## 3 Results and Discussion
### Geometric Evaluation
#### 3.3.2 Influence of \(P_{z}\) and \(h_{s}/t_{s}\) over \(\sigma_{uN}\)  
Two distinct behaviors from the influence of \(P_{z}\) and \(h_{s}/t_{s}\) over \(\sigma_{uN}\) were identified in this study: in stiffened plates having \(N_{ls}\) < 4 (represented in Figure 17 by stiffened plates \(N_{ls}\) = 2) and those with \(N_{ls}\) \(\geq\) 4 (represented by stiffened plates with \(N_{ls}\) = 4, which will be presented and discussed later). In stiffened plates with \(N_{ls}\) < 4, from Figure 17, it can be noted that the application of positive lateral pressure reduced the \(\sigma_{uN}\), while negative lateral pressure increased \(\sigma_{uN}\). For positive pressure, lower values of \(h_{s}/t_{s}\) resulted in a severe reduction in \(\sigma_{uN}\). This can be explained by the displacement resulting from the application of positive lateral pressure and subsequent biaxial loading, as illustrated in Figure 18.  
In plate configurations with \(N_{ls}\) < 4, one can observe in Figure 18 that lower values of \(h_{s}/t_{s}\) resulted directly in a global displacements distribution (Figure 18a), and the subsequent application of the biaxial loading maintained this mechanical behavior (Figure 18b), increasing the out-of-plane displacements and leading to a quick structural collapse. On the other hand, higher values of \(h_{s}/t_{s}\) resulted in local displacements distribution due to the application of lateral pressure (Figure 18c). With the subsequent application of biaxial loading, the displacements just evolved until the local collapse of the stiffened plate (Figure 18d). So, in the graphics on Figure 17, at the values of \(h_{s}/t_{s}\) the \(\sigma_{uN}\) increased, and the stiffened plates geometry results into local displacements until collapse. Figure 16: Unstiffened plate with application of \(P_{z}\) = 0.16 MPa: (**a**) \(U_{z}\) due lateral pressure, (**b**) \(U_{z}\) due application of lateral pressure and biaxial compression, and (**c**) von Mises stress distribution due application of lateral pressure and biaxial compression. Also, for plates configurations with \(N_{ls}<4\), the negative pressure improved \(\sigma_{uN}\). It can be explained by the displacement resulting from negative lateral pressure and subsequent biaxial loading, shown in Figure 19, in which lower values of \(h_{s}/t_{s}\) resulted in global displacements distribution due to the application of lateral pressure (Figure 19a), and subsequent application of biaxial loading overcame these displacements, resulting in local displacements until collapse (Figure 19b). Higher values of \(h_{s}/t_{s}\) resulted in local displacements due to the application of lateral pressure (Figure 19c), and the subsequent application of biaxial loading also overcame these displacements until the local collapse (Figure 19d). From this reason, there is no significant variation on \(\sigma_{uN}\) in the graphics in the figures. Figure 17: Influence of \(h_{s}/t_{s}\) and lateral pressure \(P_{z}\) on \(\sigma_{uN}\) in plates with \(N_{ls}<4\): (**a**) P(2;2), (**b**) P(2;3), (**c**) P(2;4), and (**d**) P(2;5). Figure 18: Influence of \(h_{s}/t_{s}\), positive lateral pressure, and subsequent biaxial compressive loading on displacements of plates with \(N_{ls}<4\): (**a**) \(h_{s}/t_{s}=1.02\) and lateral pressure, (**b**) \(h_{s}/t_{s}=1.02\), lateral pressure, and biaxial loading, (**c**) \(h_{s}/t_{s}=20.13\) and lateral pressure, and (**d**) \(h_{s}/t_{s}=20.13\), lateral pressure, and biaxial loading. Figure 17, indicating that all \(h_{s}/t_{s}\) values led to local displacements due to the application of biaxial compressive loading until local collapse. In turn, the results for the stiffened plates with \(N_{ls}\geq 4\) is presented in Figure 20, represented by the cases with \(N_{ls}=4\).