Analysis of the forms of the loss of stability of ribbed shells

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1. An increase in the number of ribs in the stringer-reinforced shells may result in the change from one isolated form of stability loss to another in accordance with the conditions n=ks, n=ks/2, n=ks/4, etc.; at the instant of transition from one form to another, the total critical load may decrease with an increase in the number of ribs. 2. The data obtained on the basis of multiterm approximation are similar mainly to the results corresponding to single-term approximation for the even number of ribs, and also to the intermediate numbers of ribs. It is thus possible to propose a correction for the data obtained on the basis of single-term approximation for the odd number of ribs using the intermediate values of the critical loads between the adjacent even numbers of ribs. 3. The effect of the torsional stiffness of the ribs (even for Icrs/t4>Is/t4) on the critical load in the majority of cases is small and equals 22% only in a single case of all the examined cases; the magnitude of this effect will decrease even further with the reduction of torsional stiffness. 4. The critical loads determined on the basis of multiterm approximation may decrease by 18% (e. g., for 20 stringers) in comparison with the data obtained for single-term approximation.