Great to have some technical specs for "snug tight". Thanks.
A hammer struck spud wrench? I would think the spec means a typical
tapered spud wrench about 18" long for a 1" bolt. I'd estimate
ironworkers I've met can (easily - no insult intended) apply 80 to 100#
force to a wrench so torques in the 100 to 150 ft-lb range might be a
numerical range for "snug tight". IIRC the ironworkers that erected my
steel building had a 250 ft-lb target for 3/4" A325 bolts, thus I
assume they are "slip critical" joints. (They used a big torque wrench).
The spec cites four conditions to satisfy "snug tight" - 1. the torque
applied, 2. all plies in firm contact, 3. all bolts equally "snug", and
4. a static load. Towers don't satisfy #4 for anchor or leg bolts
since leg tension/compression reverses depending on the direction of the
wind.
Specification for Structural Joints Using High-Strength Bolts, December
31, 2009 RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS 16.2-29 Section
4.1 "Snug-tightened joints are also permitted for statically loaded
applications involving ASTM A325 bolts and ASTM F1852 twist-off-type
tension-control bolt assemblies in direct tension. However,
snug-tightened installation is not permitted for these fasteners in
applications involving non static loading."
hmmm.. perhaps UST compensates by having 4x 1" bolts in each leg for my
HDX589. It seems quite unlikely to me that these bolts ever fail in
shear, which is what holds a snug tight connection together. However,
long term cycling might cause other failure modes.
I did inspect both of my towers for condition #2, "all plies in
contact" Tower 1 passed visual inspection for all bolts having plies in
firm contact. Tower 2 has the opening leg flanges in contact and for
the pivot leg flanges, only 2 of 4 bolts achieve "plies in firm
contact" The gap is about 0.030 to 0.050 between plies (flanges) for
the other 2 bolts. That is with all bolts torqued to 140 ft-lbs and
three full cycles of tightening on each flange. I noticed when
installing the towers, that the fabrication tolerances are such that it
took a lot of bolt torque to achieve any contact on some flanges. I
opted for enough torque to achieve reasonable contact as my working
definition of snug tight.
YMMV,
Grant KZ1W
On 6/25/2013 1:12 PM, KM5VI wrote:
Very well put Mickey and I agree with your 90% comment as well.
Page 51 of the Research Council on Structural Connections (RCSC)
Specification for Structural Joints Using High-Strength Bolts gives us a
technical definition for snug tight:
http://www.boltcouncil.org/files/2009RCSCSpecification.pdf
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Mickey Baker
Sent: Tuesday, June 25, 2013 2:38 PM
To: KM5VI
Cc:towertalk@contesting.com
Subject: Re: [TowerTalk] FW: UST bolt Torque question
There are actually technical definitions for this. As you might imagine,
engineering structures like towers, buildings and bridges, engineers need to
effectively communicate to laborers how they'd like things tightened.
Here's an interesting technical treatise from a fastener manufacturer's
point of view that defines "snug tight" as:
*Snug Tight = The tightness that is required to bring the plies into firm
contact (Typically obtained with a few impacts of an impact wrench or the
full effort of an Iron-worker using an ordinary spud wrench).
*
The original doc can be found at:
http://www.selfdrillers.com/brochures/TDS012-Turn-of-Nut%20Installations.pdf
Dollars to donuts that the average iron worker will normally tighten a nut
tighter than 90% of hams. Ironworkers put the world together - and sometimes
take it apart!
73,
Mickey N4MB
On Tue, Jun 25, 2013 at 3:27 PM, KM5VI<km5vi@flukey.cc> wrote:
Snug tight is a standard term commonly used in the design of bolted
connections that are not slip-critical. Slip-critical connections
rely on the friction created by the clamping action of the threaded
connection and require a minimum fastener torque or bolt stretch
specification to achieve the design friction value. Bolted connection
design based on the simple shear and/or bearing strength of the
fastener do not rely on joint friction, and thus the assembly torque
is non-critical provided that it is tight enough to eliminate slop in
the joint that might over time from load cycles (bolt loosening).
FYI - I have found a spud wrench useful for snug tight connections on
my crank-up tower base connections - it is a short wrench that is
designed to be struck with a hammer.
Hope this helps.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Jim Thomson
Sent: Tuesday, June 25, 2013 7:39 AM
To:towertalk@contesting.com
Subject: [TowerTalk] UST bolt Torque question
I asked UST how much Torque should be used on both the 12 x 1.125
inch anchor rods....and also the 18 x 1 inch leg bolts.
I also told em I used never seize on both anchor rods and legs bolts.
Also told em the anchor rods are 104 ksi yield strength..and came from
portland bolt...and are 60 inchs long each.... with 6 inch threads
on each end. Told em that the 18 x leg bolts are
A325 bolts and are 3 inchs long each. Everything has heavy duty flat
washers and slightly oversized nuts on em.
Their reply was...... snug fit ! This is for my UST HDX-689 tower.
This
is the old style 689..that weighs 5000 lbs..without the ants and mast,
but that
weight includes the bearings and small PP rotor. The crane operator
weighed the tower when it was unloaded.
What is ..snug fit ? Trying to get answers from UST at times can be
exasperating.
Does anybody even know ? I was thinking perhaps 125 ft lbs for the
anchor rods......and 100 ft lbs for the leg bolts. Leg bolts can always
be
replaced...
anchor rods cant.
Tnx... Jim VE7RF
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--
Mickey Baker, N4MB
Fort Lauderdale, FL
*"Tell me, and I will listen. Show me, and I will understand. Involve me,
and I will learn." *Teton Lakota, American Indian Saying.
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