Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: hooked ABs and ABs with bearing plates

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I believe that the ACI 349 anchor bolt embedment method used to require that the tensile area of the pullout cone be reduced by the area of any bearing plates provided at the head (not sure if the current provisions address this).  As Harold noted, research showed that bearing plates could be detrimental because of reduced bond to the concrete below the bearing plate.  Bearing plates were provided mainly to reduce bearing stresses at the head - but research has shown that a standard bolt head is adequate to develop the anchor in tension via bearing on concrete.  This does create high bearing stresses which also have a lateral component, requiring adequate side cover.
As with others, I then stopped using bearing plates at embedded anchor bolts - also stopped using hooked anchor bolts, since headed bolts were found to perform better. 
Bill Sherman

From: Harold Sprague [mailto:spraguehope(--nospam--at)]
Sent: Wednesday, August 06, 2008 8:37 AM
To: seaint(--nospam--at)
Subject: RE: hooked ABs

Most of the research I have seen is a mixed bag.  Most of the research used hex heads. 
I have a fundamental problem with increasing Abrg and that has to do with the required stiffness of the bearing plate.  In order to be effective, the thickness gets huge.  TVA performed some studies many years ago that fed into the ACI 349, and they found bearing plates to actually reduce the pull out strength. 

Harold Sprague

From: Suresh.Acharya(--nospam--at)
To: seaint(--nospam--at)
Subject: RE: hooked ABs
Date: Tue, 5 Aug 2008 10:23:11 -0700

Harold & Andrew,
Are not the ACI Appendix D formulas specifically intended for standard welded headed anchors because the tests were done on these type of anchors? In the formulas, edge distances are measured from free edge to the center of bolts. Formulas give substantially greater pull-out and side-face blowout capacities if "Abrg" is increased (i.e. by using bigger washer plates), but the distance to the face of head/washer from free edge is never a variable in the formulas. Does that mean "Abrg" should be limited to the standard areas from PCI handbook in calculations, and the thickness of plates should match the standard thickness of heads?
Also, any oversized hole in the plate may affect the shear capacities.
Suresh Acharya, S.E.

From: Andrew Kester, PE [mailto:akester(--nospam--at)]
Sent: Tuesday, August 05, 2008 8:26 AM
To: seaint(--nospam--at)
Subject: re: hooked ABs

I agree with Harold, I have never heard anything great about hooked ABs though they are still used all over the place. My boss stopped using them when I first started out of college about a decade ago because he read they "would fail by 'snaking' out of the house (wait, how did that much time just slip by!)...
Simpson in Jacksonville, FL (may have something sim. in TX or CA) has a one day seminar regarding their epoxies, bolts, etc. With audience participation, they drill holes in a big block of concrete and then after lunch you test them, even the epoxy anchors. Great demonstrations, as the epoxy would either shear cone fail the concrete or fail the rod in tension. The hooked L bolts always "snaked" out of the hole with the L straightening out.
If we have a connection at a foundation in particular, with any kind of uplift, we use all-thread rods with two nuts and a 2" SQ washer at the end. Nobody ever complains but if they do Simpson makes a PL1/4x2x2 I have seen at Home Depot. For really big uplift conditions at footings we will sometimes make those washers bigger or just use an embed plate that would have to fail in punching shear. We usually detail a couple of pieces of rebar sitting on top of the plate for a little feather in our cap.
Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Drive, Suite 301
Orlando, FL 32803

Get more from your digital life. Find out how.