Wood accumulation at bridges exerts additional forces to the structures and aggravates local scouring around piers, which may result to bridge failure. Moreover, it may considerably reduce the flow opening causing higher flow levels and inundation of nearby areas. On the other hand, the important ecological role of instream wood in fluvial systems calls for a compromise between preservation of river ecosystems and prevention of instream wood-related hazards. The present PhD research aims to enhance the knowledge on the process of interaction between wood and bridge piers. The two main objectives were first to find the wood accumulation probability (here called "blockage probability") as a function of the bridge pier geometry (with a focus on non-standard pier shapes typical of historical cities), hydraulic conditions of the approaching flow, and wood transport regime, second to assess the capability of 2D and 3D numerical models in reproducing the interaction between wood and structures (i.e. the bridge pier). The combined experimental and numerical research approach is used. The results showed that blockage probability at the flatter pier shape is three times greater than the triangular shaped piers, in congested wood transport regime and at high Froude number (in this case Fr=0.5). In case of Ogival pier, zero blockage probability was found for both cases of Froude numbers. Potential flow analysis indicated that the lower curvature of the streamlines at the rounded pier favours the log sliding the pier. Despite the capability of the 2D model in reproducing the log transport, the discrepancy between experimental and the 2D numerical results showed the inability of modelling the important secondary flows and the log-pier interactions. Furthermore, the 3D modelling allowed to reproduce the 3D character of the wood-pier interaction process as the logs that move along the vertical upstream face of the pier, the non-elastic collision between logs and between logs and the pier, and the skin friction of logs. Finally, ...
Experimental and numerical investigations on wood accumulation at bridge piers with different shapes ; Experimentelle und numerische Erforschung der Holzansammlung an unterschiedlichen Brückenpfeilerformen
20.02.2018
Hochschulschrift
Elektronische Ressource
Englisch
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