bolted connections bearing

8/8/2019 Bolted Connections Bearing

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1CE321/Dr.DurgeshRai/IITK/2010

Design of Steel Structures

Durgesh C. Rai

Department of Civil Engineering, IIT Kanpur

SteelSteelConnectionsConnections --II

BoltSBoltS


Steel connectionsSteel connections

General

Unlike concrete,connections in steelstructures need specialdesign

Bolts, Rivets and Welds aretypical connectors

CE321/Dr. Durgesh Rai/IITK/2010


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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.


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


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



Bolts in sections

Often more than one bolt used

Fasteners along gauage line

Working point aligned to minimize eccentricity




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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


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


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


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


Typical Bolted Connections

FastenersFasteners



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Typical Bolted Connections

FastenersFasteners


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

20

Table 19, Cl. 10.2.1



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Minimum spacing for fasteners


Cl. 10.2.2 & 10.2.4

20

2.5d

2.5d

1.7do

1.7do

1.4do

1.4do

d

do


Maximum spacing for 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


Bearing failure / Split tension (shear)failure of plate in bearing type connection




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Tension fracture of gusset plate



Block shear failure of gusset plate




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Tension failure of bolt



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



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




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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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



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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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 ]



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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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).



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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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.



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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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 ]



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]

bolted connections bearing

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