CONNCETIONS: -
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Various elements on
a Steel Structure like tension and compression & flexural of members are connected
fasteners Connectors.
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The need of
designing Connections are: -
1)
To connect plates, angles,
channel, I-Sections etc;
2)
To connect different members at
the ends.
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The connections are
generally provided in the following cases:
1)Unless
the requirement to account for the heavy load and long span is met, then the
built-up parts must be given. In this case, to get a good section this section
should be connected together.
2)
The length of the standard section needs to be connected to another section in
case of longer duration. In this case it is necessary to attach the proper
design of multiple parts of the connections.
3)
At the end the different members need to be linked (e.g. secondary beams to be
linked to primary beams, columns, footings, etc.)
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Design of
connections are very important because the failure of joints is Sudden and catastrophic.
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Normally, a connection
failure is not as ductile as that of a Steel member failure.
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Connections may be
classified according to the following:
a) Method of
Fastening (rivets, bolts, welding)
b) Connection Rigidity (rigid, Simple,
Semi-rigid)
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According to IS
code, based on rigidity connection, the joint can be defined as:
1) Rigid
2) Simple
3) Semi-rigid
Semi-Rigid: -
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Semi-rigid
connections have sufficient rigidity to hold the original angles between
members.
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In reality all the connections
will be Semi-Rigid.
Types of Connections: -
The
following three types of connections may be made in steel connections:
1) Riveted Connections
2) Bolted Connections
3)
Welded Connections
1) Riveted Connections: -
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When members of a Structure are created using
Rivets, the joints so far are known as “Riveted Joint" and the process of
jointing is known as “Riveting".
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Rivet is made up of
a round ductile Steel bar or body Called “Shank” and a head at one end.
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Head can be of
different shapes.
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Rivet holes are
made in Structural member to be connected by punching or drilling.
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Size of hole is
greater than rivet Size (1.5-2 mm).
ASSUMPTIONS FOR THE DESIGN OF RIVETED JOINT: -
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The process for
designing a riveted joint is simplified by making the following assumptions and
by taking the protection of the joint into consideration.
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The load shall be
distributed equally to all the rivets.
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Plate stress is
thought to be even.
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Shear stress is
believed to be distributed evenly over the total rivet field.
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The bearing tension
is assumed to be identical between the plate and rivet contact surfaces.
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Bending stress is
ignored in rivet.
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The rivet hole is
expected to be filled to the full.
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Friction between
plates is ignored in the rivet.
Classification based on Shape of Rivet Head: -
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The rivets are
classified on the basis of shape of rivet heads are as follows:
Classification based on method & placing of Rivets: -
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The rivets are
classified on the basis of methods & placing of rivets are as follows:
(i)
Power-Driven Shop Rivet: -
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The rivets which are
driven by hydraulically in the Shop under Control condition is called as Power-Driven
Shop Rivet.
(ii)
Hand Driven Shop Rivet: -
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The rivets which are
driven by hand in the shop is called as Hand Driven Shop Rivet.
(iii)
Field Rivet: -
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The Rivets which
are driven at the place of work is called as Field Rivet.
(iv)
Hot Driven Rivet: -
Ø
The Rivets which are
heated to red hot before driving is called as Hot Driven Rivet.
(v)
Cold Driven Rivet: -
Ø
The Rivets which
are driven at room temperature and high Pressure is called as Cold
Driven Rivet.
Ø=
Nominal Diameter.
D= Grip Diameter.
|
Grip length > [d x (diameter of rivet)]
|
SPECIFICATION FOR DESIGN OF RIVETED JOINT: -
1)
Members
meeting at Joint: -
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At one point the
centroid axes of the members meeting at a joint should coincide and, if there
is any eccentricity, sufficient resistance in the relation should be given.
2)
Centre
of Gravity: -
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The centre of gravity
of rivet will be on the load action line whenever necessary.
3)
Pitch:
-
a)
Minimum pitch: -
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The distance between
opposite rivet centres should be no less than 2.5 times the rivet 's gross
diameter.
b) Maximum
pitch: -
Ø
The average pitch
does not exceed 12 t or 200 mm whichever is less in the member of the
compression and 16 t or 200 mm whichever is less in the case of the members of
the stress when the rivet line lies along the force action axis. Unless the
rivet line does not lie along the force line of operation, its maximum pitch
does not exceed 32t or 300 mm, whichever is less, where t is the outside plate
thickness.
4)
Edge
Distance: -
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The rivet joint
provides a minimum edge gap of about 1.5 times the gross diameter of the rivet
measured from the middle of the rivet hole.
Advantages of riveted connections: -
1) Easy in riveting process.
2) Rivet connection is permanent in nature.
3) Cheaper fabrication cost.
4) Low maintenance cost.
5) Dis similar metals can also be joined.
6) Rivet connection is possible without electricity in
remote area.
Disadvantages riveted connections: -
1) Necessity of pre-heating the rivets prior to driving.
2) High level of noise pollution.
3) Skilled work necessary for inspection of connection.
4) Cost involved in Careful inspection & removal of
poorly installed Rivets.
5) Labour Cost is high.