With the RAC Foundation reporting on the number of UK road bridges deemed 'substandard', Professor Wanda Lewis, a structural engineer from the School of Engineering at the University of Warwick, discusses the challenges in improving the condition of these bridges.
Professor Lewis said: "There have been comprehensive reports published by the RAC Foundation, year on year, about the alarming state of bridges under local authority control; these reports are based on surveys of over 200 local authorities. The 2019 report states that the highest number of substandard bridges is found in: Devon, Essex, Somerset, and Cornwall. Up north , the most affected areas are: Aberdeenshire, Perth and Kinross, East Ayrshire, and Highland, while in Wales: Conwy, Powys, and Carmarthenshire top the list. The latest cost estimate has gone down from £6.7 billion a year ago to £5.5 billion, and the number of substandard bridges from 3194 to 3061, according to the report just published.
"The backlog of bridges needing repair or replacement continues to grow. Cuts to the local authorities budgets, which are now also given social care provision as a priority, are one of the reasons for the situation; skills shortages, and attitude to maintenance, are another.
"There is a growing concern amongst the civil engineering community about the impact of climate change on buildings, bridges and roads infrastructure. The codes of practice to which engineers design, do not consider very high winds, temperature variations, or severe flooding, as frequently occurring loads; this is now being reviewed , as it affects the outcome of the design solutions. Concrete used to be viewed as an ‘everlasting’ material but, as is appreciated now, it is subjected to continual chemical attacks from the atmosphere, temperature changes, and moisture variations, all of which reduce its durability. Flooding is responsible for scouring of bridges and this calls for more robust designs to be produced in the future.
"Most bridges are simply too old, approaching their design lifespan. Ancient masonry bridges (many of which exceeded the currently expected lifespan of 120 years) are crumbling all over the country, as reported by Bill Harvey – an expert on masonry bridge analysis and maintenance. More modern bridges that are of great concern are the pre-tensioned concrete structures, in which steel is placed inside concrete and tensioned; when concrete (intended to provide protection for the steel that is 10 times stronger) deteriorates, it affects the steel and can lead to catastrophic failures.
"In recent years, monitoring and assessment of bridges have led to load restrictions put on them. This impacts our transport network and economy. Bridge assessments are usually carried out using cheap techniques, such as visual inspections, rather than the more expensive techniques involving infra-red imaging, or samples of material taken from the structure for testing. While visual inspections bring useful information, they cannot fully assess the extent of the damage.
"Current government’s priority regarding our infra-structure focuses on central communication networks, but it is the health of our local infrastructure/ bridges that requires urgent attention and funding."
28 February 2020
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