11.1 TYPE OF RIVETS
The commonly used rivet is known as solid-shank type (Figure 11.2) and is
driven into the rivet hole using a bucking bar. It is identified by the material,
head, shank diameter, and temper conditions.
Figure 11.2: Solid shank rivet
11.2 METHOD OF RIVETING
The second head formed is called a shop head and is achieved by cold
riveting, hot riveting, or automated riveting to give different characteristics.
Before use, a hot riveted seam would undergo testing and any leaking rivets
were repaired with a metal ‘caulking’ tool. This process which beats down
the edge of the rivet leaves tale marks around the rivet head that could be
seen on some of the objects.
Think and Try !
Which riveting method is likely to be leak proof and explain why?
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grip
before head formation
Figure 11.3: Riveting process
11.3 TYPE OF RIVET HEADS
The different heads are roundhead, flathead, countersunk head etc. as shown
in Fig. 11.4 used for general purpose, boilers and structures. The temper
condition and strength are marked on the head of the rivet.
General purpose rivets (below 12mm diameter)
General purpose rivets (above 12mm diameter)
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Rivets for boilers
Figure 11.4: Types of rivet heads
11.4 RIVET MATERIALS
Low carbon steels (C10, C15 etc.) are used as rivet material for joining steel
parts. The corrosion-resistant monel, copper, brass, aluminium etc. are used
for riveting where corrosion- resistant and light weight are the requirement.
Metal temper is an important factor in the riveting process. The rivet must be
soft, or comparatively soft, before a good head can be formed. A factor of
safety of 2 to 4 is used in case for rivets of plain carbon steel on the basis of
the yielding failure criterion.
11.5 TYPES OF RIVETED JOINTS
Riveted joints are classified in lap and butt joints on the basis of their
construction In lap joint, there exists an overlap between two ends of plates
and the one or more number of rows of rivets passes through both the plates
to hold them together. These plates will be called main plates henceforth.
Figure 11.5 shows the general arrangement of plates and load in the lap
joint. The load in this case behaves as it is eccentric and produces a bending
moment which tends to bend the rivet and make the line of action of forces
collinear as shown in the figure.
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F
F
F
F
F
F
Figure 11.5: Lap joint
The disadvantage of lap joint discussed above is removed in butt joint where
the main plates are kept in alignment and butt strap or cover plates (one side
or both sides) are placed. The rivet in the case of butt joint passes through
one of the main plates only. If the cover plate is provided on one side then it
is called single cover Butt joint and if this cover plates are provided on both
sides then it is called double cover Butt joint. Then they are further classified
as single riveted single cover Butt joint, Double riveted single cover Butt
joint, single riveted double cover Butt joint, Double riveted double cover
bolt joint all these are shown in Figure 11.6.
Figure 11.6: Butt joint
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11.5.3 Nomenclature
The complete nomenclature of any riveted joint also includes the type of
riveting (chain or zig-zag), rows of rivet and number of cover plates in case
of butt joint. The width of double cover plate butt joint can also vary in some
cases. It is important to note that the term single riveting means one row of
rivets in a lap joint or one row in each side of a butt joint; double riveting
means two rows of rivets in a lap joint or two rows on each side of the joint
in butt riveting. Lap joints may also be made with inside or outside cover
plates. Figure 11.7 shows different riveted joints with full name which are
self explanatory.
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Figure 11.7: Different riveted joints
11.6 SIZE AND TYPE OF HOLE
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Rivet hole may be punched or punched and reamed, or drilled. It is usually
made slightly larger than rivet diameter (Table 11.1). In some cases, the
holes are reamed to provide minimum clearance so that the rivet fills the
hole completely especially in cold driven rivets in automatic machine. When
holes are punched in heavy steel plate, there may be considerable loss of
strength unless the holes are reamed to remove the inferior metal
immediately surrounding them. Annealing after punching tends to restore
the strength of plate in the vicinity of holes.
Table 11.1
Rivet diameter
12.0 14.0 16 18 20 22 24 27 30 33 36 39 42 48
Hole diameter (boiler)13.0 15.0 17 19 21 23 25 28 31.5 34.5 37.5 41 44 50
Hole diameter
(general)
13.5 15.5 17.5 19.5 21.5 23.5 25.5 29 32 35 38 41 44 50
11.7 FAILURE OF RIVET AND PLATE
A riveted joint is said to be failed if either the rivet or plate are failed. In
designing the riveted joint the main parameters to be set are pitch, number of
rows, type of riveting when we design it for pressure vessels and
arrangement of rivets for structural joints.
It is also important to note that for given value of load on the joint, we can
find the total numbers of rivets required for the joint and in case when load
is not known we will design the joint on the basis of the strength of the joint
in one pitch length.
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Generally, load is known in case of structural joints and it is not directly
known in problems related to pressure vessels or boilers in particular. Hence
we will develop different equations for one pitch length. Before discussing
cases of pressure vessel and structural joints, we shall first discuss the
different modes of failures of a riveted joint and then we can apply these
equations for specific cases.
11.7.1 Tearing of plate
A plate may fail in tearing between adjacent rivets in the same row or
adjacent rows (Figure 11.8). If hole diameter (d), plate thickness (t) and
the design tearing strength ( σ dt ) are known, the tearing resistance of the
plate is given by
Ft = ( p − d )(t )(σ dt )
11.1
Figure 11.8: Tearing of plates
In case of the riveted joint in which the width (w) of the plate is known the
equation is written in following form
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11.2
F = (w − nd )t (σ dt )
Where
n
is the number of rivets in the row along which tearing is
considered.
11.7.2 Crushing of rivets/plates
The rivets fail in crushing as shown in Figure 11.9. If the rivets and plates
are made of the same material then crushing may take place at the contact
area of rivet and plate. As due to the cylindrical contact the distribution of
the bearing stress is not uniform, hence, the projected area will be used for
computation of crushing/bearing stress. The failure is assumed when either
of the main plates of thickness t, have crushed or cover plates of thickness tc
(both cover plates in case of double cover butt joint) have crushed. So, the
crushing strength is given by
For lap joint
Fc = dtσ dc
11.3a
For single cover butt joint and
t < tc
Fc = dtσ dc
11.3b
For single cover butt joint and
t > tc
Fc = dtcσ dc
11.3c
Fc = dtσ dc
11.3d
Fc = d (ti + to )σ dc
11.3e
For double cover butt joint and
t < (ti + to )
For double cover butt joint and t > (t i + t o )
Where t i and t o are thicknesses of inner and outer cover plates respectively.
These equations also consider the number of rivets as required for specific
case.
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Figure 11.9: Crushing failure of rivete/plate
11.7.3 Shearing of rivets
The rivet will fail in single shear for lap joint and butt joint with one strap or
cover plate and the rivets will fail in double shear in case of double strap butt
joint as shown in Figure 11.10. The resistance in single and double shear is
given by
π
For single shear
Fs =
d 2τ d
11.4a
For double shear
π

Fs = 1.875 d 2 τ d
4

11.4b
4
These equations also consider the number of rivets as required for specific
case.
(a)
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(b)
Figure 11.10: Shear failure of rivet (a) single shear (b) double shear
11.7.4 Tearing of plates between rivet hole and plate edge
The tearing may also take place when plate tears from hole to the edge of the
plate if the rivets are placed too close to the edge but this type of failure is
avoided by placing the centre of rivet 1.5 times the rivet diameter away from
the edge.
Figure 11.11: Tearing failure of plate at edge
If proper margin from the edge of the plate and each row is kept, then the
failure of a joint is most likely to occur as a result of shear failure of the
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rivets, bearing/crushing failure of plate or rivets or tensile failure of the
plate, alone or in combination. Rivets do not undergo pure shear and would
be subjected to a combination of tensile and shear stress as shown in Figure
11.12. Furthermore, the rivets contract on cooling in case when these are hot
driven. This contraction draws the plate together and gives rise to a frictional
force between plates.
Figure 11.12: Typical failure of rivet in combined shearing and tension
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