TRIPPING OF ASYMMETRICAL STIFFENERS UNDER COMBINED LOADING Final Report by Alexis Ostapenko

Presented is a study of the tripping strength of asymmetrical longitudinal plate stiffeners subjected to a combination of axial and lateral loads. The loaded edges were taken to be simply supported. The method of analysis is based on the principle of minimum total potential, and ten displacement functions were used to describe the deformations of the plate and stiffeners. First yielding was used as the criterion of ultimate strength. Instability under axial loading was investigated for the symmetrical (Tee) and asymmetrical (Angle) stiffeners. Angle stiffeners showed greater capacity than Tee stiffeners for lo\ver values of the slenderness ratio (L/r), but lower capacity for higher values of the slenderness ratio, especially, after consideration of the deformations of the stiffener web. Under combined axial and lateral loads, there was a significant decrease in the capacity for asymmetrical (Angle) stiffeners due to the distortion bf the cross section as compared to the undeformed or symmetrical sections. A modified effective width concept was introduced into the analysis to consider the effect of postbuckling plate deformations under combined loading condition. The effect of initial imperfections of stiffeners was also included. A relationship for the interaction between the axial and lateral loads was established for the ultimate condition. It shO\\T8 that the ultimate strength can actually increase under axial loading when the lateral loading is applied in the direction from plate to stiffener. When the lateral loading is applied in the other direction, the interaction is almost linear. The computer program developed during the study \vas the main tool to provid.e the needed numerical results.