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Transcript of Material Ch33&34
8/12/2019 Material Ch33&34
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 1
BOLTED CONNECTIONS
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 2
•
Introduction• Bolted Connections
• Bolts and Bolting
• Force Transfer Mechanism
• Failure of Connections
In shear
In tension
Combined shear and tension
Block shear
CONTENTS
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 3
•
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
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 4
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
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 5
Concentr ic Connect ions
(a) (b)
Moment Connect ions
(a) (b)
TYPES OF CONNECTIONS
Classification based on type of resultant force transferred
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 6
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
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 7
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
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Teaching Resources © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta 8
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
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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
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(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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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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.
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V
BEAM-TO-COLUMN CONNECTIONS
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)
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BEAM-TO-COLUMN CONNECTIONS
Rigid beam-to-column connections a) Short end plate
b) Extended end plate c) Haunched
columnweb
stiffeners
diagonal
stiffener
web
plate
(a) (b) (c)
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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
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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
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Thank You