Historical ach bridges under horizontal debris flow impact

Alpine regions exhibit based on their topography in comparison to other geographical regions a higher tunnel and bridge density. Historical masonry stone arch bridges form a major part of this bridge stock. Such historical arch bridges have shown an excellent load bearing behaviour despite a dramatic increase of loads. However an even further increase will be limited, since these historical bridges have not been designed for such loads. The increase of loads is not only related to common vertical live load, but also to horizontal accidental loads perpendicular to the longitudinal direction of the superstructure such as ship impacts or debris flow impacts. Failures of bridges under these loads in recent years have shown the significance of this problem. Since historical masonry arch bridges are built since more than 2000 years, there exist a great variety of models to estimate the load bearing behaviour of such structures. Simplest models were based on geometrical rules. Nowadays mainly beam models are used in praxis whereas in research finite-element-models and discrete- element-models have been applied successful in the last decades. A comparable development can be seen in the estimation of impact forces by debris flows. Here also in the beginning simple empirical relationships were applied but in the last years discrete-elements have also been applied. The goal of this research project is the combination of both, the modelling of the arch bridge as well as the modelling of the debris flow impact against the bridge by discrete-element-models. However these models will be supported by dynamic finite element models. The goal of the investigation is an improvement of the understanding of the behaviour of the superstructure of an historical arch bridge under a horizontal impact yielding to simpler engineering models which can be applied under practical conditions.

Historical stone arch bridges are a major part of the Austrian road and railway infrastructure system. Since bridges are usually densely located in Mountain areas, they are also more exposed to Mountain hazards than other structures. One of such hazards are debris flows. Since historical arch bridges are not designed against debris flows, this FWF project had the goal todevelop an understanding of the impact forces created by debris flows on arch bridgesdevelop an understanding of the reaction of the arch bridge exposed to such impacts.During the FWF project miniaturized debris flow impact tests have been carried out in a laboratory of the University of Natural Resources and Life Sciences, Vienna. The test program included the development of a characteristic debris flow mixture, the development of a new force measurement device and the development of a new approach to estimate the impact force of the debris flow based on the miniaturized tests.In the second step, a miniaturized arch bridge has been built and tested in a laboratory of the University of Natural Resources and Life Sciences, Vienna. Since the model was based on an existing arch bridge, deformation measurements from the real-size bridge under vertical load were used to verify the miniaturized arch bridge model. The bridge model was exposed to vertical and horizontal loads. The horizontal loads were either applied in a static way or in a dynamic way. There are no other experiments with horizontal impact loads on arch bridges worldwide known. A finite element program was also used to estimate the force flow inside the arch bridge, based on the deformation measurements on the model.