21 November 2024 – Railway Bridge Disasters and Mishaps by Alan Hayward, Civil Engineer
Alan is a well qualified practicing civil engineer and we were delighted to welcome him for a full length presentation at the Branch having been impressed with a short impromptu talk on a previous occasion when the booked speaker was running very late. He listed a number of incidents to be covered in the talk, dividing them into disasters and mishaps.
The first disaster under discussion was the Dee Bridge Collapse of 24 May 1847 which occurred at the peak of railway mania. The Dee Bridge was built with three spans, masonry piers and abutments. Right from the start, Stephenson was worried about ground conditions so decided to use lighter materials. What went wrong? The 6.15pm train from Chester to Ruabon was running 5 minutes late and already doing 30mph when it crossed the first two spans, then there was a ‘crunch’. There are no photographs but Alan explained what had happened using diagrams and the very good description given by the locomotive driver. He managed to get the locomotive over and pull the tender up but 5 carriages went into the River Dee with the loss of 5 lives. Thanks to the quick thinking of the driver, warnings were given to prevent any further traffic from going over what was left of the bridge.
There were two tracks each carried by iron girders placed on oak beams over the three section 98 foot span, with reinforced joints, wrought iron supports and compound truss girders. However, there was a misconception in the design illustrated with the help of Alan’s own clear diagrams. Unfortunately, the design technique used provided insufficient strength to the overall construction. To add to the problem, additional ballast had been placed on the bridge on the day of collapse to reduce the fire hazard to the timber beams below the rails, adding extra weight which further reduced the strength of the bridge. The third factor was dynamic oscillation caused by the locomotive which was designed with a long boiler on a short wheelbase with outside cylinders approaching the bridge on a curved track; Alan’s diagrams neatly illustrated the oscillation and frequency of the bridge to show how effectively ‘floppy’ it was under the circumstances.
There were around 60 similar bridges from other designers using the same techniques which were hastily reinforced after the disaster. Stephenson admitted it was his fault and his miscalculation. Both he and contemporary designers and engineers, learning from the experience, did not make the same mistake again.
The next disaster was the well known Tay Bridge incident of 28 December 1879 when the high girder section collapsed. This was a very long bridge, and gale force winds and darkness to contribute to the difficulties. The bracings on the pillars were poorly designed and insufficiently robust and there may have been some temporary fixings still in place. The bolts holding the piers to the base were also inadequate. Tragically, the design had not allowed for the really bad weather conditions; for example, the Forth Rail Bridge was designed to cope with forces of 56lb per square inch whereas the Tay Bridge was only designed to cope with 10lb per square inch. With diagrams showing the construction and natural forces, it was clear to see how the collapse had happened. The locomotive was eventually rescued and some of the materials were later reused confirming that it was the design and construction rather than the materials that were the problem.
The third disaster occurred on 4 December 1957 at Lewisham with the loss of 90 lives. The scene was badly affected by darkness and fog when a steam train missed a red signal and collided with the rear of an electric train, made worse by curved track on the approach, and heavy traffic. A major problem was poor signal sighting which meant that the driver, with limited visibility from the cab, could not see the red signal. Photographs show how the tender was pushed sideways into the column of a bridge crossing over the track at this point. A number of issues raised by the disaster led to improvements in cab design; ensuring a safer distance between track and bridge columns; better and stronger bridge construction to withstand accidents. Alan explained present day engineering standards where there must be at least 4.5 metres distance between track and columns and any column must be able to withstand 200tons sideways force. A photograph of the bridge today shows the ‘temporary’ repair still in place using military trestling as support, a superb system that works well.
Disaster number four was the Severn Rail Bridge in October 1960 by which time the bridge was not much used. It was originally built in 1879 to get coal out of the Forest of Dean with the line funded jointly by the colliery owners and the Midland Railway. A long structure with two big spans to allow shipping through, shipping was protected by a timber structure at the base of the piers. A ship had collided with pier 17 in 1943 with subsequent repairs to make good the cast iron bracing with steel, but it appears that the fixing bolts at the top of the columns were neither properly checked nor replaced. At the time of the disaster, strengthening works were already in hand and there were photographs of the two petrol barges that collided, locked together and drifted into Pier 17. Again this happened at night in thick fog reducing visibility. Alan found an old book of very interesting reminiscences from the fireman of the last train to go over the bridge approximately 3 minutes prior to the accident. Photographs of the scene on the following morning illustrated the aftermath. Diagrams and calculations showed that there was an estimated impact of 170 tons where there was an impact limit of only 50tons. Due to the high cost of repair, the bridge was eventually taken down although demolition was not completed until May 1970. There are a few remains visible at very low tide.
After the break, Alan detailed four more ‘mishaps’ including Bexley in February 1997 where a train derailed on the bridge resulting in 4 serious injuries. Two Class 37s were hauling spent ballast wagons and at least one wagon was overloaded. The train was going at 60mph instead of the maximum permitted 40mph. The nature of the bridge construction had wood packing under the track requiring periodic replacement. Urgent repairs had been requested by the permanent way staff but had not been authorised, another contributing factor to the mishap. But the primary cause is likely to have been gauge spread of the tracks on a failing track bed, aggravated by overloading and speeding. The RAIB have issued safety advice after an incident with a similarly constructed bridge in September 2024, with the full report still to come at the time of the presentation. The sooner this type of construction is phased out the better!
Incident six was the Docklands bomb in February 1996 where 2 people died and 100 were injured with damage to the viaduct and much damage to the surrounding buildings from the blast. This was a bridge designed by Alan himself. It appears that the bridge deck lifted and went back down again relatively undamaged. Photographs showed some damage to the bridge girders which were quickly repaired.
Mishap seven covered the Stewarton Bridge collapse in January 2009, the bridge was in poor condition awaiting replacement. There was a build up of ballasting over time hiding corroding girders which were impossible to inspect properly. The final straw was a Class 66 hauling 100 ton bogie wagons. The locomotive got across but the wagons proved too much, some derailed, fire broke out and there was substantial damage although luckily no loss of life. There have been similar incidents (eg Clapham Junction signal box in 1965) showing the importance of proper inspection.
The final disaster was the Kerch Strait Bridge in Ukraine connecting Crimea to Russia. Little information as to exactly what happened has been made available but Alan provided both photographs and his own diagrams of the train of events illustrating the likely way that the spans were sucked in and came off their bearings. The railway remained in use albeit at slow speeds, but one span was very quietly replaced in May 2023 without any fanfare.
Alan then spoke generally about the causes of bridge collapse such as scouring at the base of piers and abutments of river bridges, with examples to illustrate. The good news is that most bridges do NOT collapse.
Questions and answers followed including a local incident at Feltham where the railway goes over the River Crane (scouring); what happened to the driver in the Stewarton Bridge collapse; future developments; new construction methods and materials; effective life span of concrete bridges amongst other things.
The vote of thanks highlighted just what had been learned during the evening. A brilliant and enlightening evening of civil engineering.