## 4 Discussion
### Calculation of Overturning and Stabilizing Moments
The maximal values of the coefficients are as follows \(C^{1}{}_{Mc}\) = 2.299, \(C^{2}{}_{Mc}\) = 2.212, and \(C^{3}{}_{Mc}\) = 1.920 for configurations 1 st, 2 nd, and 3 rd, respectively. To estimate the wind speed, which could cause the tip over the investigated scissor lift, it is assumed that \(M_{S}<M_{C}\), where \(M_{S}\) is the static moment generated by the self-weight of the structure, Figure 18b. This moment can be computed as follows:  
Figure 13:0  
where \(S\) = 44 kN is the self-weight of the scissor lift (Table 1) and \(r_{1}\) = 2.31 m, according to the technical properties of the scissor lift presented in Figure 13:1 Next, assuming the density of the air is equal to \(\rho\) = 1.225 kg/m\({}^{3}\), the critical wind speed can be determined as:  
Figure 13:2  
where \(A_{ref}\) = 9.996 m\({}^{2}\) and \(h_{ref}\) = 7.25 m for the configuration 1 st, 2 nd and \(h_{ref}\) = 3.625 m for the configuration 3 rd for the real structure. Finally, the critical values of the wind speed for studied variants of the scissor lift are as follows: \(V^{1}{}_{ort}\) = 22.315 m/s (80.337 km/h), \(V^{2}{}_{ort}\) = 22.750 m/s (81.902 km/h), and \(V^{3}{}_{ort}\) = 34.534 m/s (124,322 km/h). The obtained values seem to be relatively high, but the main impact on the critical values of the wind speed possess the presence of the workers on the platform. The estimation of the impact of the presence of human beings on the work platform on the critical wind speed should be considered quite problematic. First, the people who stand on the platform of the scissor lift are not \"permanently installed\" on the floor. Therefore, they can transfer the load induced by wind only when they lean on the guardrails. Moreover, the highest load induced by the silhouette of a man is when the people are positioned facing the wind direction. Besides, people differ from each other in height, silhouette, and  
Figure 13:3 Calculation based on the CFD (**a**) the moment coefficient \(C_{Mc}\) as a function of the wind direction described by angle \(\beta\), (**b**) the schema of the loads acting on the investigated scissor lift. weight. Thus, there are an almost infinite number of possibilities. Therefore, it seems that the most reasonable approach to estimating the impact of the presence of people on the work platform of the scissor lifts on the critical wind speed is to involve the superposition principles. In the available literature, one can find papers where the authors try to determine the drag force acting on the human body induced by wind, for example, [PERSON] et al. [59], [PERSON] et al. [60], [PERSON] [61], or [PERSON] et al. [62]. The authors of the first-mentioned work [59] performed several CFD simulations to estimate the drag force induced by the human body. Calculations are made for a person of medium build, 172 cm tall. The results of their simulations are reprinted in Figure 13:4  
To estimate the impact of the presence of workers on the platform on the value of the critical wind speed, in the first step, the moment \(M_{C}\)1 induced by the wind at the speed of \(V_{0}=20\) m/s acting on the scissor lift is computed. The assumed density of the air is equal to \(\rho=1.225\) kg/m\({}^{3}\). Next, the moment \(M_{W}\) generated by a single worker of the approximate weight \(G_{W}=800\) N is evaluated, namely \(M_{W}=F_{W}\,h_{2}\), where \(F_{W}\) is the drag force, whose value can be found in Table 8 for the wind speed V\({}_{0}\) (frontal position), and the \(h_{1}=12.5\) m is the distance between the ground and the top guardrail level for configuration 1 st, 2 nd and \(h_{1}=7.25\) m for configuration 3 rd. Finally, the total moment M\({}_{C}\) induced by the wind blowing with a speed equal to V\({}_{0}\) can be computed with the use of the following formula:  
Footnote 1: The critical value of the wind speed \(V_{CRT}\) [m/s]. Figure 13:5  
where \(n_{w}\) is the number of workers on the platform. According to [51], the reference area of the human body is equal to about 0.555 m\({}^{2}\). Therefore, it can be neglected.