# Analysis of Selected Methods of Computer-Aided Design for Stage Structures
## 3 Testing and Analysis of the Load-Bearing Structure of a  
### Semic Trapdoor  
The third stage during the design of the supporting structure was the calculation of the main elements of the designed structure [17, 18, 19, 20, 21] and analysis using the Soldis PROJEKTANT program for the calculation of supporting structures. Loads results from the operating characteristics of the stage trapdoor were applied. The loads that occurred were calculated according to \"DIN 56950:2005-04-Technique for stage performances--Technical machinery and equipment--Safety requirements and tests\" [22]. In Autodesk Inventor, a 10 mm square mesh with second-order parabolic elements was used, providing higher accuracy in stress concentration areas, with default convergence settings. In geometric locations that were more difficult, triangular elements were used, with the possibility of adaptive mesh refinement. In the analysis of the structure in the Soldis Designer environment, assumptions of the classical Euler-Bernoulli beam theory were adopted, neglecting torsion effects. Autodesk Inventor 2022 is equipped with a module for the analysis and testing of frame structures (Figures 4 and 5), which was used to verify calculations carried out in the Soldis PROJEKTANT program. This module also enabled the analysis of the behavior of the structure under increased load. Thanks to its functionality, which takes into account the spatial 3D model (Figure 6), Autodesk Inventor 2022 allowed a more detailed examination of the modeled structure. In contrast, Soldis PROJEKTANT analyzed the structure in a flat 2D model. The examination took into account the actual support model of the supporting structure [23, 24, 25]. Figure 3: Diagram of the supporting structure—section A-A—upper platform: 1—upper stringer, 2—lower stringer, 3—supporting column, 4—column mounting (SERAPID), 5—guide mounting. Figure 4: Screenshot of upper longitudinal member deflection arrow. Figure 5: Screenshot displaying stresses diagram at highest and lowest points. Figure 6: Screenshot presenting 3D model of designed stage trapdoor. The conducted study precisely indicated the locations of the greatest displacements in the supporting structure (Figure 7). Differences in the calculated displacements may have resulted from the use of a complex 3D model of the entire structure. The favorable deflection values of the upper longitudinal members were influenced by the presence of intermediate frames, which increased the stiffness of the analyzed structure. The occurring stresses did not exceed the yield strength for S235 steel. Therefore, under the analyzed structural operating conditions, the use of S355 steel was not necessary. In order to thoroughly analyze the steel structure, tests were carried out for four load cases with different values ranging from 9.81 kN (1000 kg) to 147.1 kN (15,000 kg). These cases corresponded to the most commonly occurring loads on stage structures and the most realistic operating conditions to which they may be subjected. The first type of load was a constant load with a constant value q acting evenly over the entire length of the structure. In the second case, the frame was also loaded along its entire length, but the value of q increased every 2500 mm according to the formula described later in this article. The third type of load was characterized by three q values, arranged in such a way that the highest value occurred at the central point of the structure. In the fourth case, the highest loads were located at the outer edges of the structure, and the lowest in its central part. Load distributions for all cases are shown in the illustration below (Figure 8).