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RE: Anchor Rods for Friction Connection

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Thank you for taking the time to respond to my inquiry.  I appreciate your insight and recommendations.

I'm actually designing this connection to resist shear forces parallel to long slotted holes in the base angle of a transformer.  To keep the transformer from slipping due to the slot, I initially thought of a friction connection and, since resistance to slip is determined by the amount of bolt tension and the condition of the contact surfaces, I was trying to come up with a method to ensure proper bolt tension.

I have since redesigned this connection to include a plate washer with a standard-sized hole that will be welded to the angle, thereby eliminating the need for a friction connection. 

Thanks again,
Greg

>>> SpragueHO(--nospam--at)bv.com 10/11/00 02:21PM >>>

It sounds like you want to assure a definitive tension in the bolt.  If that
is the case you need to use a headed anchorage.  The F 1554 is the proper
spec for the anchor bolt.  You should tape wrap and grease the shaft to
assure no concrete bond.  That way you have a definitive length of rod.  

I would forget the A325 and A490 spec.  Turn of the nut should not be used
to apply tension to the bolt.  Turn of the nut can only be used on bolts
less than 12 dia in length, and it is not all that accurate.  It tends to
tension bolts on the high side.  If it happens to break it is not a big deal
if it is a normal bolt.  If it is an anchor bolt, you've got real problems.

I would design the bolt such that you only tighten the bolt for 50 or 60% of
the tensile strength, and I would use a direct hydraulic tensioner such as a
Biach tensioner.  That is what is done in many pressure vessels, ASME
structures, and in nuclear work.  An alternative is the direct tension
washers that are calibrated for tensions less than the A325 spec.

Locking the nuts is not necessary especially if you have designed the
initial tension to be greater than the service tension load.  I would also
require rechecking the tension as they do in the petrochemical industry.

Regards,
Harold Sprague


> -----Original Message-----
> From:	GREG DIAS [SMTP:GREGD(--nospam--at)mid.org] 
> Sent:	Wednesday, October 11, 2000 3:46 PM
> To:	seaint(--nospam--at)seaint.org 
> Subject:	Anchor Rods for Friction Connection
> 
> As a "newby" to this forum, please take it easy on me.....
> 
> I am in the process of specifying ASTM A449 or ASTM F1554 (Gr 105) anchor
> rods to connect a slotted angle base (for a large electrical transformer)
> to an isolated concrete pad in a Seismic Zone 4 location.  I have
> currently specified A563 Grade DH heavy hex nuts, F436 Grade 1 washers,
> with the surface condition of the bolted parts as "Class D", and a
> requirement to be in compliance with AISC "Structural Joints Using ASTM
> A325 or A490 Bolts" for ASTM A325N bolts as it relates to the friction
> connection.  I have also included the "turn-of-nut" method for proper bolt
> torque, along with a requirement that anchor rods be locked with a
> "Palnut" locknut, which "shall be installed by tightening 1/3 to ½ turn
> after the smooth side is seated finger-tight againast the hex nut".  
> 
> I would appreciate any input or recommendations that you may have to
> improve this specification.
> 
> Thanks   
> 
> Greg Dias, P.E.
> Sr. Civil Engineer
> California Certificate No. C 39501
> Modesto Irrigation District
> Ph: (209) 526-7566
> Fax: (209) 526-7352
> E-mail: gregd(--nospam--at)mid.org 
>