Steel Connection Methods
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Transcript of Steel Connection Methods
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The various members of steel frame structure are to be suitably
connected for the transfer of load.
Following are the methods adopted for connecting the members of steel
work.
1. Bolts
2. Rivets3. elding
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The holes are made in the
members to be connected andthe diameter of the holes is
kept about !."!mm larger than
that of e#ternal diameter of
the bolt.
$t may be also adopted when it
is difficult to use rivets as
connecting medium.
Bolts Bolted %oints are one of the most common elements in construction and
machine design. They consist of fasteners that capture and %oin other parts.
& 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. 'teel washers are also provided
under the bolt as well as under the nut.
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Advantages of bolted onnetion (conomy) speed and ease of erection
Reliability of service
(ase of inspection
Fewer) and less highly skilled operators re*uired
+o pre,heating of high strength steels
+o weld cracking or induced internal stresses
T!"es There are several types of bolts used to connect the structural elements. 'ome of
the bolts commonly used are-
1. nfinished bolts
2. Turned bolts
3. Ribbed bolts
/. 0igh strength bolts
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#. $nfinis%ed bolts &'la( bolt)
nfinished bolts are also called ordinary) common) rough or black bolts.
There are used for light structures purlins) bracings) etc. under static loads. They
are not recommended for connections sub%ected to impact load) vibrations andfatigue.
Bolts are forged from low carbon rolled steel circular rods) permitting large
tolerances. rdinary structural bolts are made from mild steel with s*uare or
he#agonal head.
The bolt hole is punched about 1.4mm more than the bolt diameter.
The nuts on bolts are tightened with spud wrenches) producing little tension.
Therefore) no clamping force is induced on the sections %ointed. 'ometimes a hole
is drilled in the bolt and a cotter pin with a castellated nut is used to prevent the
nut from turning on the bolt.
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*. T+rned bolts These bolts are fitted to holes the same diameter as their shank and the bolt is
driven home by hammering and then secured with a nut.
The surfaces of the bolts are prepared carefully and are machined to fit in thehole. Tolerances allowed are very small.
These bolts have high shear and bearing resistance as compared to unfinished
bolts.
They are used where more accuracy in fitting is re*uired and are usually made of
higher grade steel.
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,. ibbed bolts These are also called fluted bolts. The head of the bolt is like a rivet head.
The threaded and nut are provided on the other end of the shank. From the shank
core longitudinal ribs pro%ect making the diameter of the shank more than thediameter of the hole. These ribs cut grooves into the connected members while
tightening and ensure a tight fit. These bolts have more resistance to vibrations as compared to ordinary bolts. The
permissible stresses for ribbed are same as that for rivets.
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Fail+re of bolted onnetions
'hearing of bolts
Bearing failure of plate
Bearing failure of bolt
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Rivet The rivet is other method to connect steel members. These are made from
the round rods of mild steel and consist of a hemispherical bottom shaped
head with a cylindrical shank.
The holes are drilled in the members to be connected and the rivet which isrendered soft by heating) is inserted in the hole. The shank e#tends out of the
prepared rivet hole and the e#tended part is given shape of second head by
riveting machine.
The usual form of rivet had which is cup shaped in appearance is termed as
snap head. &nd to have the second head flush with the plate or member) countersunk
head is eliminated. The diameter of the hole should be
kept about 2mm larger than that of
shank. The distance between consecutive
rivets is termed as pitch.
There are 2 types of rivet-
1. 5ap %oint
2. Butt %oint
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#. La" /oint in rivet The two members to be connected are overlapped and connected together. 'uch a
%oint is called a lap %oint as in below Figure. & single riveted lap %oint and a double riveted lap %oint are shown in Figs b)c
respectively. The load in the lap %oint has eccentricity) as the centre of gravity of
load in one member and the centre of gravity of load in the second member are
not in the same line) as shown in Fig. 2.2d. Therefore) a couple is formed which causes undesirable bending in the connection
and the rivets may fail in tension. To minimi6e the effect of bending in lap %oints
at least two rivets in a line should be provided. &lso) due to the eccentricity the
stresses are distributed un,evenly across the contact area between rivets and the
members to be connected. This puts a limitation on the use of lap %oints.
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*. '+tt /oint in rivet The two members to be connected are placed end to end. &dditional plate7plates
provided on either one or both sides) called cover plates and are connected to the
main plates. as in Figs 2.2e)h. $f the cover plate is provided on one side as in Figs 2.2f) g) it is called a single
cover butt %oint but if the cover plates are provided on both the sides of main
plates it is called a double cover butt %oint as shown in Fig. 2.2.i)%.
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$t is more desirable to provide a butt %oint than a lap %oint for two main reasons-
1. $n the case of double cover butt %oint the total shear force to be transmitted by the
members is split into two parts and the force acts on each half as shown in Fig.
2.2k. But in the case of lap %oint Fig. 2.2$) there is only one plane on which
the force acts and therefore the shear carrying capacity of a rivet in a butt %oint is
double that of a rivet in a lap %oint.
2. $n the case of a double cover butt %oint) eccentricity of force does not e#ist and
hence bending is eliminated) whereas it e#ists in the case of a lap %oint.
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Welding The process of welding has become more popular for providing an effective
method of connecting members of steel,framed structure. &nd it has now
practically replaced rivets.
$t %oins two or more structural members by introducing fused metal into
fillets between them or by raising the temperature and then applying
pressure.
ith the development of welding it has become possible to render
architectural beauty to steel structures also. &ny structural member of
desired pattern can thus be %oined flush to a smooth surface.
There are 2 different methods of welding commonly adopted-
(lectric arc welding- in this) a spark is produced between the welding rod
and the surface to be weld.
#y,acetylene welding- $n this) a flame of high temperature is produced by burning a mi#ture of acetylene and o#ygen.
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Advantages of welding Rapid e#ecution of work
+oise produced during process of riveting is eliminated in welding.
$t is economical when used on a large scale.
$t is possible to give some architectural effect to the steel structure
The angle cleats necessary in riveted connections are not re*uired) thus
saving in material.
&ny structural member of desired pattern can thus be %oined flush to a
smooth surface. There is no reduction in the sectional areas due to holes for rivet and hence)
when welding is adopted) the entire section is considered effective for taking
up the tensile stresses.
T!"es There are two types of welds
1. Butt weld
2. Fillet weld
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#. '+tt weld These welds are used to %oin plates at their edges and the weld metal fills the gap
between them. The section of the butt weld employed depends on the thickness of
the plates to be %oined. The edges of the plates to be %oined are cleaned and shaped as necessary) the plates
are fi#ed in position and the weld metal run in from the filler rod. Thin plates upto "mm thick) re*uires no shaping of edges and weld is formed. 8lates upto 12mm thick) have their edges shaped to form a single 9 butt weld. The
purpose is to allow the filler rod to be manipulated inside the 9 to deposit weld
metal throughout the depth of weld without difficulty. 8lates upto 2/ mm thick) are %oined together either with a double 9 weld or single
as shown in figure. 8lates over 2/ mm thick) are %oined with a double weld. For dis similar plates) single : butt weld is used.
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*. Fillet weld $n this type) the edge of one plate is brought against the surface of another not in
the same place and welding metal is fused in the corner between the two plates.
Thus the %oint can be welded on one or both the sides. Fillet welded %oints such as tee) lap and corner %oints are the most common
connection in welded fabrication
;ifferent shapes of fillet weld
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