[ECE R55 Annex 6]
3.6. Drawbars
3.6.1.1. Test and design forces
Drawbars shall be tested in the same way as drawbar eyes (see paragraph 3.4.). The
type approval authority or technical service may waive an endurance test if the
simple design of a component makes a theoretical check of its strength possible. The
design forces for the theoretical verification of the drawbar of centre axle trailers with
a mass, C, of up to and including 3.5 tonnes shall be taken from ISO 7641:2012. The
design forces for the theoretical verification of drawbars for centre axle trailers having
a mass, C, over 3.5 tonnes shall be calculated as follows:
Fsp = (g × S/1000) + V
where the force amplitude V is that given in paragraph 2.11.4. and S is that given in
paragraph 2.11.3 of this Regulation.
For bent drawbars (e. g. swan neck) and for the drawbars of full trailers, the
horizontal force component Fhp = 1.0 × D shall be taken into consideration.
3.6.2. For drawbars for full trailers with free movement in the vertical plane, in
addition to the endurance test or theoretical verification of strength, the resistance to
buckling shall be verified either by a theoretical calculation with a design force
of 3.0 × D or by a buckling test with a force of 3.0 × D.
The permissible stresses in the case of calculation shall be in accordance with of
this regulation paragraph 3.6.4.
3.6.3. In the case of steered axles, the resistance to bending shall be verified by
theoretical calculations or by a bending test. A horizontal, lateral static force shall be
applied in the centre of the coupling point. The magnitude of this force shall be
chosen so that a moment of
[from TA31]
Fs =
𝟎,𝟑 ∗ Av ∗
L2
B
2
*g
However, in the case where the steered axles form a twin, tandem, axle front carriage
(steered bogie) the moment shall be increased to
[New]
Fs =
𝟎,𝟒 ∗ Av ∗
√A²+B²
2
L2
*g
Figure X3
[from NZ 5446:2007]
Fs =
𝟎,𝟔 ∗ Av ∗((√𝐴²+𝐵²) + T)
L2∗6
*g
is exerted about the front axle centre. The permissible stresses shall be in
accordance with of this regulation paragraph 3.6.1.2.
Fs
g
= Side force [kN]
= the acceleration doe to gravity [m/s²]
A
0,3
0,4
0,6
B
Av
L1
= Axle spacing [m]
For the standard calculation
tandem axle A = 1,35m
tridem axle A = 2,7m
= constant for single axle
= constant for tandem axle
= constant for tridem axle
= Mean track [m] (for the standard calculation B = 2,10m)
= Mass on axle group under consideration [t]
= Distance of the drawbar connected point form the turntable centre [m]
For the standard calculation
single axle L1 = 0,6m
tandem axle L1 = 1m
tridem axle L1 = 2m
L2
= Distance of the tow-eye from the turntable centre [m]
3.6.1.2. Permissible stresses
The permissible stresses based on the design masses for trailers
having a total mass, R or C, over 3.5 tonnes
3.6.1.2.1 Calculation of the permissible stress
[from ISO 7641:2012]
a) Ultimate tensile stress in cross sections without weldings
0,6
σBmin > σc < 0,8 σs
b) Ultimate tensile stress in welded cross sections
0,45 σBmin > σc < 0,65 σs
[from TA 31]
c) Permissible shear stress
𝝉=
𝝈𝒄
√𝟑
d) Permissible effective stress
σ eff. = √(𝝈𝒏 + 𝝈𝒃)² + 𝟑 𝒙 𝝉²
σ eff. <= σc
where
σc is the permissible stress, in N/mm² of the steel grade utilized
σB is the ultimate tensile stress, in N/mm² of the steel grade utilized
σs is the yield stress, in N/mm² of the steel grade utilized
σn is the nominal compressive stress, in N/mm²
σb is the bending stress, N/mm²
[from TA 31]
permissible stress for weld seam
fillet weld: 90 N/mm²
butt weld: 100 N/mm²
3.6.4.
Calculation of the permissible buckling stress
[from TA 31]
σn =
3xD
A
x
L
L2
≤ 𝜎 np
where
σn
D
A
σnp
L
L2
is the calculatory buckling stress [N/mm²]
is the D-value [kN]
is the total sectional area of the test relevant cross section [mm²]
is the permissible buckling stress [N/mm²]
is the total length of the drawbar
is the free buckling length
The permissible buckling stress shall be determined according to Euler and
Tetmajer. Dependent of the slenderness ratio and of the steel grade.
𝐥𝐱
𝛌𝐱 = 𝐢𝐱
𝛌𝐲 =
𝐥𝐲
𝐢𝐲
where
λx , λy is the slenderness ratio with reference to the x-axis and y-axis of the cross
section
lx
ly
is the buckling length in x-axis; (details see fig. XX)
lx = L (if L > l1 ) else lx = l1
is the buckling length in y-axis; (details see fig. XX)
ly = l3 or
ly = 0,7 x l3 if is one crossbar existing
ly = 0,5 x l3 if is two or more crossbar existing
ly = l4 (fig. XX b)
ly = L (fig. XX c)
ix, iy is the radius of gyration of the cross section