The Bridge Stress Committee was appointed in 1923 by the UK Department of Scientific and Industrial Research under Sir Alfred Ewing, to investigate stresses in railway bridges, especially as regards the effects of moving loads. Its report, published in 1928, was very influential in British locomotive design as it enabled larger multi-cylinder locomotive classes.

Background

The increased weight of express trains in the United Kingdom during the first quarter of the twentieth century required larger, six-coupled locomotives, but new designs were being limited by the weight restrictions imposed on many underline bridges. On most mainlines this was restricted to no more than on any axle. However, engineers were becoming increasingly aware of the significance of ‘

hammer blow In rail terminology, hammer blow or dynamic augment is a vertical force which alternately adds to and subtracts from the locomotive's weight on a wheel. It is transferred to the track by the driving wheels of many steam locomotives. It is an out-of ...

’ rather than ’deadweight’ in determining the safe loads for such bridges.

Committee

A committee of was established in 1923, funded jointly by the UK government and the

railway companies This is an incomplete list of the world's railway operating companies listed alphabetically by continent and country. This list includes companies operating both now and in the past. In some countries, the railway operating bodies are not compani ...

, to carry out investigations in to the effects of hammer blow on bridges. The committee under chairmanship of the physicist Sir

James Alfred Ewing Sir James Alfred Ewing MInstitCE (27 March 1855 − 7 January 1935) was a Scottish physicist and engineer, best known for his work on the magnetic properties of metals and, in particular, for his discovery of, and coinage of the word, ''hy ...

consisted primarily of railway civil engineers, but

Sir Henry Fowler Sir Henry Fowler, (29 July 1870 – 16 October 1938) was an English railway engineer, and was chief mechanical engineer of the Midland Railway and subsequently the London, Midland and Scottish Railway. Biography Fowler was born in Evesham, ...

Chief Mechanical Engineer Chief mechanical engineer and locomotive superintendent are titles applied by British, Australian, and New Zealand railway companies to the person ultimately responsible to the board of the company for the building and maintaining of the locomotiv ...

of the

London Midland and Scottish Railway The London, Midland and Scottish Railway (LMSIt has been argued that the initials LMSR should be used to be consistent with LNER, GWR and SR. The London, Midland and Scottish Railway's corporate image used LMS, and this is what is generally ...

was also later invited to join. Among the results was a better understanding of hammer blow and the effects of

oscillation Oscillation is the repetitive or Periodic function, periodic variation, typically in time, of some measure about a central value (often a point of Mechanical equilibrium, equilibrium) or between two or more different states. Familiar examples o ...

s in both locomotive springs and bridges. One immediate impact of the investigations was an easing of the axle-load limit for locomotives with both inside and outside cylinders from to . This enabled successful new designs such as the

GWR 6000 Class The Great Western Railway (GWR) 6000 Class or King Class is a class of 4-6-0 steam locomotives designed for express passenger work and introduced in 1927. They were the largest locomotives built by the GWR, apart from the unique Pacific ( ''The ...

and the fitting of larger boilers to Gresley A1 class.Nock (1983) 232.

References

* * * {{cite book , author = Department of Scientific and Industrial Research, Bridge Stress Committee , title = Report. , location =London , publisher= HMSO , date=1928 Civil engineering Railway bridges