Out-of-plane buckling curve for steel tied arch bridges

The behavior of steel tied arches consists of the fact that a large compressive force is developed. Steel arches in particular are highly sensitive to out-of-plane buckling. There is no clear and generally accepted method to numerically predict this stability problem. On one hand, the buckling strength of an arch bridge can be calculated by considering non-linear elastic-plastic behavior. As the imperfections of the arches highly influence this non-linear behavior, the former need to be known prior to the analysis. On the other hand, a linear stability calculation, resulting in an elastic buckling factor for the compression force, can be carried out. From this a multiplication factor for stresses can be derived, using a specific buckling curve. To choose the adequate buckling curve, the arch imperfections should be known. The imperfections of an arch in a slender steel arch bridge are not related to those of a straight beam which makes it quite impossible to use standard buckling curves, derived for straight beams. To improve the knowledge on this part, a finite element model was developed of a steel tied arch bridge. The model has been used to obtain a buckling curve for arch bridges based on elastic-plastic calculation of the actual buckling behavior. This buckling curve is also based on the effect of theoretical geometrical imperfections, consisting of curves with a single sinusoidal arc, similar to the current buckling curves for straight beams. The use of a specific buckling curve for arches should optimize the buckling design of arch bridges quite substantially.