Aspects of thin-walled structural behaviour

It is believed that thin-walled structures have an important role to play in development of new concepts of structural systems. It is, therefore, important to understand the behaviour of these structures and to express this understanding in a form of changes and development of design rules. Aspect ratio is one of the main parameters which influences the behaviour of thin-walled structures. The study herein recognises the influence of aspect ratio on different types of thin-walled structural behaviour. It is shown that a simply supported box girder experiences transverse membrane stresses along the centre-line of the flanges. These stresses are sensitive to the flange aspect ratio. An idea due to Heyman is presented which assumes a box-section to be the assembly of two channels built-up toe-to-toe. A concentrated load, which acts on the web/flange junction, introduces a twisting effect. In order to keep the box in the no-twist-position a lateral force is needed. Based on this idea and a parametric finite element study, two simple empirical equations are introduced. The equations predict the magnitude and the distribution of transverse membrane stresses along the centre-line of the flange. These stresses, in some cases, have a value which is several times the value of the associated longitudinal stresses. The same argument is used to evaluate the transverse membrane stresses in I-beams which are regarded as being assembled by placing two channels back-to-back. Simple equations are again presented to predict these stresses. The study is extended to investigate the influence of the aspect ratio on the bending lag phenomenon in the compressive flanges of box girders. When elastic buckling of the flange is assumed negative bending lag is detected. The study also covers the influence of the aspect ratio on the behaviour of profiled sheets when subjected to concentrated loads causing flexure. The results show that local plastic failure occurs initially in shorter spans rather than longer spans when the profile height is shallow. These anomalous results are evaluated and recommendations are given in view of the evaluations. It has been the aim to provide a physical understanding of the structural behaviour in addition to the evaluation of stresses and deformation in the various cases studied