3-4 BUILDING & MOUNTING THE STRUCTURES E UROCARGO Euro 4/5 3.1.2 Material (aluminum subframe) In the case of materials, having different characteristics compared to steel, such as aluminium, both the dimensions and the struc- ture of the subframe will have, as a rule, to be adapted accordingly. When the subframe’s main function is mainly to distribute the load more evenly while leaving the major loadbearing to the frame, aluminium longitudinal runners can be used having the same dimensions as stated for the steel. Some typical examples are: fixed bodies, box bodies, tanks with continuous and close spaced bearers or bearers mounted directly over the suspension hanger brack- ets.
Exceptions are those cases where the high stresses on the vehicle’s frame demand steel runners of a high dimension or shear-re- sistant connections. When the subframe must contribute in terms of strength and stiffness (bodies having high concentrated loads, such as tippers, cranes, central axle trailers, etc.) aluminium is not recommended and has therefore to be authorised for each application. It should be remembered that, when stating the minimum dimensions for the reinforcement runners, besides the admitted limit of stress for the aluminium, the different elastic modulus compared to steel (approx. 7,000 kg/mm 2 as against 21,000 kg/mm 2 for steel) will also have to be considered.
This will result in larger dimensions for the runners. Similarly, when the connection between frame and counterframe guarantees the transmission of shearing forces (connection via plates), a new neutral axis must be defined for the section based on the different elastic modulus of both materials when checking the stresses at both ends of the single section. In the final analysis, if the subframe has to contribute to the frames Strength / stiffness, higher sectional dimensions for the runners must be used if aluminum in to be used instead of steel. Subframes and bodies Base - January 2008 Print 603.93.431