Material Ch33&34

8/12/2019 Material Ch33&34

http://slidepdf.com/reader/full/material-ch3334 1/26

Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 1

BOLTED CONNECTIONS

8/12/2019 Material Ch33&34



•

Introduction• Bolted Connections

• Bolts and Bolting

• Force Transfer Mechanism

• Failure of Connections

In shear

In tension

Combined shear and tension

Block shear

CONTENTS

8/12/2019 Material Ch33&34



•

Analysis of Bolt Groups – Combined Shear and Moment in-Plane

– Combined Shear and Moment out-of-plane

• Beam and Column Splices

• Beam to Column Connections

• Beam to Beam Connections

• Truss Connections

• Fatigue Behaviour

CONTENTS -1

8/12/2019 Material Ch33&34



INTRODUCTION

• Designed more conservatively than members because they are more

complex to analyse and discrepancy between analysis and design islarge

• In case of overloading, failure in member is preferred to failure in

connection

• Connections account for more than half the cost of structural steelwork

• Connection design has influence over member design

• Similar to members, connections are also classified as idealised types

Effected through rivets, bolts or weld

• Codal Provisions

8/12/2019 Material Ch33&34



Concentr ic Connect ions

(a) (b)

Moment Connect ions

(a) (b)

TYPES OF CONNECTIONS

Classification based on type of resultant force transferred

8/12/2019 Material Ch33&34



Shear Connect ions

a) Lap Connect ion b) But t Connect ion

support(a)

(b)

Tension Connect ion and Tension plus Shear Conn ect ion

TYPES OF CONNECTIONS -!

Single

shear

Double

shear

Classification based on type of force in the bolts

8/12/2019 Material Ch33&34



BOLTS AND BOLTING

Bolt Grade: Grade 4.6 :- f u = 40 kgf/mm2 and f

y = 0.6*40 = 24 kgf/mm2

Bolt Types: Black, Turned & Fitted, High Strength Friction Grip

Black Bolts:

usually Gr.4.6,

made snug tight,ductile and cheap,

only static loads

Turned & Fitted;

Gr.4.6 to 8.8,

Close tolerance drilled holes,

0.2% proof stressHSFG Bolts:

Gr.8.8 to 10.9,

less ductile,

excellent under dynamic/fatigue loads

8/12/2019 Material Ch33&34



snug-tight

position

¾ turn

position

Tightening of HSFG bolts

Feeler gauge

TIGHTENING OF HSFG BOLTS

1) Turn-of-nut Tightening2) Calibrated Wrench Tightening

3) Alternate Design Bolt Installation

4) Direct Tension Indicator Method

(a) Standard (b) Oversized

(c )Short Slot (d) Long slot

Hole types for HSFG bolts

8/12/2019 Material Ch33&34



Bo lt Shear Transfer – Free Body Diagram

(a) Bear ing Connect ion

(b) Fr ict ion Connect ion

T

Frictional Force T

Clamping Force, PO

Bearing stresses

Tension

in bolt

T

T

T

Clamping Force, PO

FORCE TRANSFER MECHANISM

8/12/2019 Material Ch33&34



(b) HSFG

Connect ion

Bear ing type

connect ion

2T

T T

2T

To To To+ T To+ T

Proof Load

Po

Bol t

force

B kN

Ap pl ied lo ad 2T (kN)

HSFG

Bearing

type

( c) External Tensio n

versus bol t force

BOLTS UNDER TENSION AND PRYING EFFECT

(d) Pryin g Effect

Q Q

B

A

bn

T+Q

2T

T+Q

8/12/2019 Material Ch33&34



PRYING EFFECT AND END PLATE DESIGN

Minimum prying force Q is given by

2

4

272 nb

wt pT

n

bQ o

y

o

p

pt n

The corresponding prying force can then be obtained as Q = M p /n .

If the total force in the bolt (T+Q) exceeds the tensile capacity of the bolt,

then the thickness of the end plate will have to be increased.

QnTb M Qn M B A ; p B A M

Tb M M

2 415.1

2wt p M

y

p

w p

M

t y

p

415.1

min

= 2 (non -prelo aded) = 1.5 for limit state design

w = width/pair of bolts

Po= proof load in consistent units

n is the minimum of end distance or

the minimum thickness of the plate is obtained as follows

8/12/2019 Material Ch33&34



FAILURE OF CONNECTIONS

(a) Shearing of Bolts

(b) Bearing on Bolts

(c) Bearing on Plates

Zone of

plastification

Fig. 9Shear Connections with Bearing Bolts

Ps = ps As where As = 0.8A

Pbb = pbb d t

Pbs = pbs d t ½ e t pbs

8/12/2019 Material Ch33&34



FAILURE OF CONNECTIONS-1

Shear Connections with HSFG Bolts

(a) Slip Resistance

(b) Bearing on Plates

Psl = 1.1 Ks po

Pbg = pbgd t 1/3 e t pbg

Ks =1.0 (clearance hole) = 0.45 (untreated surfaces)

po= proof load

8/12/2019 Material Ch33&34



Bolt strengths Bolt grade

4.6 8.8

Shear strength p s 160 375

Bearing strength p bb

435 970

Tension strength p t 195 450

Steel grade ST42S Gr.43 Gr.50Bearing bolts p

bs 418 460 550

HSFG bolts p bg

650 825 1065

Table 1 Bolt Strengths in Clearance Holes in MPa

Table 2 Bearing Strengths of Connected Parts in MPa

DESIGN STRENGTHS FOR BOLTED CONNECTIONS

8/12/2019 Material Ch33&34



f t /P t

10.4

Shear and Tension

Interact ion Curv e

f s /P s 1

0.4

COMBINED SHEAR AND TENSION

4.1t

t

s

s

P

f

P

f

0.18.0 t

t

sl

sl

P

f

P

f

(a) Bearing Bolts

(a) HSFG Bolts

8/12/2019 Material Ch33&34



Bloc k Shear

BLOCK SHEAR FAILURE

T

A

B C)()( 5.06.0 BC e y ABe y A p A pT

Capacity=Shear Capacity of AB + Tension Capacity of BC

T = (0.62 Avg

f y/M0

+ Atn

f u /M1

)

or

T= (0.62 Avn f u /M1 + Atg f y /M0)

8/12/2019 Material Ch33&34



GENERAL ISSUES IN CONNECTION DESIGN

M = Td

Standard Connections (a) moment

connection (b) simple connection

e

V

T

C

dV

(a) (b)

Assumptions in traditional analysis

• Connection elements are assumed to

be rigid compared to the connectors

• Connector behaviour is assumed to

be linearly elastic

• Distribution of forces arrived at by

assuming idealized load paths

• Provide stiffness according to the

assumed behaviour

• ensure adequate ductility and rotation

capacity

• provide adequate margin of safety

8/12/2019 Material Ch33&34



COMBINED SHEAR AND MOMENT IN PLANE

Bolt group eccentrically

loaded in shear

Pr i

R mi

O

x’

y’

• Bolt shear due to Px

and Py

Rxi = Px /n and Ryi = Py /n

• M = Px y’ + Py x’

• Rmi = k r iMi = k r i

2

MR = k r i2 = k r i2

• Bolt shear due to M

Rmi=M r i / r i2

22

sincos imi yiimi xii R R R R R

2

22

2

22 )()( ii

i y

ii

i xi

y x

Mx

n

P

y x

My

n

P R

Combined shear

8/12/2019 Material Ch33&34



COMBINED SHEAR AND MOMENT OUT-OF-PLANE

Bolt group resisting out-of-plane moment

Ti

d li Li

NAd/6

Li

(a) (b) (c)

C

Ti = kli where k = constant

M = Ti Li = k li Li

Ti = Mli / li Li

Shear assumed to be shared equally and bolts

checked for combined tension+(prying)+shear

8/12/2019 Material Ch33&34



BEAM AND COLUMN SPLICE

Bolted Beam Splice

(a)Conventional

Splice

(b) End-Plate

Splice

Strength, stiffness and ease in erection

Assumptions in

Rolled-section

& Plate Girders

Column Splices – bearing type or HSFG moment splices

8/12/2019 Material Ch33&34



BEAM-TO-COLUMN CONNECTIONS

(a) Simple – transfer only shear at nominal eccentricity

Used in non-sway frames with bracings etc.

Used in frames upto 5 storeys

(b) Semi-rigid – model actual behaviour but make analysis

difficult (linear springs or Adv.Analysis). However lead

to economy in member designs.

(c) Rigid – transfer significant end-moments undergoing

negligible deformations. Used in sway frames for

stability and contribute in resisting lateral loads and

help control sway.

8/12/2019 Material Ch33&34



V


Simple beam-to-column connections a) Clip and seating angle

b) Web cleats c) Curtailed end plate

e

(a) (b) (c)

(a) Economical when automatic saw and drill lines are available

Check end bearing and stiffness of seating angleClip angle used for torsional stability

(b) If depth of cleats < 0.6d design bolts for shear only

(c) Eliminates need to drill holes in the beam. Limit depth and thickness

t < /2 (Gr.8.8) and /3 (Gr.4.6)

8/12/2019 Material Ch33&34




Rigid beam-to-column connections a) Short end plate

b) Extended end plate c) Haunched

columnweb

stiffeners

diagonal

stiffener

web

plate

(a) (b) (c)

8/12/2019 Material Ch33&34



BEAM-TO-BEAM AND

TRUSS CONNECTIONS

(a) Apex Connection

Truss Connections

(b) Support connection

Gusset

Plate

Splice

plate

Gusset

Plate

e

support

Beam-beam connections similar to beam-column connectionsMoment continuity may be obtained between secondary beams

Check for torsion in primary beams

8/12/2019 Material Ch33&34



FATIGUE BEHAVIOUR

Fatigue leads to initiation and growth of cracks under fluctuating stresses

even below the yield stress of the material (High-cycle fatigue)

Fatigue cracks grow from points of stress concentrations

To avoid stress concentrations in bolted connections

• Use gusset plates of proper shape

• Use match drilling

• Use HSFG bolts

Fatigue also depends on range of stress fluctuations and reversal of stress

• pre-tensioned HSFG avoid reversals but lead to fretting corrosion

Fatigue design carried out by means of an S-N curve on a log-log scale

Components are designed below the endurance limit

8/12/2019 Material Ch33&34



Thank You

Documents

Material Ch33&34