"However, during redecking work in June 1976, a change was made that imposed a weight limit on the bridge, which remains in effect to this day. For reasons that have been lost to time, the central girder under the three arches was reduced in height by approximately 15cm and lifted slightly to ensure boats could pass under the bridge without hitting it."
"The problem is that a smaller girder isn't as strong as a bigger one, that's imposed a weight limit on the bridge ever since. A smaller central girder also increased the load on the surrounding structure, thereby increasing fatigue on the other girders and plates. It's not a problem that affects passengers, but it does mean some freight trains have to avoid the bridge, as do the heavier Network Rail engineering trains."
"However, as the engineers from VolkerFitzpatrick realised, the Chiswick and Hammersmith road bridges on either side of the railway bridge are both lower, so there's no way a taller boat could have got past them to hit the Barnes bridge anyway. The reason engineers were examining the bridge is twofold. Firstly, it was approaching its 50-year maintenance lifespan, but there was also an urgency to repair some of the securing pins that held the bridge crossspans together, as they had been damaged by vibration."
Barnes railway bridge reopened to passengers after maintenance work resolved a structural issue dating from 1976. The site comprises two adjacent bridges: a disused 1849 cast-iron original and an 1890s wrought-iron replacement with three bowstring-girder spans. During redecking in June 1976 the central girder was reduced in height by roughly 15cm to allow river traffic, which weakened the span and imposed a weight limit that persisted. The smaller girder increased load and fatigue on surrounding members, restricting freight and heavy engineering trains. Engineers repaired damaged securing pins and removed a speed restriction, enabling passenger services to resume.
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