Lock washers on A325 bolts?
Lock washers on A325 bolts?
(OP)
I was recently told that lock washers (a.k.a. split washers) were not allowed on A325 structural bolts. Their reasoning was the following in AISC's 9th Ed. of ASD (page 5-266):
"(e) Washers. Flat circular washers and square or rectangular beveled washers shall conform to the current requirements of ASTM Standard Specification for Hardened Steel washers, ASTM F436"
This reads to me that FLAT & BEVELED washers must be hardened steel washers, but I don't read this as a prohibition on lock washers. I can't understand why a contractor should remove these washers, particularly after seeing a recent failure due to ineffective Anco (lock) nuts.
Any opinions, preferably backed by spec.?
"(e) Washers. Flat circular washers and square or rectangular beveled washers shall conform to the current requirements of ASTM Standard Specification for Hardened Steel washers, ASTM F436"
This reads to me that FLAT & BEVELED washers must be hardened steel washers, but I don't read this as a prohibition on lock washers. I can't understand why a contractor should remove these washers, particularly after seeing a recent failure due to ineffective Anco (lock) nuts.
Any opinions, preferably backed by spec.?





RE: Lock washers on A325 bolts?
RE: Lock washers on A325 bolts?
"...seeing a recent failure due to ineffective Anco (lock) nuts."
Could you fill in the details or point us to the story on this failure?
RE: Lock washers on A325 bolts?
RE: Lock washers on A325 bolts?
thread404-94197
thread725-85323
thread725-63343
thread725-57042
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Lock washers on A325 bolts?
I have inspected close to 800 telecommunications towers and have seen lock washers in many, many instances. In this case, I'm not really interested in opinions on their effectiveness, but in the requirements of AISC.
jheidt2543 - sorry, I can't give you details at this time, other than the bolts were loaded in tension and appear to have developed fatigue cracks prior to failure.
RE: Lock washers on A325 bolts?
Sorry that the previous threads weren't what you wanted. I don't think you will find what you want. The definition in your first post could be interpreted as excluding split washers.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Lock washers on A325 bolts?
I am not interested in opinions on their effectiveness, but I welcome opinions/interpretation of AISC requirements.
Thanks.
RE: Lock washers on A325 bolts?
My interpretation of AISC is that it allows only flat and angled washers to the exclusion of lock washers. One of the reasons for this is the high portential for SCC failures of the washers under environmental conditions in service. A broken lockwasher is a very serious condition.
The failure that you mention sounds like inadequate preload on installation. I have NEVER seen a properly tightened and designed A325 joint loosen in service. Lock washers will not prevent a failure due to improper installation.
Dick
RE: Lock washers on A325 bolts?
Hg
Eng-Tips policies: FAQ731-376
RE: Lock washers on A325 bolts?
Revision F of the standard has been in effect since 1996. It states: "Where high-strength bolts are used and tensioned in accordance with AISC "Specification for Structural Joints Using ASTM A325 or A490 Bolts", a nut-locking device is not required"
Revision G, put into effect on January 1, 2006 states: "4.9.2 Nut-Locking Devices - Bolts used to connect load-carrying members shall be provided with a nut locking device or mechanism such as, but not limited to, lock nuts, lock washers, or palnuts, to prevent loosening, except as provided in 4.9.3 (Pre-tensioned bolts)
This tells me that not only are lock washers allowed on this type of structure, they (or other locking device) are required, except for pre-tensioned connections.
Screwman - until two weeks ago, I would have completely agreed with you regarding inadequate preload. I too have never seen such loosening other than on this structure. I have since learned that these particular bolts were tightened 3 times in 5 years and repeatedly kept loosening. I talked to the mechanics who tightened them and they claim that they used 3/4" drive sockets and really "reefed on them". Thanks for your input.
RE: Lock washers on A325 bolts?
If the bolts do not require full tension there should be no problem with a lock washer, but why use one?
RE: Lock washers on A325 bolts?
Hope this helps.
RE: Lock washers on A325 bolts?
Tunalover
RE: Lock washers on A325 bolts?
Although the section wasn't contemplated as such, paragraph 2.6.2 pertaining to 'alternative washer type indicating devices' might be read to recognize lock washers IF they are approved by the EOR. (It would be a stretch to suggest anyone had that in mind when that language was incorporated.)
Perhaps the SAE Fasteners Committee said it best when the following language was written in SAEJ489: "It should be noted that the word 'lock' appearing in the names of the products in this standard is a generic term historicially associated with their identification and is not intended to imply an indefinate permenancy of fixity in attachments where they are used."
Or, as Hollywood would say it, "This story was inspired by a true locking fastener."
Ausgang
SAE/RCSC/ASTM Member
RE: Lock washers on A325 bolts?
I routinely inspect telecommunication towers, which obviously see cyclical wind loads to an extreme degree. Hundreds or thousands of load cycles per day would not be unusual in many cases. Lately I have observed a number of loose bolts which used Anco nuts (these are the nuts with a lock wire that runs through the nut and "catches" on the threads of the bolt).
Although split washers are somewhat less common, I have observed no loose bolts with this type of locking device (nor have I observed any broken washers). I'm wondering what thermal effects may have to do with this phenomenon, as here in New England we see temperature variations greater than 100 degrees F over the course of a year. I've not been able to find anything definitive as yet on that subject.
My question was really on the requirements of AISC, not to reopen the debate on the effectiveness of split washers. Nonetheless, my observations seem counter to the prevailing consensus.
Thanks again.
RE: Lock washers on A325 bolts?
and that the lock washers having less surface area
is allowing you to have greater tension in
the bolts and that is what is helping your
situation. If you are using a tension devise,
then forget this comment.
RE: Lock washers on A325 bolts?
Having built a few towers in my youth and since most of the fasteners were 7/8" or larger in diameter A325 or A490 galvanized exclusively with hardened washers and Anco nuts...the above quote tells me a lot. I recall we used a hydraulic multiplier on the larger bolts and a pleumatic impact wrench that was dutifully calibrated on a Skidmore each morning before we mounted the tower!!! I know it was a long time ago, but...the last tower I worked on was the KNX radio tower in Hawthorn, CA. in 1966...it's still there!
Rod