Issue 48

E. Maiorana, Frattura ed Integrità Strutturale, 48 (2019) 459-472; DOI: 10.3221/IGF-ESIS.48.44 469 Fig. 9 shows the relationship between the optimum value of stiffener position h  / h and stress gradient  for the four groups. When   0, all the curves have enough h  / h points in common; when  < 0 , the positions of points h  / h could be measured in each case. This is explained by the fact that, for   0 , compression dominates bending, whereas for  < 0 , bending dominates compression. In the latter case, stress distributions change in subpanels h  and h  ; accordingly, the optimal position differs in each load condition. Increasing the value of  in the zone of positive abscissa, the optimal stiffener position moves toward the center-line of the plate, giving h  / h = 0.5 in the case of pure compression stress,  = -1 . (I) (II) (III) (IV) Figure 8: Plate a = 3 m, h = 1.5 m and t = 20 mm. Out-of-plane displacements  z from 1 st buckling mode. Figure 9: Optimum value of stiffener position h  / h vs. stress gradient  . Looking at Fig. 8, groups OF1-I and OF1-II show marked deformation of the stiffener after the half-waves produced in the plate plan, reaching critical load; they were therefore classified as flexible types. Group OF1-IV shows a clear distinction 0.10 0.20 0.30 0.40 0.50 -1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1  h' / h I II III IV -1 -0.75 -0.5 - .2 . 1