Bolting Procedures

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



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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



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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



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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



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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



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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.



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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



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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



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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.html


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Direct Tension Indicator Bolts

ASTM F1852-08 Twist-Off Bolts



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Direct Tension Indicator Bolts



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Bolt Installation

Direct Tension Indicators (DTIs)


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Direct Tension Indicator Washers



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Direct Tension Indicator Washers



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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



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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



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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]

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Bolting Procedures