Lecture -04 Bolted Connections For print

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N-W.F.P. University of Engineering and Technology Peshawar

Lecture 04: Bolted Connections

CE-409: Lecture 04 Prof. Dr. Akhtar Naeem Khan 1

By: Prof Dr. Akhtar Naeem [email protected]

Topics to be AddressedTypes of connectors

Tightening proceduresg g p

Behavior of Bolted & Riveted connections

Types of Bolted connections

Types of connection failures

CE-409: Lecture 04 Prof. Dr Akhtar Naeem Khan 2

Code Requirements

Design Examples

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Components which make up the complete structure are fastened together

Types of Connectors

complete structure are fastened together by means of:

1. RIVETS (older version)2. BOLTS (newer version)


3. WELDS

1. Rivets:They are made from rivet bar stock in a machine which forms one head and shears the

Types of Connectors

rivet to desired length.Steel rivets are always heated before drivingMost rivets are driven by pressure-type riveters which complete riveting in one stroke.


Typical Round Head Rivet

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Rivets are generally made from steel

1. Rivets:

Types of Connectors

Rivets are generally made from steel conforming to ASTM A502 and comes in 2 grades:i. Grade 1(carbon steel)

ii. Grade 2 (carbon-manganese steel)


1. Rivets:

Types of Connectors

CE-409: Lecture 04 Prof. Dr. Akhtar Naeem Khan

Countersunk RivetRound Head Rivet

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1. Rivets:

Types of Connectors


Types of Connectors1. Rivets: Riveting processes


Rivet Heating Oven Rivet Heater

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Types of Connectors1. Rivets: Riveting processes


Earlier Riveting Gun Modern Riveting Gun

In riveted connections magnitude of

Types of Connectors1. Rivets: Characteristics of riveted connections

gclamping is function of length of rivet and magnitude of shrinkage after the head is formed.

Magnitude of slip depends on the extent

CE-409: Lecture 04 Prof. Dr Akhtar Naeem Khan

to which rivet fills the hole.

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Types of Connectors1. Rivets: Causes of rivet obsolescence

Riveting required a crew of 4 to 5 experienced riveters

Bolt installation is less labor intensive

Riveting is time consuming operation requiring preheating driving and finishing


requiring preheating, driving and finishing

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Types of Connectors1. Rivets: Causes of rivet obsolescence

Rivet strength is low compared to high strength bolts

High strength bolts are now economical

Riveting is still used in some industries and


applications such as aircraft industry

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) U fi i h d (A307)

Types of Connectors2. Bolts: Two common types of bolts are:

a) Unfinished (A307)A307 is known by names unfinished, rough, common, ordinary and machine.

They are made of low carbon steel having tensile strength of 60Ksi.


Types of Connections2. Bolts: Two common types of bolts are:

b) High strength bolt (A325,A449,A490).A325 is made of medium carbon steel whose tensile strength decreases with increase in dia.

High strength bolts can be tightened to large tensions


tensions.

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Types of Connections2. Bolts:


Typical High Strength Bolt

Research Council on Structural Connections (RCSC) prescribes four ti ht i d

Tightening procedures

tightening procedures.

1. Turn of the nut method

2. Calibrated-wrench tightening

3 Installation of alternate design bolts


3. Installation of alternate design bolts

4. Direct-tension-indicator tightening

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Torque Wrench17


Positive Tension Shear Bolt


Bolt Installation Procedure 18

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Direct Tension Indicating Washers19


T = Tensile Force onC ti

TT


Connection∆ = Joint Displacement

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In riveted connections magnitude of


In riveted connections magnitude of clamping is function of length of rivet and magnitude of shrinkage after the head is formed.

Magnitude of slip depends on the extent


Magnitude of slip depends on the extent to which rivet fills the hole.

1. Slip-Critical connectionsC f f

Types of Bolted connection

Connection transmits the force by friction produced between the faying surfaces by the clamping action of the bolts.

Slip-critical connections are recommended for joints subjected to stress reversal,


severe stress fluctuation, impact, vibration or where slip is objectionable

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The clamping force applied to the bolt brings the two members close


1. Slip-Critical connections

The clamping force applied to the bolt brings the two members closeenough so that appreciable friction is produced between them whichis then responsible for resisting the load. The more the clampingforce the more is the friction and strong is the connection but theclamping force need not to be greater than tensile strength of thebolt.


Slip critical connection becomes bearing type connection after theslip occurs so every slip critical connection is essentially a bearingtype connection also.

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2. Bearing type connections

Load is transferred by shearing and


y gbearing on the bolt.

Capacity in shear depends on whether shear plane intersects the body of bolt or threaded portion.


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2. Bearing type connections


Bearing type connection is the most widely used general typeconnection in which the load is resisted by the bolt body withoutany friction between faying surfaces.


Type of connection Failures

1 Shearing Failure of Bolts1. Shearing Failure of Bolts.

2. Bearing Failure of plate.

3. Tearing failure at edge of plate.


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1. Shearing failure of bolts



1. Shearing failure of bolts



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2. Bearing Failure of Plate



Shear & Bearing Area



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3. Tearing Failure at edge of Plate



Shearing Failure edge of plate Transverse Tension Failure

Tests showed, failure by tearing through free edge of material will not occur if Le measured parallel to line of applied force is not less diameter of bolt multiplied by ratio of bearing stress

Type of connection Failures3. Tearing Failure at edge of Plate

not less diameter of bolt multiplied by ratio of bearing stress to tensile strength of connected part.


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Force transmitted by the bolt

P f D (A)


P = fp D t ------------------------(A)

Force to cause failure along two shear planes

P = 2(Le – D / 2 ) t τu

τu = 0.7 Fu


P = 1.4DtFu(Le/D –1/2) -----(B)

Equating (A) & (B)

------- (C)


Eqn (C) can be approximated as

So Eqn becomes


So Eqn becomes

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LRFD ASD


φ = 0.75 With FOS= 2

Tearing length or Edge distance


φ 0.75 With FOS 2

LRFD ASD


Spacing between holes


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Eccentricity of Applied Force

Plates of lap joint tends to bend.


Bending produces non uniform bearing of the fastener on the plates


Topic Ref. Text Book Ref. LRFD Code

Code Requirements

Minimum edge Distance Table 2-8 Table J3.4

Allowable Working Stress on Fasteners or Connected Material

Table 2-9

Allowable Load for Slip-Critical Connections

Table 2-10 Table J3.6


Allowable Stresses A502 Rivets

Table 2-12

Design Strength of Fasteners Table 2-13 Table J3.2

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AISC Minimum Edge DistanceCode Requirements


Minimum installation tensionCode Requirements


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Allowable Stresses

Code Requirements


Properties of structural boltsCode Requirements


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Allowable load for Slip critical connectionCode Requirements


Design strength of fastenersCode Requirements


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Design Example No.1 (ASD Method)




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Design Example No.1 (LRFD Method)




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W = 10 int = .25in

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Fub



2”


2”

2”

6”

3”

P = 77 Kips

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Thanks


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Lecture -04 Bolted Connections For print