William Fairbairn And The Box Girder
During the 1800s, the industrial revolution increased the demand for raw materials, as the rate of manufacture in towns across the country increased exponentially. These materials had to be transported over large obstacles in order to reach the factories, this prompted an unprecedented need for better, more stable infrastructure which, in turn, increased the demand for new engineers to contribute in the push for innovations.
Sir William Fairbairn, born on February 19th, 1789 was a Scottish civil engineer and inventor who did revolutionary work on the design of bridges. Through his testing procedures, William was able to find new applications for iron. This allowed him to contribute to the invention of the box girder which enabled the construction of new, longer span bridges which could carry loads previously too heavy to support. Although widely known for his contribution to the box girder and the bridge developments associated with the design, William’s other contributions to society must be noted and credited. These acknowledgements will give an idea about how William Fairbairn came to acquire the knowledge to help in the box girder design and whether this was even his most significant invention.
The Career and life of William Fairbairn
Fairbairn experimented with the strength of iron through the testing of new design shapes as well as using hot and cold blast during the iron manufacturing process. He was also known to conduct investigations on the failure of structures. This, combined with design experience enabled Fairbairn to avoid design mistakes and to spot fatal design errors by others, this was evident during William’s career.
Between 1817 and 1832 William began his career with a partnership with James Lillie where they worked as Manchester Millwrights, together they set up the Fairbairn and Lillie business. William made improvements to water wheels and mill wheels and the company established a good reputation. The business went on to expand into Europe.
In 1835 William visited Millwall, London. Here he established a shipbuilding yard where he continued to build hundreds of boats. In 1839 Fairbairn began building 0-4-0 design steam locomotives which would then be transported to the Manchester and Bolton railway. This design was simple and by 1962 William’s company had successfully built around 400 of these locomotives which were then transported by road to the tracks to be used. Throughout this time Fairbairn produced the locomotives for the London and North Western Railway and the Great Western Railway.
During 1844 William, alongside John Hetherington introduced the Lancashire boiler. During the development of this, William conducted tests on pressurized glass tubes, these tests showed that the diameter of the tube experienced the most stress. This stress was known as hoop stress, upon discovering that as the diameter increased, the hoop stress also increased, Fairbairn realised that reducing the diameter of a tube would reduce the amount of hoop stress acting on the tube wall. William applied this principle to development of the Lancashire boiler which contained two smaller flues containing fires rather than only the one larger flue that the conventional boilers had. This change allowed for a cheaper boiler shell, it was now also easier to maintain a fire inside the boiler. The change also allowed the boiler to become more durable and withstand greater internal pressure.
In 1846 William advised Robert Stevenson against a choice of girder design on a bridge spanning over the River Dee in Chester. Robert ignored William’s advice, choosing instead to go ahead with the project. In May 1847 the bridge collapsed resulting in the death of 5 of the train passengers.
In 1853 William founded the Manchester boiler association. This later became known as the Manchester steam user’s organisation and became responsible for setting the standards for high pressure steam boilers.
In 1961, upon being commissioned by the UK parliament, William conducted research into Metal fatigue due to applied loading. To investigate this subject, William applied three tonnes of weight onto a wrought iron test cylinder before removing it, this procedure was then repeated three million times until the iron failed. From this test, it was concluded that a static weight of twelve tonnes could be supported by the test cylinder before failure occurred. This allowed the government to increase their understanding of the behaviour of iron used in manufacture. In 1865 Fairbairn purchased the Redhill street mill in Manchester. Here he installed new spinning mules that were larger and fully automated, this enabled the rate of cotton spinning to be increased. This mill was incredibly successful and became the largest mill in Manchester. On August 18th, 1874, William died because of a bronchial cold.
The box girder and its construction methods
A box girder is usually built from structural steel or prestressed concrete. Concrete use is generally more popular partly due to the lower maintenance required in comparison to steel. This is because concrete box girders do not require any protective paint coatings. Structural steel is generally used for box girders making up bridge spans greater than approximately 200 metres. The cross-sectional shape of the box girder is that of a rectangular or trapezoidal hollow box consisting of two webs and two flanges, although having two webs is more expensive than a single web girder design, the box girder can hold a greater amount of weight than an I beam that uses the same amount of material. This enables the box design to usually be more cost effective for longer spans that experience heavier loads. The box girder bridge also requires a lesser number of support columns than a bridge using an I beam.
The box design allows for a greater strength per unit area to be achieved with the same concrete used, this increases the design efficiency. The box shaped profile of the girder also allows for a greater torsional stiffness and strength as well as an increased aerodynamic efficiency in comparison to a standard I beam. By having a hollow middle, the slab thickness can be decreased, and this lowers the self-weight of the bridge. Box girders can be used in the construction of long span cantilever designs such as the Kanawha River Bridge in West Virginia which is able to span 231 metres. The box girder would most likely be pre-fabricated and transported to the site. Although the prefabrication allows for a greater quality assurance and would be faster than making the girder on site, the transportation may be difficult especially when building in water or on a site with difficult road accessibility. Concrete box girders can be constructed using in situ concrete, if concrete is cast in situ, travelling formwork would be used allowing the previously constructed bridge deck to support the weight of the freshly poured concrete mix. The structural steel girders are usually expensive therefore would be used on larger, well-funded projects. Box girders are still used in some bridge constructions today, encouraged additionally by the lack of traps for dirt and moisture, this allows the box girder to remain durable enabling a lesser need for maintenance.
The development of the first box girder bridge
During 1845, in the design of a railway linking London to Anglesey, a major obstacle was present, the Menai Strait. This was a very strong tidal zone. With a width of approximately 350 meters, this body of water would prove a major problem when carrying a train of significant weight across. This led to the creation of the Britannia bridge. The challenge of designing a bridge strong enough to hold the weight of a train yet remain structurally sound was given to Robert Stephenson due to his recognition as one of the best civil engineers of the time. Robert then appointed William Fairbairn and Eaton Hodgkinson to work with him. To overcome the problem, William Fairbairn originally tested weights on a tubular design for 6 weeks. In this experiment, a tube was attached to two supports and a load was placed in the middle where the maximum bending moment would occur, weights were added until the tube buckled. Upon the bucking of the tube, reinforcement material would be added to the areas experiencing the most stress to allow the tube to carry more weight. The experiment concluded that a tube design was not adequate. This led to the boxed shape which was found to be effective as it was the only shape able to carry the target loads. This founded the invention of a new, box girder design. The box girders were constructed using wrought iron and were pre-fabricated, riveted by hydraulic machines also designed by William Fairbairn. To transport the box girders to be positioned, they were floated to the bridge and lifted into place. During the design of the Britannia bridge, the railway passed through the middle of the girder rather than on top of the span, because of this, the structure was known as a tubular bridge. Eventually, box girder bridges became less common having been replaced by plate girder and lattice girder bridges. However, luckily for Fairbairn, the factories he owned could produce these more popular designs allowing William to continue to make an income. There have been reports of more recent box girder bridge failures that resulted in complete collapse, this includes bridges in Wales and Australia. Because of this, a revaluation into the safety of box girder bridges was conducted, ultimately further decreasing their usage.
The future of box girders
Due to their strong design, box girders can still be used to produce bridges that are at the forefront of modern bridge building technology. An example of this could be the cable stayed box girder bridge, here the girders would be supported by cables attached at intervals. The cables, put in tension, are attached to a main pylon which is positioned at an angle. Through this design, the box girders can support spans previously unable to be reached by a pier supported box girder.
Curved box girders are now able to be produced using modern computer modelling technology. This allows for the creation of a precisely curved bridge such as the Fossdyke bridge in Lincoln. Recent research has suggested that the trapezoidal box girder is the strongest shape in comparison to the rectangular and circular box girder. Considering this, future box girder bridge designs may be able to support increased loads than previous box girder bridges could. Their aerodynamic shape also further decreases wind resistance causing a reduction in wind loading. In the experiments conducted by Karthika Santhosh and Professor P Asha Varma, it was concluded that the maximum bending moment for the dead loading was lowest in the hexagonal box girder for both curved and straight sections when compared to the bending moment experienced by the rectangular and circular sections. This hexagonal design has been used in designs such as the Alamillo bridge in Spain.
Despite his fame during the 1800s, there is very little information on the life of William Fairbairn. This is partly due to how lots of information about his companies were destroyed. Despite publishing books, William never published any letters or papers, making this project more difficult than anticipated.
Lots of the box girder research was from PhD reports and from steel construction websites, this allowed it to be trustworthy and reliable. Any information taken from less well-known sources was cross referenced to ensure legitimacy. It is important to note that, because the information recorded about William’s life was from the 1800s, we must rely on the original records being factually accurate and having been unaltered throughout the last two hundred years. Few of the sources were primary therefore exaggerations may have occurred, and details forgotten during the passing of information to the secondary sources.
From the insights obtained through the works published since his death, an understanding has been developed of the fact that Fairbairn was a vital engineer of the 1800s. Not only for his significant contribution to the invention of the box girder but also for his major influence in the running of the mills in Manchester, the production of England’s ships and boilers and his invaluable consulting expertise obtained through vigorous testing of materials. Combined, these accomplishments suggest that Fairbairn should not be remembered purely for his influence on the production of the box girder, but more for the reminder of the importance of research. The box girder design was important not only for its significant technological push on 1800s bridge building techniques, but also the impact the box design has had on the bridges around us today. The box shape has continued to evolve, allowing new contributions to improve the original design that Fairbairn and Hodgkinson proposed 173 years ago.
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