Design of connections

Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423 603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade, NBA Accredited, ISO 9001:2015 Certified
Unit I : Design of connections
By
Prof V M Mahajan (Asst. Professor)
Department of Civil Engineering
Email Id: mahajanvalmik@sanjivani.org.in

Connections
 As we know that, A steel structure is an assemblage of different element,
which are connected, fastened to one other. So that they will act together as a
single composite unit.
 Connections acting as a medium for transfer of force, load or moment from one
member to other.
 The following types of connections:
1. Riveted connections
2. Bolted connections
3. Welded connections
4. Pins connections
5. Combination of above
2

Bolted connections
 A bolt may be defined as a metal pin with a head at one end and a shank
threaded at the other end to receive a nut.
 Steel washers are provided under the bolt as well as nut for; distributing the
clamping pressure of the bolted member and to prevent threaded portion of
the bolt from the bearing on the connecting pieces.
3

Classification:
1) Based on force transferred:
a) Concentric connections- load passes through C.G.
b) Eccentric- load away from the C.G.
c) Moment resisting connections- joint subjected to moment-beam and column
2) Based on type of force:
a) Shear connections- lap and butt joint
b) Tension connections- hanger connection.
c) Combined shear and tension- bracing.
3) Based on force mechanism:
a) Bearing type- bolt bear against the hole to transfer the force.
b) Friction type- force is transferred by friction.
4
Bolted connections

Types of bolts
1) Unfinished or black bolt-
 Bearing type of bolt. It also called as ordinary, common, rough bolt.
 Made from mild steel rods with square or hexagonal head.
 Nominal diameter- 16, 20, 24, 30 and 36 are commonly used.
2) Finished or Turned bolt- shank of these bolt is formed from a hexagonal rod.
3) High strength bolts-
 Made from medium carbon heat treated steel and from alloy steel.
 Has high strength two or more times than ordinary bolt.
 Available in size 16mm to 36mm.
5

 Grade 4.6 – M20
 20mm is diameter of bolt
 Ultimate tensile strength = 4x100, fub = 400 N/mm2
 Yield stress = 400x0.6, fyb = 240 N/mm2
 IS 1367 (part – 3)
Advantages:
1) Connections can be made quickly; erection of the structure speedy.
2) Less skilled persons are required.
3) Less equipment are required.
4) Cost is less. 6
Grade of steel fub fyb
3.6 330 180
4.6 400 240
4.8 420 320
5.6 500 300
5.8 520 400
Types of bolts

Types of bolted joint
1) Lap joint-
 Two member are overlapped and connected together.
 It may be single or double bolted lap joint.

2) Butt joint-
2) Butt joint-
 Two member to be connected
are placed end to end.
 Additional plates are provided
on either or one side is known as
cover plates.
7

Failure of bolted joints
Failure may be in bolts or member connected:
1) Shear failure of bolt:
 The maximum factored shear force
in the bolt may exceed the nominal shear
capacity of the bolt.
 Bolt may fail in single or double shear.
2) Bearing failure of plates:
 When member is subjected to shear
force , slip takes place and bolt comes
in contact with plates.
8

3) Bearing failure of bolt:
 Bolt is crushed around half circumference.
 It does not occur in practice except when plates are made of high strength
steel.
4) Tension failure of bolt: Bolts subjected to tension may fail at the stress area.
5) Tension or tearing of plate: it occurs when bolt are stronger than plate.
6) Block shear failure: if bolts are placed at a lesser end distance than required
causing plate to shear out. Block of material within the bolted area breaks.
9
Failure of bolted joints

Specification for bolted joints
1) Pitch of the bolts (P): (IS 800:2007, Cl. No. 10.2.2, page no. 73)
 The distance between centers of two consecutive bolts in row, measured along
the direction of load.
 P shall not be less than 2.5 times diameter of bolt.
 P shall not be exceed 16t or 200mm, whichever is less (tension member)
 P shall not be exceed 12t or 200mm, whichever is less (compression member)
 P shall not be exceed 4.5 d,
for butt joint.
2) Gauge distance (g):
 c/c distance of consecutive bolt of adjacent rows and measured perpendicular
to direction of load.
 g shall not be exceed 100 + 4t or 200mm, whichever is less.
 g shall not be less than 2.5 of dh. 10

3) Edge distance (e): (IS 800:2007, Cl. No. 10.2.4.2, page no. 74)
 It is the distance of center of bolt from adjacent edge of plate.
 e shall not be less than 1.7 times diameter of hole………for hand flame edge.
 e shall not be less than 1.5 times diameter of hole………for machine flame edge.
 e shall not be exceed 12t t= thickness of thinner plate
 e shall not be exceed 40 + 4t
4) End distance (e’ ): same as above
11

Specification for bolted joints

Bearing – type connections
 It is assumed that, the load to be transferred is larger than the frictional
resistance caused by tightening the bolts, consequently members slip a little
over each other, placing the bolt in shear and bearing.
 No. of bolts required is equal to load divided by the strength of one bolt.
 Generally, a minimum two or three bolts are provided even if one bolt is
required.
 The strength of a bolt multiplied with the number of bolts in the joints gives
the strength of joint on the basis of bolts.
 However, the failure of joints can be in bolt or in plate.
1) Shearing strength of bolt’s: (IS 800:2007, Cl. No. 10.3.3, 75)
 The resistance of bolt to shear is called as the nominal capacity of bolt in shear
and denoted by V nsb.
 It depends upon the ultimate tensile strength of bolt fub and no. of shear
planes n.
 The nominal shank area Asb and shear area of bolt at threads Anb in each
shear plane.
12

 The nominal shear capacity of the bolt is given by,
Where,
= No. of shear planes with threads.
= No. of shear planes without threads (shank, plane area)
a) If length of joint (i.e. distance between first row & last row of bolt) exceeds
15d, where d = diameter of bolt, then
Reduction factor is multiplied, (IS 800:2007, 10.3.3.1, 75)
The nominal shank area, Asb =[(π/4)x(d2)] Anb =0.78X[(π/4)x(d2)]
Anb = 0.78 X Asb
13
 
3
bssbnnbu
bsn
AnAnf
V


nn
sn
d
l j
jl
200
075.1 
jl

b) If the grip length (depth) lg exceeds 5d the shear capacity shall be reduced to
(IS 800:2007, 10.3.3.2, 75)
c) If packing plates in excess of 6mm are used the shear capacity should be
reduced to (IS 800:2007, 10.3.3.3, 75)
d) Bolt subjected to combined shear and tension (IS 800:2007, 10.3.6, 76)
Vsb = Vb = factored shear force acting on bolt
Vdb = design shear capacity (10.3.2)
Tb = factored tensile force acting on the bolt and
Tdb = design tension capacity (10.3.5)
14
 
caseanyindexceednotshalllandexceednotshall
ld
d
gjlgl
g
gl
8
3
8




)0125.01( kpkp t
0.1
22












db
b
db
b
T
T
V
V

2) Bearing strength of bolt: (IS 800:2007, Cl. No. 10.3.4, 75)
Nominal bearing strength of bolt;
= diameter of hole
d = diameter of bolt
e, p = edge and pitch
t = thickness of connected plate
= ultimate tensile stress of bolt and plate respectively
Bearing strength
15






 0.1;;25.0
3
;
3 u
bu
oo
b
f
f
d
p
d
e
ofsmallerk
od
ubbpn ftdkV  5.2
ubu ff ,
bm
u
b
bm
bpn
bm
bpn
bp
f
tdk
VV
V

 5.2

3) Tensile strength of bolt: (IS 800:2007, Cl. No. 10.3.5, 76)
Nominal tensile capacity of bolt in tension,
16
om
bm
bsbybnbubn AfAfT


 9.0
bm
bnbu
bm
bn
bd
Af
T
Tif





9.0

Design of connections

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Design of connections

Similar to Design of connections (20)

More from Valmik Mahajan

More from Valmik Mahajan (14)

Recently uploaded

Recently uploaded (20)

Design of connections