Page 23 - Mechanical Engineer's Data Handbook

12 MECHANICAL ENGINEER'S DATA HANDBOOK

I
+,MI
I
\
I
f
P 0 I
P
P
Efficiency of joint:
least of P P P P
PI2 I]. = 4x1~%
QpPt
P
Butt joint
PI2
The rivet is in 'double shear', therefore P, =z,nD2/2
per row.
I
Crushing stress 3D2
In practice, P, is nearer to TJC-.
8
Q, = P/Dt
I .2.4 Rivets and riveted joints in shear

Lap joint

Symbols used:
t = plate thickness
D=diameter of rivets
L=distance from rivet centre to edge of plate Several rows of rivets
p=pitch of rivets
oP = allowable tensile stress in plate The load which can be taken is proportional to the
ob =allowable bearing pressure on rivet number of rows.
t, = allowable shear stress in rivet
T~ = allowable shear stress in plate 1.2.5 Strength of welds
P =load
A well-made 'butt weld' has a strength at least equal to
that of the plates joined. In the case of a 'fillet weld' in
shear the weld cross section is assumed to be a 45"
right-angle triangle with the shear area at 45" to the
plates. For transverse loading an angle of 67.5" is
assumed as shown.
For brackets it is assumed that the weld area is
flattened and behaves like a thin section in bending.
For ease of computation the welds are treated as thin
lines. Section 1.2.6 gives the properties of typical weld
Allowable load per rivet: groups.
Shearing of rivet P, =T,RD~/~ Since fillet welds result in discontinuities and
Shearing of plate P, = tp2Lt hence stress concentration, it is necessary to use
Tearing of plate P, = ap(p - D)t stress concentration factors when fluctuating stress is
Crushing of rivet P, = abDt present.