1. BOLTED CONNECTIONS

2. Teaching Resources for Steel Structures
CONTENTS
Introduction
Bolted Connections
Bolts and Bolting
Force Transfer Mechanism
Failure of Connections
In shear
In tension
Combined shear and tension
Block shear
© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

3. 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

4. Teaching Resources for Steel Structures
TYPES OF CONNECTIONS -!
Classification based on type of force in the bolts
Single
shear
a) Lap Connection
b) Butt Connection
Double shear
Shear Connections
support
(a)
(b)
Tension Connection and Tension plus Shear Connection
© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

5. Teaching Resources for Steel Structures
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
© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

6. FORCE TRANSFER MECHANISM
Bolt Shear Transfer – Free Body Diagram
(a) Bearing Connection
(b) Friction Connection T
Frictional Force T
Clamping Force, PO
Bearing stresses
Tension
in bolt
FORCE TRANSFER MECHANISM

7. Teaching Resources for Steel Structures
TIGHTENING OF HSFG BOLTS
snug-tight
position
¾ turn
Tightening of HSFG bolts
1) Turn-of-nut Tightening
2) Calibrated Wrench Tightening
3) Alternate Design Bolt Installation
4) Direct Tension Indicator Method
(a) Standard
(b) Oversized
(c )Short Slot
(d) Long slot
Feeler gauge
Hole types for HSFG bolts
© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

8. 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
Zone of
plastification
(c) Bearing on Plates
Pbs = pbs d t  ½ e t pbs

9. IS 800:2007 10.3 Bearing Type Bolts lg = 8 d /(3 d+lg)
Shear capacity of bolt
IS 800:2007
Reduction factor in shear for Long Joints
Reduction factor in shear for Large Grip Lengths
lg = 8 d /(3 d+lg)
Reduction factor for Packing Plates
pk = ( tpk)

10. Tb =(0.90 fub An)/ γmb < (fyb Asb (γm1 / γm0))/ γmb
10.3 Bearing Type Bolts
Bearing Capacity of bolt on any ply
Tension Capacity
Bolt subjected to combined shear and tension
Vsb = (2.5 d t fu )/ γmb
Tb =(0.90 fub An)/ γmb < (fyb Asb (γm1 / γm0))/ γmb

11. Vbf = (2.2 d t fup ) / γmf < (3 d t fyp)/ / γmf
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

12. 10.4 Friction Grip Type Bolting
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.

13. TABLE 10.2 TYPICAL AVERAGE VALUES FOR COEFFICIENT OF FRICTION (µf)
Clean mill scale
0.33
Sand blasted surface
0.48
Red lead painted surface
0.1
Treatment of surface
Coefficient of friction (µf)

14. 10.4 Friction Grip Type Bolting
Bearing capacity
Tension capacity
Combined Shear and Tension
Reduction factor in shear for Long Joints will apply here
Vbf = (2.2 d t fup ) / γmf < (3 d t fyp)/ / γmf
Tf = (0.9 fu A)/ / γmf

15. BOLTS UNDER TENSION AND PRYING EFFECT
(b) HSFG
Connection
Bearing type
connection 2T T To
To+T
(d) Prying Effect Q B A b n
T+Q 2T
Proof Load Po
Bolt force
B kN
Applied load 2T (kN)
HSFG
Bearing type
( c) External Tension
versus bolt force

16. 10.4 Friction Grip Type Bolting
Prying Force 
 = 2 for non-pretensioned and 1 for pretensioned
 = 1.5 for LSM
be = effective width of flange per pair of bolts
(Conti….)

17. DESIGN STRENGTHS FOR BOLTED CONNECTIONS
Table 1 Bolt Strengths in Clearance Holes in MPa
Bolt strengths
Bolt grade
4.6
8.8
Shear strength ps
160
375
Bearing strength pbb
435
970
Tension strength pt
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

18. 10.5.9 Stresses due to Individual forces
Combination of stresses
Fillet welds
Combined bearing, bending and shear
(Conti….)

19. 10.2 Fasteners spacing and edge distance
Minimum Spacing times the nominal diameter
Maximum Spacing - shall not exceed 32t or 300 mm, whichever is less, where t is thickness of the thinner plate
pitch shall not exceed 16t or 200 mm, in tension members and 12t or 200 mm, whichever is less, in compression members
Edge and End Distances minimum edge shall be not less than that given in Table maximum edge distance should not exceed 12 t, where  = (250/fy)1/2
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

20. GENERAL ISSUES IN CONNECTION DESIGN
Assumptions in traditional analysis
M = Td
Standard Connections (a) moment
connection (b) simple connection e V T C d
(a)
(b)
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

21. Analysis of Bolt Groups Combined Shear and Moment in-Plane
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

22. Teaching Resources for Steel Structures
TYPES OF CONNECTIONS
Classification based on type of resultant force transferred
(a)
(b)
Concentric Connections
(a)
(b)
Moment Connections
© IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

23. COMBINED SHEAR AND MOMENT IN PLANE P ri
Rmi O x’ y’
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
Rmi=M ri/ ri2
Bolt group eccentrically
loaded in shear
Combined shear

24. COMBINED SHEAR AND MOMENT OUT-OF-PLANETi d li Li NA
d/6
(a)
(b)
(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

25. BEAM AND COLUMN SPLICE Bolted Beam 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

26. 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.

27. BEAM-TO-COLUMN CONNECTIONSV
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 < 0.6d design bolts for shear only
Eliminates need to drill holes in the beam. Limit depth and thickness
t < /2 (Gr.8.8) and /3 (Gr.4.6)

28. 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

29. 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
GussetPlate
Splice
plate e
support
(a) Apex Connection
(b) Support connection
Truss Connections

30. Thank You FATIGUE BEHAVIOUR www.steel-insdag.org
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
Thank You