## 5 FEM Numerical Tests of the Strength of the Basic Platform and Sets in the Design Version
### Shell-Solid 3D FEM Models--Variants of Basic Loads Occurring at Various Forms of Loading/Unloading
#### 6.1.3 Variant 3  
In Variant 3, the lateral lifting of the platform with a load of the maximum weight of \(\mathrm{Q_{max}}\) was represented using forklifts. Figure 15b shows the schematic support and reduced loads of the platform in Variant 3.  
The support of the platform in this variant of the analysis was represented using the nods described symbolically in Figure 15b. The nods in the platform support model for analysis in Variant 3 were adopted identically to Variant 1 (Section 6.1.1 of the paper).  
Loading the platform with a load during its lifting using the forklift method was represented in the FEM model using reduced loads from an external load in the form of logs and forces from forklifts, represented as continuous loads. Force loads were defined on the lower surfaces of the internal holes in the web stiffeners of the I-beams of the hook device, integrated with the bottom of the platform frame. Continuous loads applied in Variant 3 of the FEM model of the platform are shown in Figure 15b and marked with 1. The values of these load expenditures replacing the fork impact on the platform were determined from the relationship of 1/4.(\(\mathrm{Q_{max}}+\mathrm{Q_{W}}\))/L, where \(\mathrm{Q_{max}}\) is the maximum force of the load weight, \(\mathrm{Q_{W}}\) is the dead weight of the platform, and L is the length of a single hole cut in the web stiffeners of the I-beams of the hook device of the bottom frame of the platform as marked in Figure 15b.  
Figures 17-19 show maps of reduced H-M-H stresses for variants, respectively: Variant 1, Variant 2, and Variant 3, paying particular attention to the effort in the area of removable joints between the end carriage and I-beams of the hook device under the platform frame.  
Figures 20 and 21 show the views of deformations and maps of displacements determined in the platforms lifted with the load by forklift (Variant 3) and by hook (Variant 4), respectively.  
Figure 22 shows maps of reduced H-M-H stresses in Variant 4 of the load corresponding to the loading of the prototype platform with the Q\({}_{\text{max}}\) load using a hook device. Figure 22a shows the enlarged effort of the connection area of the removable joints between the end carriage and I-beams of the hook device under the platform frame. Figure 22b shows the area of maximum platform effort in Variant 4 of operating loads--hook loading of the platform with logs with the Q\({}_{\text{max}}\) weight. The maximum H-M-H stress values equal to \(\sigma_{\text{max}}=370.2\) MPa (Figure 22b, Table 4) occur in the solid elements in the area of the connection of the end carriage side wall and the side brace holding the end carriage in the vertical position. The concentration of stresses in this area, exceeding the permissible stresses R\({}_{\text{dop}}=120\) MPa, is caused by the use of a simplified representation of the bolt connection by means of a node-node connection in the kinematic model of the articulated  
Figure 19: Map of reduced H-M-H stresses for Variant 3 when lifting with forks—\(\sigma_{\text{max}}=94\) MPa.  
Figure 18: Map of reduced H-M-H stresses for Variant 2 when lifting the platform with ropes—\(\sigma_{\text{max}}=151.71\) MPa.  
coupling. The maximum H-M-H stresses in the joined elements of the end carriage and side brace outside the area of this joint do not exceed 130 MPa.  
Figure 21: Map of displacements for Variant 4—W\({}_{\text{max}}\) = 3.73 mm.  
Figure 20: Map of displacements for Variant 3—W\({}_{\text{max}}\) = 0.977 mm.  
Table 4 lists the maximum values of displacements and reduced H-M-H stresses of the strength analysis results obtained. The comparison of the maximum values of displacements and reduced H-M-H stresses in individual numerically analyzed variants confirms that Variant 4 is the most strenuous operational case of lifting and loading/unloading the platform with the maximum weight of logs, corresponding to lifting the platform using hook devices.