Document No: DELTA SIGMA-USM
Version 4
Revision 3.94.2
Page: 30 / 32
L = Stressed Length of the Bolt
The stressed length of the bolt is equal to the actual clamped length of the bolted
connection plus that portion of the bolt within the head and nut, which experiences
tensile stress. A number of theories have been proposed as to the stressed length
within the head of the bolt and the within the nut. However, testing by use of the
calibration function of the Delta Sigma reveals that no single theory is valid for all
bolt configurations.
Thus, for the estimation of the Load Factor discussed here, it is sufficient to assume
that the approximate stressed length is equal to the clamp length of the joint plus the
nominal bolt diameter. The Load Factor (elongation in N per 0.1 of a mm is
calculated by solving the above equation for Hooke’s Law while setting the value of
the elongation at 10.
Worked example for a bolted joint in Metric units:
Data: M20 x 2,5: ISO 8.8 Stud Bolt with and 200 mm effective length (clamp nuts & washers):
E (Youngs Modulus) for 8.8
= 206,15 kN/ mm²
A (Iso for M20)
= 245 mm²
L- Effective length
= 200 mm
Hence the load factor entered into the DS for this bolt joint example would be: 25333
Note: It should be noted that this estimation is inherently less accurate than calibration of the actual Load Factor
by using actual known loads which correspond to measured elongation.
L L
D
g
=
+
(
)
D
L
AE
L
AE
LF
LoadFactor
g
+
=
=
=
100
100
mm
kN
mm
N
x
x
LF
LoadFactor
/
3
,
253
1
.
0
/
25333
200
)
15
,
206
245
(
100
=
=
=
=