TYPES OF JOINTS

•WELDED JOINTS

– Fillet welding

– Butt welding

•BOLTED JOINTS

– Bearing type Carbon steel / High strength

– Friction type HSFG

•RIVETED JOINTS

– Mild steel

– High strength steel

1

BOLTED JOINTS Bearing Type:

2

Clamping

Force, P0

Contact

Pressure, P0

T

Frictional

Force T

T

T

XBearing

Stress

Notice slip in bearing

type of connection

Dr S R

Satish

Kumar

, IIT

3

Bolt Shear Transfer – Free Body Diagram

(a) Bearing

Connection

(b) Friction

Connection

T

Frictional Force

TClamping Force,

PO

Bearing stresses

Tension

in bolt

T

T

T

Clamping Force,

PO

FORCE TRANSFER MECHANISM

BOLTED JOINTS Bearing Type:

4

Clamping

Force, P0

T

T

XBearing

Stress

Contact

Pressure, P0

T

T

Frictional

Force T

Notice no slip is observed in-

between plates in HSFG

Connection

Friction Type:

MERITSWelded Joints

– Transfer of forces between elements more direct

– Requires little additional elements like gussets

–Shorter length of joints

– No reduction in member strength due to bolt holes etc.

– Rigid connections easy to achieve

5

DEMERITS

Requires skilled manpower

Requires special equipment

not easy to achieve at difficult locations

less ductile

prone to defects & fatigue cracks under cyclic loading

6

MERITS & DEMERITSBolted Connections

Bearing Type

– Easy to install even at difficult locations

– Economical

– Does not require highly skilled manpower

– Slip causes flexible joint

– Joint size larger

7

BOLTED JOINTS

8

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

9

• 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 Provisions10

Concentric

Connections

(a) (b)

Moment

Connections

(a) (b)

TYPES OF JOINTS

Classification based on type of resultant force transferred

11

Shear Connections

a) Lap

Connection

b) Butt

Connection

support(a)

(b)

Tension Connection and Tension plus Shear Connection

TYPES OF JOINTS -!

Single

shear

Double

shear

Classification based on type of force in the bolts

12

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 loads13

snug-tight

position

¾ turn

position

Tightening of HSFG bolts

Feeler

gauge

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

Hole types for HSFG bolts

14

Bolt Shear Transfer – Free Body Diagram

(a) Bearing Connection

(b) Friction

Connection

T

Frictional Force

TClamping Force,

PO

Bearing stresses

Tension

in bolt

T

T

T

Clamping Force, PO

FORCE TRANSFER MECHANISM

15

(b) HSFG

Connection

Bearing type

connection

2

T

T T

2

T

T

o

T

o

To+

T

To+

T

Proof Load

Po

Bolt force

B kN

Applied load 2T

(kN)

HSFG

Bearing

type

( c) External Tension

versus bolt force

BOLTS UNDER TENSION AND PRYING EFFECT

(d) Prying Effect

Q Q

B

A

bn

T+Q

2T

T+Q16

BOLTED STEEL JOINTS

Bolts in tension

Bolts in shear

6 x 200 =1200 kN

FAILURE MODES OF BOLTS IN SHEAR

Hole tearout

Bolt shear

Hole bearing

FAILURE OF CONNECTIONS

(a) Shearing of Bolts

(b) Bearing on Bolts

(c) Tension capacityZone of

plastificat

ion

Shear Connections with Bearing Bolts

Tnb = 0.90 fub An < fyb Asb (γmb / γm0)

3

sbsnbnu

nsb AnAnf

V

Vnpb = 2.5 kb d t f’u

19

20

(b) HSFG

Connection

Bearing

type

connection

2

T

T T

2

T

T

o

T

o

To+

T

To+

T

Proof Load

Po

Bolt

force

B kN

Applied load 2T

(kN)

HSFG

Bearin

g type

( c) External

Tension

versus bolt

force

BOLTS UNDER TENSION AND PRYING EFFECT

(d) Prying Effect

Q Q

B

A

bn

T+

Q

2

T

T+

Q

FAILURE OF CONNECTIONS

Shear Connections with HSFG Bolts

(a) Slip Resistance

(b) Bearing on Plates

Vnsf = µf. ne. Kh. Fo

Pbg = pbgd t 1/3 e t pbg

Kh =1.0 (clearance hole)

= 0.45 (untreated surfaces)

ne = no of effective interfaces

Fo= proof load

21

COMBINED SHEAR AND TENSION

(a) Bearing Bolts

(a) HSFG Bolts

0.1

22

db

b

db

sb

T

T

V

V

0.1

22

df

f

df

sf

T

T

V

V

22

Block Shear

BLOCK SHEAR FAILURE

T

A

B C)()( 5.06.0 BCeyABey ApApT

Capacity=Shear Capacity of AB + Tension Capacity of BC

3

Tdb = ( Avg fy /( m0) + 0.9Atn fu /m1 )3

3

Tdb = (0.9Avn fu /( m1) + Atg fy /m0 )3

or

23

24

GENERAL ISSUES IN CONNECTION DESIGN

M =

Td

Standard Connections

(a) moment connection

(b) simple connection

eV

T

C

dV

(a) (b)

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

25

COMBINED SHEAR AND MOMENT IN PLANE

Bolt group eccentrically

loaded in shear

Pri

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 ri

2

• Bolt shear due to M

Rmi=M ri/ ri2

22sincos imiyiimixii RRRRR

2

22

2

22 )()( ii

iy

ii

ixi

yx

Mx

n

P

yx

My

n

PR

Combined shear

26

27

COMBINED SHEAR AND MOMENT OUT-OF-PLANE

Bolt group resisting out-of-plane moment

Ti

d l

i

L

iN

Ad/

6

L

i

(a) (b) (c)

C

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)+shear28

BEAM AND COLUMN SPLICE

Bolted Beam Splice

(a)Conventional

Splice

(b) End-Plate

Splice

Strength, stiffness and ease in erection

Assumptions in

Rolled-section

& Plate Girders

Column Splices – bearing type or HSFG moment splices29

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.

30

V

BEAM-TO-COLUMN CONNECTIONS

Simple beam-to-column connections a) Clip and seating angle

b) Web cleats c) Curtailed end plate

e(a) (b) (c)

(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)31

BEAM-TO-COLUMN CONNECTIONS

Rigid beam-to-column connections

a) Short end plate

b) Extended end plate

c) Haunched

column web

stiffenersdiagonal

stiffener

web

plate

(a) (b) (c)

32

BEAM-TO-BEAM AND

TRUSS CONNECTIONS

(a) Apex Connection

Truss Connections

(b) Support connection

Gusset Plate

Splice

plate

GussetPlate e

suppor

t

Beam-beam connections similar to beam-column connections

Moment continuity may be obtained between secondary beams

Check for torsion in primary beams

33

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

34

Thank You

35

36

Design Example 1: Design a bolted connection

between a bracket 8 mm thick and the flange of

an ISHB 400 column using HSFG bolts, so as to

carry a factored vertical load of 100 kN at a

distance of 200 mm from the face of the column

as shown in Fig. E1.

Solution:

1) Bolt force:

Px = 0; Py = 100 kN;

Total eccentricity x’=200+250/2=325 mm

M = Pyx’ = 100x325 = 32500 kN-mm

TRY THE ARRANGEMENT SHOWN IN FIG. E1

NOTE: MINIMUM PITCH = 60 MM AND

MINIMUM EDGE DIST. = 60 MM

37

2) Bolt capacity

Try M20 HSFG bolts

Bolt capacity in single shear = μf n Kh Fo = 0.48 × 1.0 × 177 =

85 kN

ISHB 400 flange is thicker than the bracket plate and so

bearing on the

bracket plate will govern.

Bolt capacity in bearing = d t pbg = 20 × 8 × 650 × 10-3 = 104

kN

∴ Bolt value = 85 kN > 81.79 safe.

38

Design Example 2: Design a

bolted splice for an ISMB 450

section to transfer a factored

bending moment of 150 kN-m

and a factored shear of 100 kN.

Assume that the flange splices

carry all of the moment and that

the web splice carries only the

shear.

39

SOLUTION:

1) FLANGE SPLICES :

FLANGE FORCE =BM/(D-TF) =

150 × 103/(450-17.4) = 346.7 KN

40

Slip resistance per bolt = 0.33 × 183 = 60.4 kN

Bearing resistance on flange per bolt = 20 ×17.4 × 650 × 10-3 = 226.2 kN

Bolt value = 60.4 kN

Use 3 rows of 2 bolts at a pitch of 60 mm

Flange capacity = (250/1.10) × 1844 × 10-3 = 400.9 kN > flange force OK

Try 150 mm wide splice plate

Thickness of splice plate required

= 346.7 × 103/1.0 × 250(150-2 × 22)/1.10 = 15.8 mm Use 16 mm

Use flange splice plate of size 400×150 × 1641

2) Web Splice

For M20 HSFG bolts of Gr.8.8 in double shear Slip resistance per

bolt = 2 ×60.4 = 120.8 kN

Try 8 mm thick web splice plates on both sides of the web.

Bearing Resistance per bolt = 20 × 9.4 × 650 × 10-3 =122.2 kN

Bolt value = 120.8 kN

Try 3 bolts at 100 mm vertical pitch and 45 mm from the center

of joint.

Horizontal shear force on bolt due to moment due to

eccentricity= 100 × 45 × 100/(2 × 1002) = 22.5 kN

Vertical Shear force per bolt = 100/3 = 33.3 kN

Resultant shear force = √(22.52+33.32) = 40.2 kN < 120.8 (bolt

cap) OK

Use web splice plate of size 270×160×8 - 2 nos. 42

DESIGN EXAMPLE 3: DESIGN A SEATING ANGLE

CONNECTION FOR AN ISMB 400 BEAM TO AN ISHB 200

COLUMN SO AS TO TRANSFER A SHEAR OF 200 KN.

43

1) Seating Angle

The support reaction acts as a UDL over length (b+ 2.5h2) on

the web

Length of bearing required at root line of beam (b+2.5 h2)

= V/(twpyw)= 200 × 103/(8.9 × 250/1.10) = 98.9 say 100 mm

Length of bearing on cleat = b = 100-2.5 h2 =25 mm

end clearance of beam from the face of the column c=

5mm

allow tolerance d = 5 mm

minimum length of angle leg required for seating = b+c+d

= 35 mm

Try ISA 110×110×15 angle of length w = bf = 140 mm 44

Distance from end of bearing on cleat to

root of angle (A to B) = b + c + d - (t+r) of angle;

= 25 + 5 + 5 – 25 = 10 mm

assuming the load to be uniformly distributed over the

bearing length b

moment at the root of angle =(200/10)× 102/2 = 1.0 kN-m

Moment capacity = (250/1.1)×(140×152/4) ×10-6

= 1.79 kN-m > 1.0 kN-m OK

Shear Capacity of outstanding leg of cleat

= [(250/1.10)/1.732]× 140×15×10-3

= 275.5 kN >200 kN OK

45

2) Connection of seating angle to column flange

Bolts required to resist only shear

Try 4 bolts of 22 mm dia and grade 4.6, capacity = 52.7kN/bolt

Total shear capacity = 4×52.7=210.8 kN > 200 kN OK

3) Provide nominal clip angle of ISA 50 × 50 × 8 at the top

46

Design Example 4: Design a bolted web cleat

beam-to-column connection between an ISMB

400 beam and an ISHB 200 @ 40 kg/m column.

The connection has to transfer a factored shear

of 150 kN. Use bolts of diameter 20 mm and

grade 4.6.

47

1) THE RECOMMENDED GAUGE DISTANCE FOR COLUMN FLANGE IS 100

MM.

THEREFORE REQUIRED ANGLE BACK MARK IS 50 MM.

USE WEB CLEATS OF ISA 90X90X8 GIVING GAUGE

G = 50+50+8.9=108.9 MM

(G FOR ISHB200 IS 100 MM )OK 48

2) Connection to web of beam- Bolt capacity

shear capacity of bolt in double shear = 2×160×245×10-3=78.4 kN

bearing capacity of bolt on the beam web = 418×20×9.0×10-3=

75.24 kN

bolt value = 75.24 kN

Try 4 bolts as shown in the Figure with vertical pitch of 75 mm

Assuming the shear to be acting on the face of the column, its

eccentricity

with the centre of the bolt group will produce horizontal shear forces

in

the bolts in addition to the vertical shear.

49

horizontal shear force on top bolt due to moment due to

eccentricity e

= Px e ri/Σ ri2

= 150×50×112.5/2(37.52+112.52) = 30.0 kN

vertical shear force per bolt = 150/4 = 37.5 kN

resultant shear = √(30.02+37.52) = 48.0 kN < bolt value Safe !

50

3) Connection to column flange: Bolt capacity

shear capacity of bolt in single shear = 160×245×10-3 = 39.2 kN

bearing capacity of bolt on column flange = 418×20×9.0×10-3=

75.24 kN

bolt value = 39.2 kN

Try 6 bolts as shown in the Fig.E5 with vertical pitch of 75 mm

4) Check bolt force

Similar to the previous case, the shear transfer between the beam

web and the angle cleats can be assumed to take place on the

face of the beam web.

51

However, unlike the previous case, no relative rotation is possible between the angle and the beam web.

Assuming centre of pressure 25 mm below top of cleat (point A),

horizontal shear force on bolt due to moment due to eccentricity e

=(V/2)exri/Σri2

= (150×50/2)× 200/(502+1252+2002) =12.9 kN

vertical shear force per bolt = 150/6 = 25.0 kN

resultant shear = √(12.92+25.02) = 28.13 kN < bolt value OK

Use 2 Nos ISA 90x90x8 of length 375 mm as angle cleats

ISA 90x90x8 Length 375mm

52

DESIGN EXAMPLE 5: DESIGN A BOLTED END PLATE

CONNECTION BETWEEN AN ISMB 400 BEAM AND

AN ISHB 200 @ 40 KG/M COLUMN SO AS TO

TRANSFER A

HOGGING FACTORED BENDING MOMENT OF 150

KN-M AND A VARTICAL FACTORED SHEAR OF 150

KN. USE HSFG BOLTS OF DIAMETER 20 MM AND

GRADE 10.9.

53

1) bolt forces taking moment about the centre of the bottom flange and neglecting the contribution of bottom bolts and denoting the force in the top bolts by F

4F× 384 = 150× 103

F = 97.6 kN

tension capacity of M20 bolt = 0.9Fo = 159.3 kN

allowable prying force Q = 159.3-97.6 = 61.7 kN

54

2) design for prying action

try 30 mm thick end plate of width be = 180 mm

distance from the centre line of bolt to prying force n is

the minimum of edge distance or 1.1T√βPo/Py = 1.1× 30 √(2× 512/250) = 55.66 mm

n = 40 mm

assuming 10 mm fillet weld,

distance from center line of bolt to toe of fillet weld b = 60-10 = 50 mm;

moment at the toe of the weld = Fb-Qn = 97.6×50-61.7×40 = 2412 N-m

effective width of end plate per bolt w = be/2 = 180/2 = 90 mm

moment capacity =(fy/1.10)×(wT2/4) =(250/1.10)(90×302/4)=4402 N-m > 2412 N-m Safe !

55

56

THANK YOU

57