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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Flood risk management and adaptation : Stability of short-span bridges subject to overtopping during floods: case studies from uk/ireland a...
Stability of short-span bridges subject to overtopping during floods: case studies from uk/ireland and the usa
Author : DONAL RYAN1, ROBERT ETTEMA2 ,BRIAN SOLAN3, GERARD HAMILL4 JOHN MCROBERT5
ABSTRACT
As a consequence of increased levels of flooding, largely attributable to urbanization of watersheds (and perhaps climate
change, more frequent extreme rainfall events are occurring and threatening existing critical infrastructure. Many of which
are short-span bridges over relatively small waterways (e.g., small rivers, streams and canals). Whilst these short-span
bridges were designed, often many years ago, to pass relatively minor the then standard return-period floods, in recent times
the failure incidence of such short-span bridges has been noticeably increasing. This is suggestive of insufficient hydraulic
capacity or alternative failure mechanism not envisaged at the time of design e.g. foundation scour or undermining. This
paper presents, and draws lessons, from bridge failures in Ireland and the USA. For example, in November 2009, the UK
and Ireland were subjected to extraordinarily severe weather conditions for several days. The resulting flooding led to the
collapse of three UK bridges that were generally 19th century masonry arch bridges, with relatively shallow foundations.
Parallel failure events have been observed in the USA. To date, knowledge of the combined effect of waterway erosion,
bridge submergence, and geotechnical collapse has not been adequately studied. Recent research carried out considered
the hydraulic analysis of short span bridges under flood conditions, but no consideration was given towards the likely damage
to these structures due to erosive coupling of hydraulic and geotechnical factors. Some work has been done to predict the
discharge downstream of an inundated arch, focusing on predicting afflux, as opposed to bridge scour, under both
pressurized and free-surface flows, but no predictive equation for scour under pressurized conditions was ever considered.
The case studies this paper presents will be augmented by the initial findings from the laboratory experiments investigating
the effects of surcharged flow and subsequent scour within the vicinity of single span arch bridges. Velocities profiles will be
shown within the vicinity of the arch, in addition to the depth of consequent scour, for a series of flows and model spans.
The data will be presented and correlated to the most recent predictive equations for submerged contraction and abutment
scour. The accuracy of these equations is examined, and the findings used as a basis for developing further studies in
relation to short span bridges.
File Size : 1,642,431 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Flood risk management and adaptation
Date Published : 14/08/2015
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