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Hidden Defects in Bridges
25th April 2017 @ 6:00 pm - 8:00 pm
Amrit Ghose, formerly of AECOM, is heading a team who are producing a CIRIA report on hidden defects in bridges. During this talk, he will explain that the core component of a bridge management programme is on-site examinations by a competent bridge inspector. These inspections are central to recording bridge condition, used by bridge owners to ensure defects are identified and rectified within reasonable timeframes as well as identifying larger maintenance works.
In general, this works well in the UK and Ireland: bridge stock is generally safe for use with the aim of being fit for purpose. However, the process is based wholly on the quality of the inspections. If an inspection does not include all elements since, for example they are hidden and not easily examinable, the adverse effects can be significant or, in the worst cases catastrophic.
Two high profile cases in recent years have bought the importance of defects in hidden bridge components to centre of bridge owners’ focus. In 2009, the Stewarton rail bridge, Ayrshire collapsed during passage of a freight train. Corrosion to half-through girder webs was so severe that complete loss of section had occurred in areas of high shear load. The corroded areas were hidden under ballast and had not been inspected. The M4 Hammersmith flyover, London had an inspection of hidden post-tensioning cables undertaken in 2011. Condition was so poor that an emergency closure and strengthening works were undertaken to restore highway traffic on one of London’s busiest roads. Prompted by these cases, bridge owners in UK and Ireland identified the need to define good practice when inspecting, identifying and maintaining hidden bridge components. The forthcoming CIRIA report will establish this as well as providing guidance on how to avoid creating potential for such defects in design.