|
Problems connected with the application of lamella flanges in steel bridge construction
Křístek, V. ; Kunrt, J. ; Škaloud, Miroslav ; Urushadze, Shota
Lamella flanges have lately grown very popular with the designers of steel bridges, because - in their belief - they provide us with the possibility of avoiding very thick flange plates in steel bridge structures. This belief is based on the assumption that the lamellas are perfectly plane and therefore, in perfect contact everywhere, so that the loading from one lamela is transmitted into other via pure compression, and that the perfect interaction of both lamellas is materialized by means of boundary fillet welds connecting both of the two lamellas. This simple assumption is, however, far from reality: it is not the means of steel fabricators, not even in the means of those which are very progressively equipped, to produce perfectly plane lamellas. Then both lamellass exhibit unavoidable initial curvatures, which in combination form a gap between the lamellas, and consequently the directly loaded lamela are pressed into this gap. As the loading acting on every bridge is many times repeated, the aforsaid phenomenon is also many times repeated, (we can say that the lamellas "breathe"), and then an unavoidable cumulative damage proces in the lamellas comes to being. The results of investigation will be described in the paper and thereby will demonstrate that the fatigue phenomenon accompanying the breathing of the lamellas can considerably limit the lifetime of the structure.
|
|
The "miracle" of post-buckled behaviour in thin-walled steel construction and some limitations to its full exploitation
Škaloud, Miroslav ; Zörnerová, Marie
Thin-walled steel structures, i.e. structural systems made of thin (usually plate) elements, represent a powerful tool for increasing the competitiveness of steel construction. Then, on the other side, it is in the nature of things that the limit state of the systém is in the danger of being substantially reduced by stability phenomena. Fortunately, the situation is remedied by the beneficial effect of post-buckled (post-critical) behaviour, which is in detail described and "mapped" in the contribution. However, attention is also turned to some limitations which in some cases hinder a full exploitation of the phenomenon, one of them, viz. the unavoidable reduction of the post-buckled reserve of strength due to breathing-induced fatigue, being described in detail in the paper
|