curious why some engineers install plate washers on the embedded ends of foundation anchor bolts.  The headed deformation of a heavy hex nut is enough to develop F1554 grade 36 rods in tension (per ACI Appendix D calculations) and AISC Column Base Plate Design Guide also shows nut sufficient to develop rod. It would seem that plate washers could be detrimental in closely spaced anchors - they could cause cracking through failure plane interconnecting plate washers.  Does anyone have any information on this practice?

 
Thanks- Paul Franceschi

 
 
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