Investigation of cause of failures of Highway cross drainage Structures (Case study on Raya River Bridge)
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Date
2010-07
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Addis Ababa University
Abstract
Bridges that cross the rivers and valleys are vital components of the road network that contributes greatly to the national development and public daily life. Any damage or collapse of bridge can risk the lives of road users as well as create serious influence to the entire country. Furthermore, the reconstruction of the bridges needs considerable amount of money and time. In fact, Ethiopia has experienced many cases of bridge collapse and their serious consequence over decades.
The main factors for the failure of the drainage structures are due to basin characteristics, stream channel characteristics, flood plain characteristics and meteorological characteristics; and these factors categorized as hydrologic failure, hydraulic failure, failure due to gradation and failure due to orientation of the Structure. Of these categories of bridge failures the Raya river bridge is categorized in the form of failures due to gradation. Hec- Ras and other supporting software’s were used to analyze the cause of the failure of the Raya river bridge. DEM data, surveying data at the bridge cross section, land use data and other supporting data’s were used to estimate the amount of sediment deposition or long term river bed level rise (aggradation) at the bridge location. The analyses of the data’s shows that there is a clear reduction of flow area or opening size at the bridge location due to long term river bed level rise or aggradations around the bridge crossing location resulted from sediment accumulation around the bridge location. The obtained results shows that the main cause of Raya river bridge failure is due to reduction of flow area or opening size at the bridge location due to deposition of sediment which is estimated about 0.588m depth of deposition each year at the bridge location.
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Keywords
Bridge location, National development