Steel Connection Methods

8/19/2019 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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Steel Connection Methods

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