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7/28/2019 Bolting Procedures
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CE470 Lecture 10 Bolts
Types of Fasteners, Properties
Slip-Critical and Bearing-Type
ConnectionsMethods of Tightening Bolts
Tension, Shear, and Bearing capacity of
bolts
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Rivets Mild carbon steel, Fy = 28 38 ksi
Clamping force varied
Bad rivet? Difficult & expensive to remove Required crew of 4 skilled workers
Types of Fasteners
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Types of Fasteners
Unfinished Bolts
Low-carbon steel, ASTM A307, Fu = 60 ksi
Machine, Common bolts Least expensive
Typically used in light structures andsecondary members (small trusses, purlins,girts etc.)
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Types of Fasteners
High-Strength Bolts
started use in 1950s
less bolts required More labor (washers)
Most economical
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Grip is the distance from behind the bolt head to the back of the nut or washer Sum of the thicknesses of all the parts being joined exclusive of washers
Thread length is the threaded portion of the bolt
Bolt length is the distance from behind the bolt head to the end of the bolt
Parts of the Bolt Assembly
HeadShank
Washer
NutWasher
Face
Grip
Thread
Length
Slide courtesy of David Ruby, Ruby & Associates
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WASHERgoes under part youre
using to tighten bolt
(head or nut)
A325
High-Strength Bolts
AISC Table 7-15 [7-80]
Standard dimensions
(F, H, W, thread length)
FH H W
Thread length
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ASTM Material Fub
A325 Mediumcarbon steel
105 - 120 ksi
A490 Heat-treatedalloy steel
150 ksi
Common Sizes
Buildings 3/4 and 7/8
Bridges 7/8 and 1
AISC Table 2-5 [2-41]
for 0.5 to
1 diameter
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Markings
COR
A325
Material Specification
Manufacturer
(initials or abbreviation;
hereCordova Bolt)
Underline if Type 3 bolt
(weathering steel)
Otherwise, Type 1 standard
(Type 2 discontinued)
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SLIP-CRITICAL
Friction-type used when slip resistance desired at service loads
(Joints subject to fatigue, bolts in combination with welds,
anytime deformation due to slip unacceptable for design)
Bolts tightened to
specified tensilestress
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In a slip-critical joint the bolts must be fully pre-tensioned .
This force develops frictional resistance between the connectedelements
The frictional resistance allows the joint to withstand loading without
slipping into bearing, although the bolts must still be designed for
bearing
The slip critical joint faying surfaces may require preparation
Slip-Critical Joints
Slide courtesyof David Ruby,
Ruby &
Associates
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Contact or
bearing onplate
BEARING TYPE
Permitted to be snug-tight all plies in a joint are in firm contact
May be PRE-TENSIONED [AISC J1.10]
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In a bearing joint the connected elements are assumed to slip into bearing
against the body of the bolt
If the joint is designed as a bearing joint, the load is transferred through
bearing whether the bolt is installed snug-tight or pretensioned
Bearing Joints
Slide courtesy of David Ruby, Ruby & Associates
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Bolt InstallationTurn-of-the-nut Simplest method
1/3 to 1/2 turn, typically, beyond snug
tight
Calibrated wrench Manual torque wrenches
Variation +/- 30%
Wrenches MUST be calibrated DAILY
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Turn-of-Nut Method
Slide courtesy of David Ruby, Ruby & Associates
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Turn-of-Nut Method
Installation Procedure:
Check bolts and nuts for rust and lubrication
Install nut and washer with markings up
Washer, if installed, must be under the turned element
Step 1
Tighten bolt to snug tight conditionhaving all faying surfaces in tight contact
Slide courtesy of David Ruby, Ruby & Associates
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Turn-of-Nut Method
Step 3Rotate nut specified
Turn-of-Nut amount
Step 2
Match-Mark bolt tip,
nut and base steel
(this procedure is not requiredBy RCSC specification)
Note: Bolt may be tightened by turning the bolt head
Slide courtesy of David Ruby, Ruby & Associates
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Turn-of-Nut Method
Check for rotated Tolerance
For 1/3 turn, +/- 30 degreesFor 1/2 turn, +/- 30 degrees
For 2/3 turn, +/- 45 degrees
Step 4
Slide courtesy of David Ruby, Ruby & Associates
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Turn-of-Nut Method
The turn-of-nut method of
installation is reliable and
produces bolt pretensions that
are consistently above the
prescribed values.
Slide courtesy of David Ruby, Ruby & Associates
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BoltTension
Turns from Snug
Snug
Proof Load = yield stress x tensile stress area
= approx. 70 80% of tensile capacity
A3257/8 diameter
10K
40K
55K
1/3
to
1/2 3/4 to 1 ~1-3/4
Pretension 39K
= Proof Loadfor A325
Pretension = 70% of tensile capacity
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Calibrated Wrench Method
Slide courtesy of David Ruby, Ruby & Associates
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Calibrated Wrench Method
Skidmore-Wilhelm Calibrator
Portable bolt-tension calibration
-convert tool output to bolt-
tension
-Torque-Control Wrenches
-Conventional Impact Wrenches
-Turn-of-Nut Method
Slide courtesy of David Ruby, Ruby & Associates
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Bolt Installation
Alternative-design bolts
Twist-off or Tension-control bolts
Special wrench required
Spline designed to twist off at requiredlevel of torque / tension
ANIMATION http://www.tcbolts.co.uk/2_installation.html
Spline
http://www.tcbolts.co.uk/2_installation.htmlhttp://www.tcbolts.co.uk/2_installation.html7/28/2019 Bolting Procedures
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Direct Tension Indicator Bolts
ASTM F1852-08 Twist-Off Bolts
Slide courtesy of David Ruby, Ruby & Associates
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Direct Tension Indicator Bolts
Slide courtesy of David Ruby, Ruby & Associates
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Bolt Installation
Direct Tension Indicators (DTIs)
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Direct Tension Indicator Washers
Slide courtesy of David Ruby, Ruby & Associates
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Direct Tension Indicator Washers
Slide courtesy of David Ruby, Ruby & Associates
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TENSION FAILURE SHEAR FAILURE
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BEARING FAILURE
Deformation /
elongation of bolt
hole
Shear rupture /
splitting of plate
B lt d J i t F il M d
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Bolts in bearing joints are designed to meet two limit states:
1. Yielding, which is an inelastic deformation (above left)
2. Fracture, which is a failure of the joint (above left)
The material the bolt bears against is also subject to yielding or fracture
if it is undersized for the load (above right)
Bolted Joint Failure Modes
BearingFracture
Bearing
Yield
Bearing
Yield
BearingFracture
Slide courtesy of David Ruby, Ruby & Associates
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Resistance Factor
un PR
75.0 Use this for :-- tension capacity
-- shear capacity
-- bearing resistance
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bnn AFR
Tensile Strength
butn FFF 75.0
AISC J3.6 [16.1-108],
Table J3.2
Nominal,
unthreaded cross
section (in2)
Tensile stress
capacity
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bbubun AFmAmR )5.0(
Shear Strength bvn AFRAISC J3.6 [16.1-108], Table J3.2
Number of shear
planes
PP
P
P/2 P/2
m = 1
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Shear Strength
P/2
P/2
P
m = 2
P/4P/4
P
P/4P/4
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Shear Strength
b
b
ubun AFmAmR )5.0(
Connection length effect = 0.8shear factor (from tests) = 0.62
0.8 x 0.62 ~ 0.5
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b
b
ubun AFmAmR )4.0(
Shear Strength (threads included)
A325X(threads excluded
from shear plane)
A325N(threads included
in shear plane)
0.5 x 0.75 ~ 0.4
Threads in the Shear Plane
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The shear plane is the
plane between two or
more pieces of steel.
The threads of a HS bolt
may or may not be
assumed to be included in
the shear plane; however,
based on the fixed length
of thread, it is highlyunlikely.
The bolt capacity is
greater with the threads
excluded from the shear
plane
The most commonly used
bolt is an ASTM A325 3/4
HS bolt with the threads
assumed to be included in
the shear plane
Threads in the Shear Plane
Threads Included In The Shear Plane
Threads Excluded From The Shear Plane
Slide courtesy of David Ruby, Ruby & Associates
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Bearing Limit State
Le
t
d
Rn = 2 t [Le- d/2] p
Rn = 3.0Fud tif Le = 2-2/3 d
AISC J3 10 [16 1 111]
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Design Bearing Resistance
uucn dtFtFLR 4.22.1
AISC J3.10 [16.1-111]
Deformation IS a design consideration(do not want hole elongation > inch)
Lc
Lc
Clear distance (in)
AISC J3 10 [16 1 111]
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Design Bearing Resistance
uucn dtFtFLR 4.22.1
AISC J3.10 [16.1-111]
Bolt diameter (in)
Plate / angle thickness (in)
Plate / angle tensile
stress (ksi)
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uucn dtFtFLR 0.35.1
Design Bearing Resistance, contd
)()( individualnboltgroupn RR
Deformation is NOT a design consideration
AISC J3 3 [16 1 106]
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Minimum Spacing
s
bolt
bolt
d
ds
3
3
22
preferred
AISC J3.3 [16.1-106]
AISC T bl J3 4
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Minimum Edge Distances
AISC Table J3.4
Le
BoltDiameter
for ShearedEdge
for RolledEdge
3/4 1-1/4 1
7/8 1-1/2[d] 1-1/8
1 1-3/4[d] 1-1/4
boltd5.1preferred
[d] permitted to be 1-1/4 in. at ends
of beam connection angles and
shear end plates
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AISC J3 5 [16 1 106]
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Maximum Edge Distances
"6
12
e
e
L
tL
AISC J3.5 [16.1-106]