Maarten De Strycker

Stringer Stiffened Cylinders on Local Supports – The Plastic Buckling Behavior

The buckling behavior of locally supported cylinders is a topic that is still the subject of many investigations. Adequate design rules have yet to be incorporated into the codes. In this contribution, the plastic buckling behavior of a stiffened cylinder on local supports is studied. Our research consists of two principal components, i.e. experiments on scale models and numerical simulations. Here the numerical simulations are discussed. Firstly the effect of the yield stress is investigated. In order to find a design rule, a large parametrical study has to be performed. In this contribution, the characteristics and the results of this study are described. The simulations show that for a radius to thickness ratio of the cylinder equal to 250, the optimal stiffener dimensions correspond with a plastic buckling phenomenon and a failure stress that is larger than the yield stress. For larger values of the ratio, the elastic instability of the stiffeners precedes the plastic buckling and this shows that the stiffener configuration is not suitable for these values of the radius to thickness ratio.

Residual Stresses in TIG-Welded I-Beams. Experimental Test-Setup and Validation of Numerical Model

The presence of residual stresses is a determining factor in the buckling behaviour of steel beams. It is therefore necessary to know the magnitude and the distribution of residual stresses in welded beams. Experimental measurements of these residual stresses are expensive, timeconsuming and they give no insight in the evolution of the stresses during the welding process. For these reasons it is interesting to have a numerical model which allows a prediction of the residual stresses due to welding and which allows a study of the parameters that have an influence on the residual stresses (e.g. yield stress, heat-input, thermal expansion coefficient, …). Such a numerical model can result in a proposal for a welding process that leads to less detrimental residual stress distributions in welded I-beams. However, the results of the numerical model must always be checked with reality. This contribution contains the experimental verification of the finite element model for both single plates and I-beams with rather small dimensions. First, an overview of generally accepted influencing factors on the residual stresses is given. After this introduction, a setup which allows control of the parameters for making reproducible weld seams is presented. This setup is usable for both plates and I-beams. Next it is described how the residual stresses in a plate and a beam were measured. Finally the results obtained from different configurations in the experiments are compared with the results from the FE-model. It is shown that the FE-model gives reliable predictions for the residual stresses.