Engineers have cautioned against figures published by the RAC Foundation which show that almost 200 post-tension bridges managed by local authorities in the UK have not had a specialist inspection in 18 years.
According to the RAC report published today, there are 605 post-tensioned bridges in the UK under the management of 106 local authorities.
Of these, the RAC has determined 199 structures have not had a Post Tensioned Special Inspection (PTSI) in the last 18 years, despite concerns following the collapse of Italy’s Polcevera viaduct last summer. At the time of the collapse, Highways England reassured the public saying no bridges on the UK’s strategic road network bear similarities to that of the collapsed structure in Italy.
While none of the post-tensioned structures in the UK are directly technically comparable with Polcevera Viaduct which collapsed in Genoa in August 2018, the lack of inspections is still a “serious issue” said RAC.
PTSIs are supposed to be carried out every seven years, but the intrusive testing means each one can cost around £100,000. The total cost to fund all the overdue PTSIs could be as much as £21M, the RAC claimed.
The survey of local highways authorities was carried out by the RAC Foundation with the National Bridges Group of Adept (the Association of Directors of Environment, Economics, Planning and Transportation).
Adept National Bridges Group chair Kevin Dentith said a lack of funding and expertise is contributing to the lack of inspections for post-tensioned bridges.
“Bridge maintenance is about priority. In large rural counties, like my own authority, Devon, there will be structures that on paper fall short of current design standards, however they are never likely to be strengthened because they carry little more traffic than the odd car and tractor,” he said.
“However, there is a serious issue around so-called post-tensioned bridges. Whilst these are not directly comparable in technical terms to the bridge that collapsed in Genoa they do require intrusive examination, something many of them will never have had because of a lack of funding, expertise or both.”
Dr Chris Atkins, chair of the Concrete Bridge Development Group, said that these post-tensioned bridges will have undergone risk assessments. He said that the PTSI bridge regime was introduced after a bridge collapse in Wales in the 1970s. At the time there were post-tensioned bridges where it was not known whether the tendons had been grouted, how well they had been grouted and whether they were corroding, therefore there was a significant amount of unknown risk. However, these bridges were dealt with long ago, and now the number of bridges potentially requiring a PTSI is extremely small - he said his team at Mott MacDonald came across one or two of such tenders per year.
“We’ve picked up all the ones that were at significant risk, that people knew nothing about, now it is just flicking through the leftovers,” he said.
Atkins suggested that the 199 post-tensioned bridges that had not had an inspection for 18 years would have had a risk assessment, for example examining whether tendons were at risk of corrosion. He added that now there were proper records on tendon grouting, which also eliminated the need in some circumstances for PTSIs.
Pictured is Transport for London’s Hammersmith Flyoverwhich underwent a successful strengthening programme in 2016.
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