## 2 Materials and Methods  
From a mathematical point of view, the frame of the electric garbage truck, Bogdan ERCV27 (Figure 1), is a solid body, which in modeling can almost strictly be described as a set of geometrically similar elements, connected in such a way that they form a structure as close as possible in shape to a real body. The frame model produced in the Ansys environment is presented by beams and surfaces, with the structural parts fully corresponding to the drafts (Figure 2) and technical documentation. The chosen approach to build a beam model, rather than a solid model, is explained by the flexibility in terms of its future optimization, namely that the structural elements (rods) can be easily replaced by others (cross-section). The rod model consumes a lot less computational resources than solid models, due to a different finite element meshing approach being adopted (which will be demonstrated below). The beam model produced in the Ansys environment is perfectly suited to the Static Structural Ansys module (Figure 3), in regard to the boundary conditions applied. Figure 1: Bogdan ERCV27 garbage truck. A feature of the model is the use of an electric powertrain instead of a traditional internal combustion engine, so we can see a vertical cabinet for the batteries behind the driver's cabin (Figure 3). The spatial frame itself is fundamentally different from typical primitive truck frames, in that the frame is formed of two longitudinal spars connected by crossbars. The next step is the meshing of the beam model (Figure 4), which consists of the following:  
- 61,233 elements;  
- 71,169 nodes. Figure 3: Ansys module showing the Bogdan ERCV27 garbage truck. Figure 2: The overall dimensions of the Bogdan ERCV27 garbage truck. Unlike solid elements, beam elements correspond, in terms of their two dimensions (height and width), to the cross-section of the pipe and the third parameter (depth) is editable in order to establish the necessary accuracy for the calculation. There is a recommended rule: the depth (mm) must be less than the smallest size of the pipe cross-section. As part of this calculation, a value of 18 mm was set, which was less than the 22.797 mm recommended by the Ansys software. Decreasing this parameter leads to an increase in the calculation time, erasing the advantages of the beam approach compared to the solid model approach. It is obvious that if a solid model was used instead of a beam model, the number of finite elements would be 10\(\times\) greater, which would significantly complicate further strength optimization, which consists of many iterations (step-by-step improvements to the structure). Figure 4: Meshed beam model of the Bogdan ERCV27 garbage truck: (**a**) rear part; (**b**) front part. The customer specifies the material of the spatial frame, in this case 1.4003 (stainless ferritic, chromium steel X2 CrNi12), although the calculation methodology proposed below assumes the possibility of using any grade of steel, which can be imported into the Ansys Granta EduPack module. Among the characteristics that determine the physical and mechanical properties of the material, those detailed in the following table have the greatest role (Table 1). A static calculation is a basic type of structural strength test, which was used even before the creation of solid models (that is also why the model makes sense), drawings, and design documentation. Its main task is to optimize the structure and strength of the spatial frame, reduce the maximum stresses in the model, achieve uniform strength, and improve the capacity of the material. The two main modes of static tests are <<bending>> and <<torsion>>. They are not related to bending or torsional moments, but are related to the type of load applied and the final deformation of the body. In fact, in each of these load modes, the spatial frame is in a complex loaded state, where tensile and compressive forces, as well as torsional and bending moments, are present, this is called a stress-strain state.