Abstract

Stiffened cylinder is widely used in launch vehicle structures because its stiffener can prevent buckling wave to spread in the skin. However, it is still sensitive to shape imperfection more or less. Knockdown factors of stiffened cylinders have been researched all the time. However, comparison among different grid types is seldom. In this paper, both orthogrid stiffened cylinder and isogrid stiffened cylinder under axial compression are studied. Linear eigenvalue method and nonlinear implicit method are adopted to calculate the bearing capacities of the cylinders with ABAQUS. The sinusoidal function is used to model the imperfection. Given different imperfection parameters, the sensitive of bearing capacities to the shape imperfection is researched for two kinds of cylinders. Axial compression experiments are also implemented for the stiffened cylinders, and the results agree with numerical result. Knockdown factor of orthogrid cylinder is about 0.5~0.7. Meanwhile, it proves that when the stiffener is strong enough, the effects of shape imperfection on load capacity can be ignored for orthotropic grid, and its knockdown factor is nearly 1.

Abstract

Fitness-for-purpose (FFP) assessment is used for estimation the durability of welded plate girders in Poland’s four oldest welded railway bridges. For the girders, the 20.2 m span length was designed. The bridges were constructed over the years 1937-1939 and now being readied for refurbishment. The first radiographic tests on the butt welds in 18 bridge plate girders were conducted in 1958 during which 101 internal cracks in 49 butt weld splices were found, and which were subsequently riveted. The usefulness of such a strengthening is assessed upon structural calculations for design and service loadings, fatigue tests on specimens with internal cracks in the welds, literature service strength of welds with cracks and design fatigue strength of welds with cracks using FFP assessment. The results provide a unique experimental database on the behavior of welds with inadmissible imperfections. They also allow to assess the likely length of their further service life.