As Hull learns another major road in the city is to close for 6 months, our bridges and culverts correspondent Angus Young plunges into the reasons why.
Celebrated mathematician and philosopher John Venn never actually saw the Hull bridge with its colourful design commemorating his famous diagram of overlapping circles. The current Drypool Bridge opened in 1961 some 38 years after his death. Venn was born in Drypool parish but by the time the original Drypool Bridge (sometimes referred to as Salthouse Road Bridge) opened in 1889 he was working as a lecturer at Cambridge University. His most famous book was called The Logic of Chance in which he championed the frequency theory of probability. He claimed probability should be determined by how often something is to occur as opposed to educated assumptions. Had he been around today, Venn would have almost certainly worked out the high probability of urgent repairs being required sooner rather than later on the structure given a funky makeover in his honour during Hull’s year as the UK City of Culture.
The bridge is expected to close to road traffic for six months in April to allow for repairs to be carried out with the most pressing work likely to centre on a series of rapidly-crumbling concrete support columns under the fixed east span. How the columns came to be in such a bad state still remains something of a mystery.
Bridges in Hull are subject to general inspections every two years. Typically, these involve visual examinations without securing close access. A more thorough principal inspection is carried out on each structure every six to 10 years. In these, inspectors get within touching distance of all elements of the crossing. Bridges that carry traffic are subject to structural reviews every 12 to 20 years. These reviews take into consideration any changes to assessment guidance codes and the condition of the structure to check if there is a need for a full assessment to be made.
However, a series of special inspections were being carried out at Drypool Bridge every six months following concerns over sections of the bridge being unable to maintain its 40-tonne weight limit. Extensive deterioration of the columns had not been picked up as an issue in the previous inspection. Six months later, they were serious enough to trigger an emergency 16-day closure of the bridge.
Why such speed? Two suggested reasons have been put forward. Either the concrete was finally showing its age or the immediate marine environment of salt water and silt and had finally taken its toll. It’s quite possible both factors played a part along with the fact that the structure is now much more encased in silt than it ever was, reflecting the wider build-up of silt and mud in the River Hull in recent years as a result of less river traffic and less dredging. Or someone just missed it six months earlier.
Such is the urgency to maintain the bridge’s 40-tonne weight limit, councillors recently bit the bullet and agreed to the work starting on site as soon as possible instead of waiting any longer. It means the six-month project will clash with the ongoing disruption caused by the National Highways upgrade of the A63, bringing extra headaches for motorists.
Would Venn have approved of all this? Perhaps. Would he have brought along a machine he also designed and built himself to automatically bowl cricket balls and aim it at whoever was responsible? Having previously seen a prototype machine clean bowl an Australian test star four times, I think in all probability he would.