Iveco DAILY M.Y. 2012, Body Builder Instructions

Page: 103 / 252

FITTING SUPERSCTRUCTURES
3-5
D
AILY
Printed 603.95.241 Base - 02/2012
Construction of the subframe
While the resistance modulus is a determining value for material stress the inertial moment is significant mainly for flexion rigidity
as well as for the ratio of flexing moment to be sustained, according to the connection used.
3.1.3 Aluminium subframe
When materials having different characteristics than steel are used (e.g. aluminium) the size and structure of the sub-frame must
be adapted appropriately.
a) When the task of the sub-frame is mainly to provide a uniform distribution of the load while the chassis maintains the
fundamental task of providing resistance, longitudinal aluminium profiles can be used, having a size identical to that used for steel.
Some typical examples are fixed trays, vans, tanks, provided that supports are continuous and close to each other, or located
in proximity of the suspension supports. Cases when excessive stress on the chassis requires relatively big sizes of steel
reinforcing profiles or shear resistant connections are exceptions.
b) When the sub-frame must also provide support in resistance and rigidity (for example structures with high concentrated loads,
tilting bodies, cranes, central axle trailers, etc.), using aluminium is not recommended and it must be authorized from time to
time by IVECO.
Furthermore, when calculating the minimum size of reinforcing profiles, the allowed stress limit of aluminium must be taken into
account as well as the different elasticity modulus compared to steel (approx. 7,000 kg/mm
2
compared to 21,000 kg/mm
2
of steel),
which requires greater sizes for the profiles.
Similarly: when the connection between chassis and sub-frame is such as to ensure the transmission of shearing forces (connection
with plates), the new neutral axis must be defined when verifying the stress at the two extremities of the single section, according
to the different elasticity modulus of the two materials.
This application for aluminium therefore requires large sizes, scarcely convenient.