lecture -04 bolted connections

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

Peshawar

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

By: Prof Dr. Akhtar Naeem [email protected]

Lecture 04: Bolted Connections

CE-409: Lecture 04 Prof. Dr Akhtar Naeem Khan 3

Topics to be AddressedTypes of connectors

Tightening procedures

Behavior of Bolted & Riveted connections

Types of Bolted connections

Types of connection failures

Code Requirements

Design Examples


Components which make up the complete structure are fastened together by means of:

1. RIVETS (older version)

2. BOLTS (newer version)

3. WELDS

Types of Connectors


1. Rivets: They are made from rivet bar stock in a

machine which forms one head and shears the rivet to desired length.

Steel rivets are always heated before driving

Most rivets are driven by pressure-type riveters which complete riveting in one stroke.

Types of Connectors

Typical Round Head Rivet

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

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

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

Countersunk RivetRound Head Rivet

1. Rivets:

Types of Connectors

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1. Rivets:

Types of Connectors

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Rivet Heating Oven Rivet Heater

Types of Connectors1. Rivets: Riveting processes


Earlier Riveting Gun Modern Riveting Gun

Types of Connectors1. Rivets: Riveting processes


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 to which rivet fills the hole.

Types of Connectors1. Rivets: Characteristics of riveted connections

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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

Types of Connectors1. Rivets: Causes of rivet obsolescence

( Structural Non Usage Rivets )

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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

Types of Connectors1. Rivets: Causes of rivet obsolescence

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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 Connectors2. 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.

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


Types of Connections2. Bolts:

Typical High Strength Bolt


Research Council on Structural Connections (RCSC) prescribes four tightening procedures.

1.Turn of the nut method

2.Calibrated-wrench tightening

3.Installation of alternate design bolts

4.Direct-tension-indicator tightening



Torque Wrench


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Positive Tension Shear Bolt

Bolt Installation Procedure


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Direct Tension Indicating Washers


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T = Tensile Force on

Connection

∆ = Joint Displacement

TT


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T = Tensile Force on

Connection

∆ = Joint Displacement

TT


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1. Slip-Critical connections

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

Types of Bolted connection

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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 the clamping force need not to be greater than tensile strength of thebolt.


1. Slip-Critical connections

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

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2. Bearing type connections

Load is transferred by shearing and bearing 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 type connection in which the load is resisted by the bolt body without any friction between faying surfaces.

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Type of connection Failures

1. Shearing Failure of Bolts.

2. Bearing Failure of plate.

3. Tearing failure at edge of plate.


1. Shearing failure of bolts



2. Bearing Failure of Plate



Shear & Bearing Area



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 to tensile strength of connected part.

Type of connection Failures3. Tearing Failure at edge of Plate


Force transmitted by the bolt

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

Force to cause failure along two shear planes

P = 2(Le – D / 2 ) t u

u = 0.7 Fu

P = 1.4DtFu(Le/D –1/2) -----(B)

Equating (A) & (B)



------- (C)

Eqn (C) can be approximated as

So Eqn becomes



LRFD ASD

= 0.75 With FOS= 2

Tearing length or Edge distance



LRFD ASD


Spacing between holes


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

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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Code Requirements


AISC Minimum Edge Distance

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Code Requirements


Minimum installation tension

Code Requirements


Allowable Stresses

Code Requirements


Properties of structural bolts

Code Requirements


Allowable load for Slip critical connection

Code Requirements


Design strength of fasteners

Code Requirements


Design Example No.1 (ASD Method)

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Design Example No.1 (LRFD Method)


W = 10 int = .25in

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Fub

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2”

2”

2”

6”

3”

P = 77 Kips

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Thanks

lecture -04 bolted connections

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