Transcript Document

BOLTED CONNECTIONS
Dr S R Satish Kumar, IIT Madras
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CONTENTS
• Introduction
• Bolted Connections
• Bolts and Bolting
• Force Transfer Mechanism
• Failure of Connections
In shear
In tension
Combined shear and tension
Block shear
Dr S R Satish Kumar, IIT Madras
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INTRODUCTION
• Designed more conservatively than members because they are more
complex to analyse and discrepancy between analysis and design is
large
• In case of overloading, failure in member is preferred to failure in
connection
• Connections account for more than half the cost of structural steel
work
• 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
Dr S R Satish Kumar, IIT Madras
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TYPES OF CONNECTIONS -!
Classification based on type of force in the bolts
Single
shear
Double
shear
a) Lap Connection
b) Butt Connection
Shear Connections
support
(a)
(b)
Tension Connection and Tension plus Shear Connection
Dr S R Satish Kumar, IIT Madras
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BOLTS AND BOLTING
Bolt Grade: Grade 4.6 :- fu = 40 kgf/mm2 and fy = 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 stress
HSFG Bolts:
Gr.8.8 to 10.9,
less ductile,
excellent under dynamic/fatigue loads
Dr S R Satish Kumar, IIT Madras
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FORCE TRANSFER MECHANISM
(a) Bearing Connection
T
Bearing stresses
T
(b) Friction Connection
T
Tension
in bolt
Frictional Force T
Clamping Force, PO
T
Clamping Force, PO
Bolt Shear Transfer – Free Body Diagram
Dr S R Satish Kumar, IIT Madras
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TIGHTENING OF HSFG BOLTS
1) Turn-of-nut Tightening
2) Calibrated Wrench Tightening
3) Alternate Design Bolt Installation
4) Direct Tension Indicator Method
¾ turn
position
snug-tight
position
Tightening of HSFG bolts
(a) Standard
(b) Oversized
(c )Short Slot
(d) Long slot
Feeler gauge
Hole types for HSFG bolts
Dr S R Satish Kumar, IIT Madras
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FAILURE OF CONNECTIONS
Shear Connections with Bearing Bolts
Fig. 9
(a) Shearing of Bolts
Ps = ps As where As = 0.8A
(b) Bearing on Bolts
Pbb = pbb d t
(c) Bearing on Plates
Zone of
plastification
Pbs = pbs d t  ½ e t pbs
Dr S R Satish Kumar, IIT Madras
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10.3 Bearing Type Bolts
10.3.2 Shear capacity of bolt
fu
nn Anb  ns Asb  / mb
Vsb 
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10.3.1.1 Reduction factor in shear for Long Joints
βlj  1.075 - (l j /200d)
but 0.75  βlj  1.0
10.3.1.2 Reduction factor in shear for Large Grip Lengths
lg = 8 d /(3 d+lg)
10.3.2.3 Reduction factor for Packing Plates
pk = (1 - 0.0125 tpk)
Dr S R Satish Kumar, IIT Madras
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10.3 Bearing Type Bolts
10.3.3 Bearing Capacity of bolt on any ply
Vsb = (2.5 d t fu )/ γmb
10.3.4 Tension Capacity
Tb =(0.90 fub An)/ γmb
10.3.5
< (fyb Asb (γm1 / γm0))/ γmb
Bolt subjected to combined shear and tension
 V

V
 sd
2
2
  T 
   e   1.0
 T 
  nd 
Dr S R Satish Kumar, IIT Madras
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FAILURE OF CONNECTIONS-1
Shear Connections with HSFG Bolts
(a) Slip Resistance
Vsf = (µf ne Kh Fo)/ γmf
Kh =1.0 (clearance hole)
 = 0.45 (untreated surfaces)
Fo= proof load
(b) Bearing on Plates
Vbf = (2.2 d t fup ) / γmf < (3 d t fyp)/ / γmf
Dr S R Satish Kumar, IIT Madras
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10.4
Friction Grip Type Bolting
10.4.1 Slip resistance
Vsf = (µf ne Kh Fo)/ γmf
Where,
µf = coeff. of friction (slip factor) as in Table 10.2 (µf < 0.55)
ne = number of effective interfaces offering frictional resistance to slip
Kh = 1.0 for fasteners in clearance holes
= 0.85 for fasteners in oversized and short slotted holes
= 0.7 for fasteners in long slotted holes loaded parallel to the slot.
γmf = 1.10 (if slip resistance is designed at service load)
γmf = 1.25 (if slip resistance is designed at ultimate load)
Fo = minimum bolt tension (proof load) at installation ( 0.8 Asb fo)
Asb = shank area of the bolt
fo = proof stress (= 0.70 fub)
Note: Vns may be evaluated at a service load or ultimate load using
appropriate partial safety factors, depending upon whether slip resistance
is required at service load or ultimate load.
Dr S R Satish Kumar, IIT Madras
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TABLE 10.2 TYPICAL AVERAGE VALUES FOR
COEFFICIENT OF FRICTION (µf)
Treatment of surface
Coefficient
of friction
(µf)
Clean mill scale
0.33
Sand blasted surface
0.48
Red lead painted surface
0.1
Dr S R Satish Kumar, IIT Madras
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10.4
Friction Grip Type Bolting
10.4.2 Bearing capacity
Vbf = (2.2 d t fup ) / γmf < (3 d t fyp)/ / γmf
10.4.3 Tension capacity
Tf = (0.9 fu A)/ / γmf
10.4.4 Combined Shear and Tension
Reduction factor in shear for Long Joints will apply here
Dr S R Satish Kumar, IIT Madras
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BOLTS UNDER TENSION AND PRYING EFFECT
2T
Bearing type
connection
T
2T
(b) HSFG
Connection
To
T
To
To+T
To+T
2T
Bolt
force
B kN
HSFG
B b
Bearing
type
Proof Load
Po
Applied load 2T (kN)
( c) External Tension
versus bolt force
Dr S R Satish Kumar, IIT Madras
n
A
Q
Q
T+Q
T+Q
(d) Prying Effect
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10.4
Friction Grip Type Bolting
10.4.5 Prying Force
4



f
b
t
l 
o e 
v
Q
T 


2
e
2l
27 l l

e
e
v


 = 2 for non-pretensioned and 1 for pretensioned
 = 1.5 for LSM
be = effective width of flange per pair of bolts
Dr S R Satish Kumar, IIT Madras
(Conti….)
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DESIGN STRENGTHS FOR BOLTED CONNECTIONS
Table 1 Bolt Strengths in Clearance Holes in MPa
Bolt strengths
Shear strength ps
Bearing strength pbb
Tension strength pt
Bolt grade
4.6
8.8
160
375
435
970
195
450
Table 2 Bearing Strengths of Connected Parts in MPa
Steel grade
ST42S
Gr.43
Gr.50
Bearing bolts pbs
418
460
550
HSFG bolts pbg
650
825
1065
Dr S R Satish Kumar, IIT Madras
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10.5.9 Stresses due to Individual forces
fa
P
or q =
t t lw
10.5.10 Combination of stresses
10.5.10.1 Fillet welds
fe 
f a2  3q 2 
fu
3  mw
Combined bearing, bending and shear
2
2
f = f +f
+ f f + 3q 2
e
b
br
b br
Dr S R Satish Kumar, IIT Madras
(Conti….)
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10.2 Fasteners spacing and edge distance
10.2.1 Minimum Spacing - 2.5 times the nominal diameter
10.2.2 Maximum Spacing - shall not exceed 32t or 300 mm,
whichever is less, where t is thickness of the thinner plate
10.2.2.2 pitch shall not exceed 16t or 200 mm, in tension members
and 12t or 200 mm, whichever is less, in compression members
10.2.3 Edge and End Distances minimum edge shall be not less
than that given in Table 10.1. maximum edge distance should not
exceed 12 t, where  = (250/fy)1/2
10.2.4 Tacking Fasteners spacing in line not exceeding 32t or 300
mm If exposed to the weather, 16 t or 200 mm
max. spacing in tension members 1000 mm
max. spacing in compression members 600 mm
Dr S R Satish Kumar, IIT Madras
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GENERAL ISSUES IN CONNECTION DESIGN
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
Dr S R Satish Kumar, IIT Madras
T
V
d
C
V
e
M = Td
(a)
(b)
Standard Connections (a) moment
connection (b) simple connection
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CONTENTS -1
• 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
Dr S R Satish Kumar, IIT Madras
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TYPES OF CONNECTIONS
Classification based on type of resultant force transferred
(a)
(b)
Concentric Connections
(a)
(b)
Moment Connections
Dr S R Satish Kumar, IIT Madras
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COMBINED SHEAR AND MOMENT IN PLANE
• Bolt shear due to Px and Py
Rxi = Px/n and Ryi = Py/n
ri
• M = Px y’ + Py x’
• Rmi = k ri
Mi = k ri2
MR =  k ri2 = k  ri2
• Bolt shear due to M
Rmi=M ri/ ri2
Combined shear
Ri 
R
xi
x’
Rmi

P
y’
O
Bolt group eccentrically
loaded in shear
 Rmi cos i 2  R yi  Rmi sin  i 2

2
2
 P




P
My
Mx
 x

y
i
i
Ri   






2
2
2
2
n
(
x

y
)
n
(
x

y
)
 i i    i i  


Dr S R Satish Kumar, IIT Madras
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COMBINED SHEAR AND MOMENT OUT-OF-PLANE
Ti
d li
d/6
(a)
Li
NA
(b)
Li
C
(c)
Bolt group resisting out-of-plane moment
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
Dr S R Satish Kumar, IIT Madras
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BEAM AND COLUMN SPLICE
Strength, stiffness and ease in erection
Assumptions in
Rolled-section
& Plate Girders
(a)Conventional
Splice
(b) End-Plate
Splice
Bolted Beam Splice
Column Splices – bearing type or HSFG moment splices
Dr S R Satish Kumar, IIT Madras
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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.
Dr S R Satish Kumar, IIT Madras
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BEAM-TO-COLUMN CONNECTIONS
(a)
e
V
(b)
(c)
Simple beam-to-column connections a) Clip and seating angle
b) Web cleats c) Curtailed end plate
(a) Economical when automatic saw and drill lines are available
Check end bearing and stiffness of seating angle
Clip 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)
Dr S R Satish Kumar, IIT Madras
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BEAM-TO-COLUMN CONNECTIONS
column
web
stiffeners
(a)
diagonal
stiffener
(b)
web
plate
(c)
Rigid beam-to-column connections a) Short end plate
b) Extended end plate c) Haunched
Dr S R Satish Kumar, IIT Madras
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BEAM-TO-BEAM AND
TRUSS CONNECTIONS
Beam-beam connections similar to beam-column connections
Moment continuity may be obtained between secondary beams
Check for torsion in primary beams
Splice
plate
Gusset
Plate
Gusset
Plate
(a) Apex Connection
e
support
(b) Support connection
Truss Connections
Dr S R Satish Kumar, IIT Madras
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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
www.steel-insdag.org
Thank You
Dr S R Satish Kumar, IIT Madras
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