PRACTICAL APPLICATIONS FOR CONSTRUCTION AND THE BUILT ENVIRONMENT
Innovation & Research
Issue No. 93 IN THIS ISSUE
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Also at www.innovationandresearchfocus.org.uk
May 2013 Assessing scour risk on bridges
Despite the undesirable consequences associated with structural failures at river crossings, it is rare that suffi cient funds are made available to undertake all necessary improvement acti viti es. It is in the face of limited budgets that diffi cult decisions must be taken in order to decide how and where limited resources should be invested and, conversely, where interventi on is not fi nancially justi fi ed. Understanding risks along transport networks is fundamental to their operati on and provides an evidence base to defi ne management acti ons and strategies.
esearchers at HR Wallingford have developed a new framework and method to develop a probabilistic scour risk assessment. This will contribute to assessing, in a quantitative and analytically rigorous way, the risks of scour failure at bridges. As a result, decision makers will be able to have greater confi dence in the risk assessments on which they are basing their infrastructure investment decisions. The work has been developed under the FUTURENET project, funded by the Engineering and Physical Sciences Research Council and part of the Adaptation and Resilience to Climate Change Programme. The research project addresses the issue of identifying vulnerabilities in transport infrastructure to climate change. The London-Glasgow transport corridor (including highways and railways) is being used as the focus of the project. Climate change is putting a renewed focus on assessing the likelihood of failure of key structures such as bridges. Examples of recent bridge failures in Europe are: • the large number of bridges destroyed during the Cumbria fl oods in 2009 in UK – causing loss of life and extensive traffi c disruption;
• the Margarola bridge in Spain that failed in 2006 due to the interaction with the scour at a nearby bridge – causing two casualties; and
• the Hintze Ribeiro bridge in Castelo de Paiva in Portugal, which collapsed in 2001 due to general degradation of the river bed because of dredging – causing 60 casualties.
The new methodology uses fragility curves to account for uncertainty as well as taking into account the protection around bridges. The presence of protection works aims to change the relation between scour and the probability of failure of the infrastructure, as protection “delays” the possible exposure of bridge foundations by controlling the channel position and increasing the
Failed bridge due to scour (source: HR Wallingford).
hydraulic load needed to fail the protection. The methodology developed to estimate the probability of bridge failure due to scour at river crossings aims to be repeatable, as much as possible, independently of the user, and easy to update as more information or better knowledge becomes available. It is not aimed at estimating the risk associated with a particular event; instead, it is aimed at estimating all possible events in order to obtain an annual probability at each bridge site. The annual probabilities calculated for different climate change scenarios can then be compared to chosen thresholds of safety levels to establish the necessary management strategies.
For further information please contact Dr Marta Roca Collel, Engineer HR Wallingford
(01491 823303; E-mail: m.ro
ca@ hrwallingford. com).
FUTURENET has been developing quantitative methods for the evaluation of resilience to extreme weather events and climate change in the UK transport network.
Innovation & Research Focus Issue 93 MAY 2013
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