The strength structure of a transportation power-driven vehicle is a bars system that builds-up a complex frame, space loaded. Due to the multiple constraints and to the closed geometrical contours, the mechanical system is not only exterior but also interior redundant. In order to evaluate the value of mechanical stresses by analytical calculation, the non-determination must be solved. In this paper the mechanical non-determination calculation is made using the stresses method, only the transverse stress and the torque load will be taken into account.
For a proper structure of the three-axles trucks, the stresses distribution in the component bars will be determined. Thus, the determined calculation will make the basis of an automatic running program that allows the deceleration of different influences of the geometrical and loading parameters over the mechanical stresses. An application will be made on a particular structure using the constructive elements of a heavy transportation power-driven vehicle.
In analyzing the mechanical structure of a heavy transport vehicle it is found that the key element, on which all major elements are mounted, is a metal frame made of rolled steel. Major component parts of the strength are the two struts, cross-linked by a few transverse bars. On struts there are mounted: wheel gear axles, engine, cabin, cargo loading system, according to fig.1. In analyzing the structure’s designed shape it was found that it is leaning in 6 points (wheels), having two closed geometric contours.
To assess the mechanical stress it requires calculation of reactions and efforts. If we consider spatial loads (a certain direction), it appears that mechanical system is three times statically non-determinate outside (reactions in wheels) and twelve times statically non-determinate inside (non-determination of efforts); thus the mechanical assembly of strength is 15 times statically non-determinate. The normal operating regimes of the truck is analyzed, in neglecting the transitional or accidental regimes; thus it is found out that loads are vertical and structure has vertical longitudinal plane of symmetry (geometrically and mechanically).