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CONNECTIONS
RAJU SHARM A
ASSISTANT PROFESSOR
DEPARTMENT OF CIVIL ENGINEERING
CHANDIGARH UNIVERSITY
GHARUAN, M OHALI
DSS-I
Chapter-2
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Connections
Connections
Riveted
Bolted
Welded
Subjected to axial and eccentric load
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The design of connection is very important becausethe failure of joint is sudden and catastrophic.
Following three types of connections my be made bysteel structures:
Riveted
Bolted
Welded
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Riveted Connections
Riveted Connection
Riveting is a method of joining together pieces of metal by
inserting ductile metal pins called rivets into holes of pieces to beconnected and forming a head at the end of the rivet to prevent
each metal piece from coming out
Rivet hole are made in the structural member to be connected by
punching or by drilling.
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Disadvantages of Riveted connections
a) It is associated with high level of noise pollution
b) It needs beating the rivet to red hot
c) Inspection of connection is skilled work
d) Removing poorly installed rivets is costly
e) Labour cost is high
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Bolted
A bolt is a metal pin with a head formed at one end and
shank threaded at the other in order to receive a nut.
Bolts are used for joining together pieces of metal by
inserting them through hole in the metal and tighteningthe nut at the threaded ends..
Bolts are classified as:
Unfinished (Black ) Bolts
Finished (Turned) Bolts High Strength Friction Grip (HSFG) Bolts
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Unfinished/Black Bolts
These bolts are made from mild steel rods with square or hexagonal head.
The shank is Left unfinished i.e. Rough as rolled. Black hole of nominal
diameter of sizes 12,16,20,22,24,27,30 and 33 and 36 mm are available.
These bolts are designated as M16,M20,M20,M24 etc. IS 1364 part 1
gives specifications for such bolts. The shanks of black bolts are
unfinished, the bolt may not establish contact with structural member at
entire zone of contact surface. Joints remain quite loose resulting into
large deflections. The yield strength of commonly used black bolts is 240
N/mm and ultimate strength 400 N/mm.
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High Strength Friction Grip Bolts (HSFG)
The HSFG bolts are made from high strength steel rods. The
surface of the shank is kept unfinished as in the case of black
bolts. These bolts are tightened to a proof load using calibrated
wrenches. Hence they grip the members tightly. If the joint is
subjected to shearing load it is primarily resisted by frictional
force between the members and washers. The shank of the bolt is
not subjected to any shearing. The result into no- sllipage in the
joint. Hence such bolts can be used to connect members subjected
to dynamic loads also
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Classification of Bolts based on Type of Load
Transfer
a) Bearing Type
b) Friction Group Type
Unfinished (black) bolts and finished (turned) bolts belong to
bearing type since they transfer shear force from one member
to other member by bearing, whereas HSFG bolts belong to
friction grip type since they transfer shear by friction.
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Advantage of HSFG Bolts over bearing type Bolts
1. Joints are rigid i.e; no slip take place in the joint
2. As load transfer is mainly by friction, the bolts are not
subjected to shearing and bearing stresses.
3. High static strength due to high frictional resistance
4. High fatigue strength since nuts are prevented from loosening
and stress concentrations avoided due to friction grip
5. Smaller number of bolts result into smaller sizes of gusset
plates
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Disadvantages of HSFG Bolts
1. Material cost is high
2. The special attention is to be given to workmanship especially
to give them right amount of tension
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Advantages and Disadvantages of BoltedConnection
Making joint is noise less
Do not need skilled labour
Need less labour Connection can be made quickly
Structure can be put to use immediately
Accommodates minor discrepancies in dimensions
Alterations, if any ,can be done easily
Working area required in the field is less
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Disadvantages
1. Tensile strength is reduced considerably due to stress
concentrations and reduction of area at the root of the thread
2. Rigidity of joints is reduced due to loose fit, resulting into
excessive deflections.
3. Due to vibrations nuts are likely to loosen, endangering the
safety of the structures.