Bolted Connections Bearing
Transcript of Bolted Connections Bearing
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Design of Steel Structures
Durgesh C. Rai
Department of Civil Engineering, IIT Kanpur
SteelSteelConnectionsConnections --II
BoltSBoltS
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Steel connectionsSteel connections
General
Unlike concrete,connections in steelstructures need specialdesign
Bolts, Rivets and Welds aretypical connectors
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Steel connectionsSteel connections
General
Many configurations areused for force transfer inconnections.
Configuration dependsupon the type of
connecting elements,
nature and magnitude ofthe forces (and moments),
available equipment,fabrication and
erection considerations,cost, etc.
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Limited bolting possible
ProblemsProblems
Skewed shear connection
Pipe-column base connection
Column-baseconnection
Field-bolted moment
connection
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Elements involvedElements involved
Pure bolting
May not be possible in large steel structures
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Limited bolting possible
Small widths of flanges and depths of webs
ConnectionsConnections
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Bolts in sections
Sometimes simple to use
Reduce sectional area
Disturb smooth flowof forces
Particularly atcritical sections
Elements involvedElements involved
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Bolts in sections
Often more than one bolt used
Fasteners along gauage line
Working point aligned to minimize eccentricity
Elements involvedElements involved
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Two types
Rivets
Bolts
RivetRivet High StrengthHexagonal Head Bolt
High StrengthHexagonal Head Bolt
High StrengthInterference Body Bolt
High StrengthInterference Body Bolt
FastenersFasteners
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Rivets Old style connectors Permanent, Need field heating and head forming Safety issues Load distribution is not as good as that for bolts
Initial prestress Due to heating and cooling in riveting procedureTension on cooling is not estimated accurately
FastenersFasteners
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Rivets Installation process
Heat rivet Insert in hole Hammer to produce the second
head Cool and expands to form a
tight joint
Seldom used nowadays Labour intensive & noisy
operation Less expensive alternatives
FastenersFasteners
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Bolts
FastenersFasteners
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Two sub-types of High Strength Bolts
Bearing Type
Snug-tight bolts Provide enough tension so that the surfaces are in contact and
firmly bear on each other
Joint may slip Load is resisted by shear and bearing
Usually employed in gravity load applicationsWhen slip is not critical
FastenersFasteners
Snug tightSnug tight
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Two sub-types of High Strength Bolts
Friction Type (Slip-Critical)
Pre-torque the bolts with torque wrench Bolts are usually subjected to large tensile forces (~0.7fy)
Joint slips only when critical shear is exceeded Resists loads through friction without slip
Usually employed in applications of cyclic,repetitive, fatigue and dynamic loading
Good for seismic applications
CalledHigh Strength Friction Grip
(HSFG) Bolts
FastenersFasteners
Pre-torquePre-torque
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High Strength Bolts
Specifications for manufacture
IS:3757
Specifications for design
IS:4000
FastenersFasteners
Thread Nut Shank Head
Thread Length
Nominal Bolt Length
Thread Nut Shank Head
Thread Length
Nominal Bolt Length
Heavy-hex structural bolt and heavy-hex nut
ThreadLength
BoltLength
1.65 D 0.8D
D
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Typical Bolted Connections
FastenersFasteners
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Typical Bolted Connections
FastenersFasteners
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Clearance for holes for fasteners
Bolt slips in the holes under cyclic loading
Problem more serious when slotted holes are used
Bolt holes for 20 mm diameter boltsBolt holes for 20 mm diameter bolts
Location Details of FastenersLocation Details of Fasteners
22 26 28 50
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Table 19, Cl. 10.2.1
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Minimum spacing for fasteners
Location Details of FastenersLocation Details of Fasteners
Cl. 10.2.2 & 10.2.4
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2.5d
2.5d
1.7do
1.7do
1.4do
1.4do
d
do
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Maximum spacing for fasteners
Location Details of FastenersLocation Details of Fasteners
Cl. 10.2.2 & 10.2.4
1.4do
d
do
32tor 300 mm
16tor 200 mm for tension12tor 200 mm in comp.
12t16tor 200 mm
4t+ 40 mm
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Shear transfer in bearing type connection
Bearing typeBearing type
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Bearing failure / Split tension (shear)failure of plate in bearing type connection
Bearing typeBearing type
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Tension fracture of gusset plate
Bearing typeBearing type
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Block shear failure of gusset plate
Bearing typeBearing type
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Tension failure of bolt
Bearing typeBearing type
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Failure modes of bolted connections
FastenersFasteners
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Shear Load transfer in bearing type connection
Shank and plate in bearing
Shank in single shear
Bearing typeBearing type
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Load transfer in bearing type connection
Bearing failure of shank/plate; tearing failure of plate
Threads in double shear
Bearing Type boltsBearing Type bolts
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Shear transfer in bearing type connection
Bearing typeBearing type
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Bearing typeBearing type
Design of bearing type connection
sb dbV V
min( ; )db dsb dpbV V V=
Factoredshear force
Design shearstrength of bolt
Limit state of shear
Designstrength of bolt
Design bearing strength
of bolt on any plate
Limit state of bearing
[ Cl. 10.3.2 ]
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Bearing typeBearing type
Limit State of Shear inbearing type connection
; 1.25dsb nsb mb mbV V =
( )3u
nsb n nb s sb lj lg pk
fV n A n A = +
Shear planesin threads
Shear planesin shank
2( 4)( 0.9328 )nbA d p= Area at root of threads,
d = Dia. of bolt in mmp = Pitch of threads in mmAliter:If threads are intercepted,reduce bolt area to 70%
[ Cl. 10.3.3 ]
Reduction Factors
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Bearing typeBearing type
Limit State of Shear in bearing type connection
( )3u
nsb n nb s sb lj lg pk
fV n A n A = +
Reduction factor for long jointswhen joint length exceeds 15 d
1.075 0.005( ); 0.075 1.0lj j ljl d =
Not applied when shear distribution isuniform, e.g., connection of web to flange
[ Cl. 10.3.3.1 ]
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Bearing typeBearing type
Limit State of Shear in bearing type connection
( )3u
nsb n nb s sb lj lg pkg
fV n A n A = +
Reduction factor for long gripswhen joint grip exceeds 5 dbut restricted to max. of 8 d
8/(3 )lg g ljl d = +
As grip length increases, bolts are
subjected to greater bendingmoments in addition to shearforces
[ Cl. 10.3.3.2 ]
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Bearing typeBearing type
Limit state of Shear in bearing type connection
( )3
ubnsb n nb s sb lj lg pk
fV n A n A = +
Reduction factor for packing plates (shims)when shims are thicker than 6 mm
1 0.0125 ;pk pk pkt t in mm =
Usually provided to match dimensions
[ Cl. 10.3.3.3 ]
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Bearing typeBearing type
Limit State of Bearing in bearing type connection
23u
n
FV e t=
Tear-out at the edge or betweentwo holes in direction of thebearing load
To prevent excessiveelongation of bolt holes, theload is limited to bearingarea times fracture stress
n uV C F d t=
Vn
0.5 Vn0.5 Vn
t e
t
d
C = 2.4 for limiting holedeformation to 6 mm (RCSC 2004).
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Bearing typeBearing type
Limit State of Bearingin bearing type connection
1.2 2.4n u uV F e t F d t=
(2.5 )npb b u hV k d t f =
IS 800 Approach
d = dia. of bolt
do = dia. of hole
e = end dist. along bearing dir.
p = pitch distance
fub = UTS of bolt
fu = UTS of plate
0 0
min [ , 0.25, , 1.0]3 3
ubb
u
p fek
d d f=
[ Cl. 10.3.4 ]
1.0
0.7 &
0.5h
STD
OVS SSL
LSL
=
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Bearing typeBearing type
Example in bearing type connection
40 60 830min[ 0.25 1.0]
3(22) 3(22) 410
min[0.6 0.66 2.0 1.0] 0.6
bk =
= =
(2.5 )npb b u hV k d t f =
d = 20 mm, do = 22 mm
e = 40 mm, p = 60 mm
fub = 830 MPa, fu = 410 MPa
[ Cl. 10.2.4.2]
Calculate the strength of the bolts in the lap splice inFigure. M20 Grade 8.8 bolts in 22mm clearance holesand E250 (Fe 410) plate.
Solution
Bolts are in single shear in standard holes.
Shear capacity per bolt
Bearing capacity of thinner plate per bolt
The full value is appropriate since the end distance
( )3
ubnsb n nb s sb lj lg pk
fV n A n A = +
2830 [0 1 (20 ) ] 15043
nsb
MPaV mm kN
= + =
2.5 0.6 20 16 410 197npbV mm mm MPa kN = =0 0
min [ 0.25 1.0]
3 3
ubb
u
p fek
d d f
=
( 40 ) 1.7 ( 37.4 )oe mm d mm= =
Nominal joint capacity in tension as governed by bolt strength = 3150 = 450 kN.
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Bearing typeBearing type
Limit State of Tensionin bearing type connection
Rupture Strengthon net bolt areaat bottom ofthreads w/opartial safetyfactor
b dbT T
; 1.25db nb mb mbT T = =
min [0.90 ; ]mbnb ub n yb sbmo
T f A f A
=
Yield strength onshank areaincreasedbypartial safetyfactor for bolts
[ Cl. 10.3.5]
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Bearing typeBearing type
Block Shear in bearing type connection
1
1
0.9
3min
0.9
3
vg y tn u
mmo
dbtg yvn u
mom
A f f
TfA f
+
=
+
[ Cl. 6.4 ]
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Bearing typeBearing type
Combined Shear and Tension in bearing type connection
Ratio of factoredshear forcedemand toDesign shear
strength
2 2
1.0sb b
db db
V T
V T
+
Ratio of factoredtensile forcedemand toDesign tensilestrength
[ Cl. 10.3.6]
[ Cl. 10.3.5][ Cl. 10.3.2]