|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Tue Oct 18, 2011 5:55 pm Post subject: Professor Sir John Fleetwood Baker (1901-1985)
|Professor Sir John Fleetwood Baker (1901-1985)
Sir John Fleetwood Baker, (19 March 1901 – 9 September 1985) was a British scientist and structural engineer.
In 1943, when John Fleetwood Baker was elected Head of Department, Cambridge University Engineering Department was staffed by 24 lecturers and there was one other chair.
By 1968 when he retired there were 111 teaching staff, and 26 members of staff had left Baker’s teams to become Professors at other universities.
John Baker Soon after he came to office, Baker put forward plans to revise the Tripos, introduce post graduate courses and develop research. Complete proposals for the development of the site were ready by 1948 and the block which is now known as the Baker Building attracted the first funding to become available for university building programmes after the war. Building was started a year later and completion with an opening by the Duke of Edinburgh, took place in 1952.
One of the graduate courses introduced by Baker on ‘Theory of Structures and Strength of Materials’ led in 1964 to the Advanced Course in Engineering Design Methods, which has now become ‘The Advanced Course in Design, Manufacture and Management’ (ACDMM).
Born on March 19, 1901, the son of Emily and J.W. Baker's young adult years matched the First World War.
Baker had read Engineering under Inglis,at Rossall and Clare College, in Cambridge, England and obtained a first class honours degree in 1923. After graduating he worked for the Air Ministry on the structural problems of airships. In 1928, he married Fiona Mark MacAlister Walker. In 1929, at the age of 28, Baker contracted tuberculosis and was told he would never be able to work again. However, economic necessity drove him back to work as a Technical Officer with the Structural Steel Research Committee.
A 1920's airship
This committee aimed to produce a code of practice for the design of steel framed structures. Tests carried out on real buildings in the 1930s showed that stresses measured on site bore little relation to those calculated using the code of practice. It was this revelation that led to Baker’s life work in the development of a plastic theory of design. This led to a revolutionary method of steel design, which was of immense value during the second world war, and was continued afterwards by his team at Cambridge.
In 1933, Baker became professor of engineering at Bristol University, in Bristol, England. With the outbreak of the Second World War, he was a scientific advisor to the Design and Development section of the Ministry of Home Security from 1939 to 1943.
The War Years
Baker’s first concern was to reduce the vulnerability of buildings to bomb attacks, in particular some of the large factories. He also set up a nation-wide network of engineers to make technical reports on bomb damage, the first application of what became known as Operational Research.
In particular, the air-raid shelters then in existence were found to be inadequate, and at the request of Herbert Morrison, the Minister for Home Security, Baker was asked to deal with this problem. It had been estimated that once air raids began the casualty rate would be of the order of 35,000 people a day. Not only did Baker come up with a way of improving existing shelters, but he also designed a new type of indoor table shelter, known as the Morrison shelter, of which over 1.25 million were distributed to householders, saving countless lives.
This intense period of high pressure work during the war years not only added greatly to Baker’s research experience, but also showed him the importance of addressing problems in production engineering using scientific methods and the value that social scientists could have on management issues. He came back to Cambridge in 1943, and believing that the war was coming to a victorious end, spent considerable time on planning the future of the Department.
The Baker Years
Many look on the ‘Baker years’ as the transformation of the Department in terms of research. A Structures Research Laboratory was set up in 1944, where work on the plastic theory of structures continued, together with research into residual stresses in welded joints, brittle fracture and fatigue.
Baker Building South Wing, CUED
The site of the Welding Institute at Abington (now TWI), about 7 miles south of Cambridge was bought in 1946 to accommodate this research into welded structures, and Dr Richard Weck left the Department to become its Director.
This can be considered the first ‘spin-off’ from the University, and the start of what is now referred to as the Cambridge phenomenon.
Baker was made a fellow of the Royal Society in 1956, knighted in 1961 and made a life peer in 1977. He accumulated numerous academic honours during his lifetime and joked in later years about whether he could acquire gold medals faster than grandchildren.
John Baker demonstrated the difference between elastic and plastic behaviour of steel beams by simple experiments.
By working to the point of plastic collapse, designers were asked to think differently about structures.
See Videos: http://www-g.eng.cam.ac.uk/125/media/video/baker_elastic.mpg
Prof. Baker demonstrating the difference between elastic and plastic behaviour
Very simplistically, instead of working out what the loads on a structure are likely to be and then making that structure twice as strong (elastic design) designers worked out what load would make them collapse, and then make them able to withstand twice that load.
Elastic theory does not accurately model the stresses in real buildings because the equations are very sensitive to small anomalies in a real structure. Thus a small settling of the foundations or a slight error in the manufacture of the length of a steel girder can give very different stresses to those calculated. That is why Baker considered elastic solutions not to be a proper design tool for structural frames.
Plastic Theory - Morrison Shelter
The most spectacular application of Baker’s plastic theory was to the ‘Morrison Shelter’. At the start of the Second World War almost all the standard forms of air raid shelter were unsatisfactory.
These shelters were designed to squash down plastically by no more than 12 inches if the house collapsed as a result of a bomb.
The Morrison shelter was less than 1 meter tall, a little under 2 meters long, and a little over 1 meter wide – just large enough for a few people to fit in while lying down. Similar to the Anderson shelter, it came in a kit. The Morrison shelter was said to have over 300 separate parts and pieces, but when assembled was a simple box-like structure with a solid steel top plate, welded wire mesh sides, a metal base and mattress floor. The sides of the shelter could be taken off, so it could be covered with a cloth and used as a dining room table during the day. According to a page on the Rayleigh Primary School website, "Over six hundred thousand Morrison shelters were ordered between 1940 to 1944." The site also detailed a study of the shelter's effectiveness by the government, finding that out of 44 heavily damaged homes with Morrison Shelters, "of the 136 occupants, 3 were killed, 13 seriously injured and 16 were lightly injured. It also found that the fatalities were caused by direct hits from bombs."
This video clip shows Baker lecturing on his famous invention, which saved countless lives and for which he won £3000.
Morrison Shelter video
Fundamental theorems of Plastic Design
In the twelve years from 1936 to 48, Baker had developed his work on Plastic theory to the point where it could be used in practice. However the fundamental theorems had yet to be formulated.
In 1948, Baker set up a collaboration with W.Prager at Brown University, through which the rules for plastic design were finally arrived at. A two volume account of the history of the steel skeleton was published by Baker in the 1950s, and in the 1960s the plastic theory became central to undergraduate teaching (I have the two volumes authored by Prof. Baker).
The plastic theory of design, a revolutionary method of design of steel structures, gives a lower bound on the collapse load, and hence always safe. Until then, all design of steel structures was based on elastic theory of design, which gives an upper bound on the collapse load.
During his time at Cambridge, plasticity theory was used to design the new Baker Building of the department, making it the first building in the world designed by this method.
Lord Baker left all his papers to the Churchill Archives Collection on his death in 1985.
Despite its intellectual attraction, the practical application of plastic methods advanced only slowly. With the advent of computers, the present day practical designers have discarded rational plastic methods for the design of straightforward structures, as the elastic calculations have been computerised and are easier to use. However, there are critical applications where the use of plastic theory is coming to the fore, such as the recent work on bridge evaluation carried out by Dr. Cam Middleton and his team from this Department.
Code changes due to Prof. Baker's work
As a result of Baker’s work, the British Standard 449 was modified by the insertion of a clause to permit plastic design in 1948. The Welding Institute at Abington became a showcase for examples in plastic design of buildings. Three separate examples also exist at the Engineering lab in Cambridge.
Picture of the Welding Institute
Plastic theory, as developed by Baker and his team became a central part of the undergraduate course at Cambridge in the late 1960s. It can be applied to any material that is used for building, from a medieval cathedral to a skyscraper. Use of this theory is now saving the taxpayer millions of pounds in its application for the evaluation of the safety of road bridges.
Baker was the recipient of numerous academic honors. Additionally, he was made a fellow of the Royal Society in 1956, knighted in 1961, and made a life peer as Baron Baker, of Windrush in the County of Gloucestershire in 1977.
2. Heyman, J., Royal Society Biographical Memoirs. John Fleetwood Baker, Baron Baker of Windrush. 1985
4. Christina, M.Zweig, John Fleetwood Baker -Wartime Innovator, Structural Engineer, Oct 2011, pp.34