HomeMy WebLinkAboutSPECIAL INSPECTION STEEL - 18-00424 - 940 N 2nd E - Christensen Body Shop16.2-29
static loading, nor for applications I it"Volving ASTM A490 halts and ASITNI'
r?28O gist uit-pe xensit�-cont of Dolt assernll(s
4.2. Pretensioned Joints
Pretensioned joints are required in the following applications:
(1) Joints in which fastener pretension is required in the specification or code
that invokes this Specification;
(2) Joints that are subject to significant load reversal;
(3) Joints that are subject to fatigue load with no reversal of the loading
direction;
(4) Joints with ASTM A325 or F1852 bolts that are subject to tensile fatigue;
and,
(5) Joints with ASTM A490 or F2280 bolts that are subject to tension or
combined shear and tension, with or without fatigue.
Bolts in pretensioned joints subject to shear shall be designed in
accordance with the applicable provisions of Sections 5.1 and 5.3, installed in
accordance with Section 8.2 and inspected in accordance with Section 9.2. Bolts
in pretensioned joints subject to tension or combined shear and tension shall be
designed in accordance with the applicable provisions of Sections 5.1, 5.2, 5.3
and 5.5, installed in accordance with Section 8.2 and inspected in accordance
with Section 9.2. As indicated in Section 4 and Table 4.1, requirements for
faying surface condition shall not apply to pretensioned joints.
Camrnentidr}�;. ,.
Under tileprovisj"ons of some other.specification,. certain shear connections are
requircd to be pretensioned, but are riot required to be slip -critical: Several cases
are kiven for example, in RISC "Speeifieation Section �J1 10 (A1SC . 20 t 0:)-
wherein certain bolted joittts'in bearing connections are to be pretensioned
regardless of whether or riot the potential- for- slip is a concern.. The AISC~
Specification .. requires that joints be preteitsioncd 'nn the following
Circ mstances
(1) Column splices in building; with high ratios of height to width;
(2) Conttct:tions of members that proxide bracing, to columns in tall buildings;
(3) arious:conrreca rms in, building' with Cranes over 5_toii_capacity, ,and,
(4) C ctnhc f ttbn , fttr supports sof ruttnitig machinery and other sources of.itnpact
or stress reversal_
When preteilsion is desired,for reasons other than the necessity to prevent slip;
apt tear �iorte l joi,at +ltoulcl be specified"ip,i,be:conitact,documents.
Speeijieation for• StrticturaiJointy Usingltigh-Strength Botts, December 31. 2009
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-59
SECTION 9. INSPECTION
When inspection is required in the contract documents, the inspector shall ensure while
the work is in progress that the requirements in this Specification are met. When
inspection is not required in the contract documents, the contractor shall ensure while
the work is in progress that the requirements in this Specification are met.
For joints that are designated in the contract documents as snug -tightened joints,
the inspection shall be in accordance with Section 9.1. For joints that are designated in
the contract documents as pretensioned, the inspection shall be in accordance with
Section 9.2. For joints that are designated in the contract documents as slip -critical, the
inspection shall be in accordance with Section 9.3.
9.1. Snug -Tightened Joints
Prior to the start of work, it shall be ensured that all fastener components to be
used in the work meet the requirements in Section 2. Subsequently, it shall be
ensured that all connected plies meet the requirements in Section 3.1 and all bolt
holes meet the requirements in Sections 3.3 and 3.4. After the connections
have been assembled, it shall be visually ensured that the plies of the connected
elements have been brought into firm contact and that washers have been used
as required in Section 6. It shall be determined that all of the bolts in the joint
have been tightened sufficiently to prevent the turning of the nuts without the
use of a wrench. No further evidence of conformity is required for snug -
tightened joints. Where visual inspection indicates that the fastener may not
have been sufficiently tightened to prevent the removal of the nut by hand, the
inspector shall physically check for this condition for the fastener.
�'`ommentary:.
Inspection, requirements for tened joints consist of verification that the
proper fastener components were used, the connected elements were fabricated
properly; the bolted joint was drawn into firm contact, and that the nits could
nit be removed without the use of a wrench liec arse pretension, beyond what
is required to ensure that the nut cannot be removed fruit the bolt without the
use of a wrench; i:: not required for the proper petfdrtnance of a Vlag. titghteiwd
joint, the installed,bolts should not be inspected.to determine the actual installed
pretension, Likewise, the arbitration procedures described in Section 10 are not
�applic:ablc.
9.2. Pretensioned Joints
For pretensioned joints, the following inspection shall be performed in addition
to that required in Section 9.1:
(1) When the turn -of -nut pretensioning method is used for installation, the
inspection shall be in accordance with Section 9.2.1;
Specification for Structural Joints UsingHigh-Strength Bollc. December 31, 2009
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-60
(2) When the calibrated wrench pretensioning method is used for installation,
the inspection shall be in accordance with Section 9.2.2;
(3) When the twist -off -type tension -control bolt pretensioning method is used
for installation, the inspection shall be in accordance with Section 9.2.3;
(4) When the direct -tension -indicator pretensioning method is used for
installation, the inspection shall be in accordance with Section 9.2.4; and,
(5) When alternative -design fasteners that meet the requirements of Section 2.8
or alternative washer -type indicating devices that meet the requirements of
Section 2.6.2 are used, the inspection shall be in accordance with inspection
instructions provided by the manufacturer and approved by the Engineer of
Record.
When ointy are designated as pretensroi c d, 1130y are not subject to the saris V
faying-surface-treatinept inspection requirefil eats as is specified for slit)-ca'iti(I;a
Joints in SectionJ: .
'turn -of -Nut Pretensionittg- The inspector shall observe the pre -installation
verification testing required in Section 8.2.1. Subsequently, it shall be ensured
by routine observation that the bolting crew properly rotates the turned element
relative to the unturned element by the amount specified in Table 8.2.
Alternatively, when fastener assemblies are match -marked after the initial fit -
up of the, joint but prior to pretensioning, visual inspection after pretensioning is
permitted in lieu of routine observation. No further evidence of conformity is
required. A pretension that is greater- than the value specified in Table 8.1 shall
not be cause for rejection.
Nlateh-inarking of tliiassembly during; installation as disetrssed in the
C ommentat-; to Section Sa 1 improve the ability to inspect bolts that have been
pretensioned with the turn -of ntitpretensioning iarethod. 'Thc sides. of:nuts and
bolt licads that have been iinpaeted sufficiently to induce the. Table 4:1
minitn ini pretensibn,will_appear slightly,peened,-
The. 'turn=bf nut _pretonsibiiing method, when properly applied and
verified dwing the constiuction, provides_ more reliable installer pretensions-
than after -the -fact rizsixotion testing. Therefore, proper 41ss �c ction of the method
is for the ihspectot to observe dtt regttired pre -installation verification tesiingof
the fi�slener us.Y<a»icltc,v. unci. the method to be used, foll6wed by monitoring of
the Fork in progress to ensure that the method is routine]), and properly applied,
,or visual, inspection of matc=h-ima ke.d assemblies.
Soiue. probletns Witt' the tutu of -tint pretensioning rrrethodhave been
cAvoumcr&J -Mth hot -dip galvanized bolts. In sorne cases. the pro I blems hive
been attributed to an especially etie-rtitFe tul-)ricarit applied by I the
ttrMA(favairorw, vuswv that bolts acid hats from stoctc will meet the,ASTM
STM
Specification for Structural Joints UsingHigh-Strength Bolts, December 31, 2009
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-61
Specification requirements for mininium turns IcSting of galvanized fasteners,
x:19 site testing ill tale tt"Ision cahbratordernonstYated that the lr bricatit reduced:
the coefficient of friction between the holt and nut to the degree that "tile ftdt
efforr of ;tri ironworker using an ordinary spud wrench" to snug -tighten the joint
actual(v, induced the full required pretension, Also, because the nuts could be
removed with an ordinary spud trench they Avere,erroneousty judged by the
Inspector to be improperly pretensioned, Excessively hibricated; hilt str tt lr�
a *ts way, require significantly less torque to ind ice tlie_. specified reten icyna_
The required pre -installation verification will reveal this potential problem.C:onve2seiy, the absence of lubrication or lack,of proper aver -zapping
can cause seizing of the nut and bolt threads, w=hich will t'csult in a twist failure
oftize bolt at lessthan the .specified pretetnion. Fol, such situ ariorI , the (Ise of a
tclnsion calibrator to check the bolt assembliz s to be installed will be ficip i] in
establis1hing the.need,for lubrication:
9.2.2. Calibrated Wrench Pretensioning: The inspector shall observe the pre-
installation verification testing required in Section 8.2.2. Subsequently, it shall
be ensured by routine observation that the bolting crew properly applies the
calibrated wrench to the turned element. No further evidence of conformity is
required. A pretension that is greater than the value specified in Table 8.1 shall
not be cause for rejection.
For proper inspection of the: method. it 11 is ne cessary, for the inspnc° or to obseivc
the required pre -installation verification testing of the, fpst acr assen1;b ;c=_s and
the method to be used, followed- by monitoring of the work in progress to =tiuslue
that the method is routiaely and properly applied within the ;limits oft tin4
betweeirremoval final pretcnsioltittg.
9.2.3. Twist -Off -Type Tension -Control Bolt Pretensioning: The inspector shall
observe the pre -installation verification testing required in Section 8.2.3.
Subsequently, it shall be ensured by routine observation that the splined ends
are properly severed during installation by the bolting crew. No further evidence
of conformity is required. A pretension that is greater than the value specified in
Table 8.1 shall not be cause for rejection.
6w: Iuuen'tal7 "
The sheare&off splined end of an installed twist -off -type tension -
control bolt
assembly riterely :signifies that at some. time the bolt was ,ilbjcctc&to a tort{ue
that was adequate: to cause the shearing. It in fact all fasteners are
individually prctelisiened in a single continuous o0cration without first, properly
Snug -tightening' all fasteners, they ,inay give a n isleading indication that they
boli have been `properly retensioued. Therefore. it is necessary that the-
rtrs cctar observe the required preinstallati n .exit cation testing of th _{ a r nu,
Specification Ja- Structural Joints Using High -Strength Botts, December 31. 2009
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
16.2-62
cassoinhlies,. and the ability to apply partial tension piior tri twist -off is:
demonstrated. This is foliow ed by monitoring of the work in progress to ensure;,
that the method is routinely and properly applied within the, limits On time"
between removal groin prate, cled storage and final It',vist-city of the spline end. '
9.2.4. Direct -Tension -Indicator Pretensioning: The inspector shall observe the pre-
installation verification testing required in Section 8.2.4. Subsequently, but
prior to pretensioning, it shall be ensured by routine obsernation that the
appropriate feeler gage is accepted in at least half of the spaces between the
protrusions of the direct tension indicator and that the protrusions are properly
oriented away from the work. If the appropriate feeler gage is accepted in fewer
than half of the spaces, the direct tension indicator shall be removed and
replaced. After pretensioning, it shall be ensured by routine observation that the
appropriate feeler gage is refused entry into at least half of the spaces between
the protrusions. No further evidence of conformity is required. A pretension that
is greater than that specified in Table 8.1 shall not be cause for rejection.
1 ocrttnentu y: _
When theJoint is initially snug ziOwned', the diTeCt tension indicator arch -like
protrusions will generally cornpress partial1v Whenever the snug-ti4htenin��'
t atiou causes one-half or iron ga
e#' the ps 'between these :etch -like
protrusions co close to 0.015 in. or less (o.()G_5 III. or less for coated direct
1e1 Ision indicators), the direct tension indicator'should be jeplaeed. Only atter
this initial operatixin should the bolts be pretensioned in a systematic manner. If
the bolts are installed and pretensioned in a single continuous opetatian, :direct
tension indicators :may give'the"inspectur.a misleading indication that thebolts
have been prolvrly,pretensioned. Therefore, it is necessary that the inspector
observe the required ' pre -installation verification testing of the ftas ener-
usseinblles with the .cdireet-tension indicators properl} located and the ntethod to
he used, f +flowing this operation, the inspector slioul& tiionitor the work III
progress to ensure:that the, method is; routinely and properly applied.
9.3. Slip -Critical Joints
Prior to assembly, it shall be visually verified that the.faying surfaces of slip -
critical joints meet the requirements in Section 3.2.2. Subsequently, the
inspection required in Section 9.2 shall be performed.
Caiirdruc>rtt0 y;
When l ,iras are specified its slip -critical, it is necessary to verify that the f ving
stafitcc Condition meet;; the, requirements as specified in the contract documents
prior to a:,scinbly of tho oint and that the Dolts
are properly pretensioned ager
they, have been installed, Accordingly, tlt.( inspcetioti requirementfor slip-,
critical joints are identical to those specified in Section 9.2. with additional
JAYing,rslujave condition inspection rcquircm-,nts..
Specification for Structural Joints UsingHigh-Strength BoILC, December 31, 2009
RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS
Turn-of-Nut/Part Turn Method
Turn -of -glut
Note: As with every bolt pretensioning method, Turn -of -Nut may only be
performed after all steel plies in a connection have been drawn into firm
contact, i.e. snug -tightened. Failure to do so will result in inadequate bolt
pretension and loose connections. Also, The Pre -installation Verification
fastener testing must be conducted per applicable RCSC sections with the
caveat that Turn -of -Nut verification may not verified by Direct Tension
Indicator verification (RCSC 48).
Turn -of -Nut is performed by rotating the nut or bolt of a fastener assembly
a specific turn angle based on the fastener's length, and diameter while
restraining the unturned element from rotating.
Pre -installation Verification
Per AISC/RCSC section 7 preinstallation verification, fastener assembly testing must be
conducted, onsite, by the installation crew, using actual installation tools. Contrary to popular
opinion Preinstallation Verification testing DOES NOT pass or fail fastener assemblies. Testing
is intended to discover possible issues between fasteners, tools and installers, before field
bolting operations commence.
The next few sections describe instances that may be highlighted by preinstallation testing
results. Note, while this document references the RCSC specification section 7, both tension
tables (tables 7.1 & 8.1) in the RCSC specification are incorrect for A325 diameters 1-1/8" and
above. Therefore, AISC 360-16 table J3.1 will be referenced instead.
Fasteners
Are the fastener assemblies capable of achieving 105%, or more, of minimum required bolt
tension at all?
Torque must be applied to the fastener assembly until the tension calibrator indicates adequate
tension or the bolt fails, whichever occurs first. Failure occurs by either the bolt breaking before
minimum tension, or tensile load climbs and then falls, as indicated by the tension calibrator,
without ever achieving minimum tension. Except for TC bolts', applying additional lubricant may
alleviate failure. However, if additional lubricant solves bolt failure, all fasteners represented by
lubricated test samples, must be similarly lubricated.
I AISC 348-14, the Research Council on Structural Connections, Suecification for Structural joints Usine H'Lyh
Strength Bolts: Section 2.2 "ASTM F1852 and F2280 twist -off -type tension -control bolt assemblies and alternative -
design fasteners that meet the requirements in Section 2.8 shall not be relubricated, except by the manufacturer."
Tools
Do the installation tools have enough output torque to tighten adequately lubricated fastener
assemblies, to at least 105% of minimum required tension?
If the full effort of an installation tool applied to a fastener assembly, does not result in at least
105% of required minimum tension, the tool must be replaced for testing as well as for
installation. While not always true, an adequate installation tool should have a drive chuck at
least as large as the fasteners being tightened. For example; when tightening 3/" bolts, the
installation tool should have a square drive chuck of 3/4" or more. Also, a tool's manual may
claim a higher output torque than the tool can produce. Such claims are usually stated vaguely,
such as, claiming the tool's motor can produce some high amount of torque. This statement
may describe no-load torque output but once load is applied, the high torque described will not
be realized.
Installation crews
Do the installers understand how to employ the selected method?
The installers must understand that a snugged tightened condition must be achieved before the
tensioning method is employed. Once a snugcondition exists,
the installers must fully
understand the method they employ and not confuse, or combine, fundamentals of individual
methods. Such as applying a torque value to rotate the nut to turn angle listed for Turn of Nut or
employing a torque wrench as an inspection technique after the turn is complete. Doing so
combines elements of Calibrated Wrench and Turn of Nut.
Snug -tightened Joints
Every bolted joint must be snug -tightened before a pre -tensioning method can be performed.
Snug -tighten is defined as the effort applied to bring the steel plies into firm contact. AISC/
RCSC describes the effort as the full effort of an ironworker or a few impacts of an impact
wrench (8.1) until the nut cannot removed by hand. An attempt at manual nut removal is the
only requirement for inspection (9.1). There is no pretension requirement for a "snugged" joint.
Per AISC's S cificatiQn &Z S��! i% (360-16) Section J3:
"There are no specific minimum or maximum tension requirements for snug -tight bolts."
The snug -tight condition is critical for the Turn of Nut method since it relies on the snug position
as its starting point. With only hand tight as the inspection criteria, Snug -tight may begin with a
pretension that is negligible or zero. If so, the turn listed in table 8.2 may result in less than
minimum required pretension to comply with AISC 360-16 Table J3.1.
Conversely, snug -tightening may result in a pretension near or greater than the minimum
required, and the required turn may strip or break the bolt when employed. This is especially
true of bolt diameters 3/4" and below.
E
Snug -tightening does not affect the success of other methods. Calibrated wrench, DTIs, and TC
bolts do not use a snug position a starting point. If aggressive (high snugging) occurs, these
methods will alert those involved aggressive snugging has occurred. A DTI will flatten, a TC bolt
will shear, or a calibrated wrench will not advance the nut/bolt during the pretensioning
operation. If low snugging occurs, the same three methods will work as designed. The DTI and
TC bolt will remain intact and a Calibrated Wrench will continue to tighten until the stall torque is
reached.
Pre -installation Verification Basics
The following content applies to AISC/RCSC Pre -installation testing only. Individual projects,
State DOTS and Federal Highway specifications may differ substantially and will not be covered
here. The following represents Applied Bolting Technology's interpretation of AISC/RCSC
preinstallation testing based on AISC 348-14 and AISC 360-16. Anyone interested in a different
interpretation is welcome to read the documents themselves.
Verification testing can be summarized as snug tightening, at least three sample fastener
assemblies, in or with, a tension calibrator, applying the selected pre -tensioning method, and
confirming at least 105% of minimum required tension has been achieved. While each method
accomplishes this with different tools, fastener components, or tightening techniques, all 4
tensioning methods follow these basic principles of snug fastener, apply method, and verify
conformity to specification. Lastly, all acceptable methods are expected to permanently deform
the fastener into its inelastic region2.
Sampling
Pre -installation verification testing begins with sampling. Per AISC/RCSC section 7.2:
"A representative sample of not fewer than three complete fastener assemblies of each
combination of diameter, length, grade and lot to be used in the work shall be checked at
the site of installation in a tension calibrator to verify that the pretensioning method
develops a pretension that is equal to or greater than that specified in Table 7.13." SEE
FOOTNOTE4
Regardless of method, it is critical that assembly samples be TRULY REPRESENTATIVE, that
is, in similar condition as fasteners being actively pretensioned. Testing a "new" fastener,
removed directly from sealed shipping receptacles, does not constitute a representative sample,
unless only new condition fasteners are actively being pretensioned.
_................ ........ _.......
...........
2 RCSC 16.2-42 "In any of the foregoing installation methods, it can be expected that a portion of the bolt assembly
(the threaded portion of the bolt within the grip length and/or the engaged threads of the nut and bolt) will reach
the inelastic region of behavior. This permanent distortion has no undesirable effect on the subsequent
performance of the bolt."
3 RCSC Table 7.1 is incorrect, use AISC 360-16 J3.1.
4 Refer to AISC 360-16 Table J3.1, Minimum Bolt Pretension, kips
Fasteners that have been snug tightened & exposed to the weather, for any amount time, must
be verified as is, if this condition accurately represents the fasteners' being tightened in the
steelwork. TRULY REPRESENTATIVE samples are especially important for TC bolts and
Calibrated Wrench installation and testing because these methods are negatively affected by
weathering and lubrication degradation.
Tension Calibrator Steps
1. Place each unique configuration of sample fastener assembly in a tension calibrator with
washers positioned in accordance with table 6.1, if necessary, and 6. 2.
2. Snug the fastener in accordance with AISC/RCSC section 8.1 and inspect per 9.1.
3. Apply the appropriate turn angle based on the ratio of the bolt diameter to its length
(table 8.2).
4. Verify the resulting pre -tension meets or exceeds 105% of the minimum required bolt
pre -tension of the value listed in AISC 360-16 table J3.1.
5. If the turn angle does not produce adequate tension per table J3.1, continue turning until
the resulting pre -tension meets or exceeds 105% of the minimum required bolt pre-
tension as listed in table J3.1. Since table 8.2 permits an upper tolerance for each
rotation angle/turn, it is allowable to rotate the nut beyond the value listed in the table.
However, if more turn is necessary, the ACTUAL turn angle/rotation determined must be
used for field bolting operations, and not the table's listed turn.
Bolting Methodology:
1. Determine the ratio between the fastener's length and diameter as well as the slope
disposition of the outer steel plies.
2. Snug the steel plies, in as many steps as necessary, to bring the steel into firm contact
as required by RCSC 8.1.
3. Using a marker, or similar, draw a mark from the center of the end of the bolt, across the
nut, and onto the steel. This will indicate the starting position of the nut.
4. Apply the specified turn from the appropriate table, or from tension calibrator testing,
while the unturned element is restrained from rotation (usually requiring a second
installer).
5. Rotation exceeding the table can be ignored and may not be corrected or reworked
except by replacing the fastener assembly.
Figure 2: Marked nut, bolt & steel, before and after 213 turn.
For reference, values from table 8.2 of the Research Council on Structural
Connection's (RCSC) Specification for Structural Joints using Nigh Strength Bolts, 2014,
on the next page.
Nut Rotation from Snug -Tight Condition Table
Flat Surfaces One face normal to bolt
Balt Length under Bolt Head axis, other sloped not
and Nut more than 1:20
s 4D
4D:s 8D
BD:s 12D
1/3 turn
1/2 turn
2/3 turn
1/2 turn
2/3 turn
5/6 turn
Both faces sloped not
more than 1:20 from
normal to bolt axis
2/3 turn
:ES/6turn
1 turn
Nut rotation is relative to bolt regardless of the element (nut or bolt) being turned. For all required nut rotations, the tolerance is
plus 60 degrees (6 turn) and minus 30 degrees.
Applicable only to joints in which all material within the grip is steel.
When the bolt length exceeds 12db, the required nut rotation shall be determined by actual testing in a suitable tension calibrator
that simulates the conditions of solidly fitting steel.
Beveled washer not used.
Inspection
The inspector MUST:
1. Verify pre -installation verification has been performed.
2. Verify the joint has been snug -tightened.
3. Verify the original position of all elements.
4. Routinely witness the installation crew turning the nuts/bolts.
5. Verify the final rotated position of all elements.
6. Prohibit excessive rotation discovered or witnessed from being adjusted to reflect turn
values from table 8.2.
5
The inspector MUST NOT.
1. Use a torque wrench as an inspection tool. Inspection is only as described above,
verifying initial position at snug and final position after nut is turned.
2. Assume marking was applied prior to turning. Tightening and THEN marking the nut,
after the turn is a very popular way to perform Turn -of -Nut and is an undetectable
deception, if initial position marks are not observed by the inspector.
3. Instruct bolting crews to back off any turn that is greater than what appears in the table.
Over rotation is not a cause for rejection or rework. Compensating for over rotation, by
backing the nut off, will result in less than the required pretension.
While it is recommended that the bolt, nut, and steel be marked and inspected prior to Turn -of -
Nut implementation, this step is not mandatory. In any case, failure to inspect nuts in their
original (snug), un -turned position will result in unverifiable Turn -of -Nut execution. Nut marking
does not relieve an inspector's responsibility to inspect the connection twice, before and after
the turn.
Minimum Bolt Tension Per AISC 360-16, Table 13.1
t„G rrornrnurn wrisiie srrengm of bolts as specified in ASTM F3125IF3125M for grades A325 and
A490 bolts, with UNC threads, rounded to the nearest kip.
0
Advisories:
Ineffective for some bolts, The Guide:
Users of large diameter high-strength bolts, especially A490 bolts, should be aware that the
RCSC specification requirement for installation of short grip bolts may not produce the required
preload [pretension]. If such bolts are to be used in a slip -resistant joint [i.e., slip critical and pre-
tensioned], calibration tests in a load -indicating device are advisable. (Kulak 59)
Hot Dipped Galvanizing, RCSC:
Some problems with the turn -of -nut pretensioning method have been encountered with hot -dip
galvanized bolts. (RCSC 60).
Bolt Lubrication too effective or absent, RCSC:
Specification requirements for minimum turns testing of galvanized fasteners. Job -site testing in
the tension calibrator demonstrated that the lubricant reduced the coefficient of friction between
the bolt and nut to the degree that "the full effort of an ironworker using an ordinary spud
wrench" to snug -tighten the joint actually induced the full required pretension. Also, because the
nuts could be removed with an ordinary spud wrench, they were erroneously judged by the
inspector to be improperly pretensioned. Excessively lubricated high-strength bolts may require
significantly less torque to induce the specified pretension. The required pre -installation
verification will reveal this potential problem.
Conversely, the absence of lubrication or lack of proper over -tapping can cause seizing of the
nut and bolt threads, which will result in a twist failure of the bolt at less than the specified
pretension. (RCSC 61).
RCSC section 9.1 snug -tightened inspection criteria flawed:
RCSC section 9.2.1 requires the inspector to witness one element being rotated relative to the
other. If not, improper tension may result if an installation crew only applies the minimum
amount of snug -tightening per section 9.1, Snug Tightened Joints:
9.1 ...It shall be determined that all of the bolts in the joint have been tightened
sufficiently to prevent the turning of the nuts without the use of a wrench. No further
evidence of conformity is required for snug -tightened joints.
If only hand tightening is used as a snug inspection criterion, it is possible for Turn -of -Nut's initial
starting point, (i.e. adequate snug) will not be achieved and the method will fail. Such failures
will not depend on whether fasteners were marked or not.
Canadian Institute of Steel
Construction (CIBC) Turn -of -Nut
Installation:
VA
The CISC Turn -of -Nut installation method is similar to AISC/RCSC Turn -of -Nut with a few
exceptions.
1. Required turn values are the same when both faces normal as well as when one face is
sloped 1:20.
2. 3/4 turn to be applied to all instances, when both faces sloped 1:20.
3. The acceptable rotation tolerance is ±300.
4. Beveled washers are required when either steel ply is sloped 1:20 Max when using
ASTM A490 and A490M bolts.
5. CISC Turn Table 8 does not limit itself to 12" maximum bolt length, as the RCSC does.
6. When both surfaces sloped 1:20 max, all bolts rotated 3/4 turn (RCSC requires length
dependent turn values).
For a complete turn details, please refer to the Nut Rotation from Snug -Tight Condition table
within the latest CISC Handbook of Steel Construction.
Inspection:
The inspector MUST -
1 -
UST:
1. Verify pre -installation verification of all assemblies has been performed.
2. Verify the joint has been snug -tightened.
3. Verify the original position of all elements.
4. Verify the final rotated position of all elements.
5. Routinely witness the installation crew actually turning the nuts/bolts.
6. Prohibit excessive rotation discovered or witnessed from being adjusted to reflect turn
values from the applicable table within the CISC handbook.
While it is recommended that the bolt, nut, and steel be marked and inspected prior to Turn -of -
Nut implementation, this step is not mandatory. In any case, failure to inspect nuts in their
original (snug), un -turned position will result in unverifiable Turn -of -Nut execution. Nut marking
does not relieve an inspector's responsibility to inspect the connection twice, before and after
the turn.
0
a .<<• ,t+� u, rnurxrng recnnique clearly indicating 1::3rd tarn, However, the t{gree bolts an the lett
are ready for initlai inspection, the three on the right appear turned but it is impossible to know if
they were turned or marked to appear turned.
CISC Advisories:
See advisories for AISC & RCSC.
Additional Advisories:
While the CISC does not specifically require Pre -installation Verification testing of all fasteners
when using Turn -of -Nut per se, testing is recommended to assure hardware compliance with the
appropriate ASTM Specification. Thread failure (stripping) will not be discernible otherwise.
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-- ---" --" - 'I -WO I MU UAULE angle Is not obvious since the lines
extend completely through the bolts'diameters. Nevertheless, without inspection of their initial position, turn Or
whether the joint was properly snug -tightened, induced pretension cannot be verified.
Figure 3: Obvious deception attempt. while markings suggest each nut or bolt has been rotated, the nut
10