BOLTED CONNECTIONS

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BOLTED CONNECTIONS
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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

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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

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TYPES OF CONNECTIONS -!
Classification based on type of force in the bolts
Single shear
Double shear
Shear Connections
Tension Connection and Tension plus Shear
Connection
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BOLTS AND BOLTING
Bolt Grade Grade 4.6 - fu 40 kgf/mm2 and fy
0.640 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
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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
Hole types for HSFG bolts
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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
Pbs pbs d t ? ½ e t pbs
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10.3 Bearing Type Bolts

• 10.3.2 Shear capacity of bolt

IS 8002007
10.3.1.1 Reduction factor in shear for Long
Joints
10.3.1.2 Reduction factor in shear for Large
Grip Lengths
?lg 8 d /(3 dlg)
10.3.2.3 Reduction factor for Packing Plates
?pk (1 - 0.0125 tpk)
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10.3 Bearing Type Bolts

• 10.3.3 Bearing Capacity of bolt on any ply
• 10.3.4 Tension Capacity
• 10.3.5 Bolt subjected to combined shear and
  tension

Vsb (2.5 d t fu )/ ?mb
Tb (0.90 fub An)/ ?mb lt (fyb Asb (?m1 /
?m0))/ ?mb
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FAILURE OF CONNECTIONS-1
Shear Connections with HSFG Bolts
(a) Slip Resistance
Vsf (µf ne Kh Fo)/ ?mf
Kh 1.0 (clearance hole) ? 0.45 (untreated
surfaces) Fo proof load
(b) Bearing on Plates
Vbf (2.2 d t fup ) / ?mf lt (3 d t fyp)/ / ?mf
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10.4 Friction Grip Type Bolting

• 10.4.1 Slip resistance

Vsf (µf ne Kh Fo)/ ?mf
Where, µf coeff. of friction (slip factor) as
in Table 10.2 (µf lt 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. ?mf 1.10 (if slip
resistance is designed at service load) ?mf
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.
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TABLE 10.2 TYPICAL AVERAGE VALUES FOR COEFFICIENT
OF FRICTION (µf)
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10.4 Friction Grip Type Bolting
10.4.2 Bearing capacity 10.4.3 Tension
capacity 10.4.4 Combined Shear and
Tension Reduction factor in shear for Long
Joints will apply here
Vbf (2.2 d t fup ) / ?mf lt (3 d t fyp)/ / ?mf
Tf (0.9 fu A)/ / ?mf
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BOLTS UNDER TENSION AND PRYING EFFECT
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10.4 Friction Grip Type Bolting

• 10.4.5 Prying Force

?
? 2 for non-pretensioned and 1 for
pretensioned ? 1.5 for LSM be effective width
of flange per pair of bolts
(Conti.)
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DESIGN STRENGTHS FOR BOLTED CONNECTIONS
Table 1 Bolt Strengths in Clearance Holes in MPa
Table 2 Bearing Strengths of Connected Parts in
MPa
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• 10.5.9 Stresses due to Individual forces
• 10.5.10 Combination of stresses
• 10.5.10.1 Fillet welds
• Combined bearing, bending and shear

(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

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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

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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

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TYPES OF CONNECTIONS
Classification based on type of resultant force
transferred
Concentric Connections
Moment Connections
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COMBINED SHEAR AND MOMENT IN PLANE

• Bolt shear due to Px and Py
• Rxi Px/n and Ryi Py/n

• M Px y Py x

• Rmi k ri
• Mi k ri2
• MR ? k ri2 k ? ri2

• Bolt shear due to M
• RmiM ri/? ri2

Bolt group eccentrically loaded in shear
Combined shear
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COMBINED SHEAR AND MOMENT OUT-OF-PLANE
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
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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
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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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BEAM-TO-COLUMN CONNECTIONS
e
(a)
(b)
(c)
V
Simple beam-to-column connections a) Clip
and seating angle b) Web cleats c)
Curtailed end plate

• Economical when automatic saw and drill lines are
  available
• Check end bearing and stiffness of seating
  angle
• Clip angle used for torsional stability
• If depth of cleats lt 0.6d design bolts for shear
  only
• Eliminates need to drill holes in the beam. Limit
  depth and thickness
• t lt ?/2 (Gr.8.8) and ?/3 (Gr.4.6)

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BEAM-TO-COLUMN CONNECTIONS
column web stiffeners
diagonal stiffener
web plate
(a)
(b)
(c)
Rigid beam-to-column connections a) Short end
plate b) Extended end plate c) Haunched
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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
(a) Apex Connection
(b) Support connection
Truss Connections
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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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