Blog 2
The Albert Bridge

The Albert Bridge

Structure Information

The Albert Bridge is a road bridge over the River Thames, connecting the Chelsea part of Central London to the Battersea district. The Chelsea Bridge and the Battersea Bridge were opened previously, but the link between the two neighborhoods was not adequate for the growing area so the Albert Bridge was built. The neighborhood of Chelsea expanded in the 1800’s, and Prince Albert proposed the idea of a new and improved bridge to replace the existing ones. The Albert Bridge Company was established in 1863 to build a better bridge, and an 1864 Act of Parliament authorized the construction of the bridge. [1] They were tasked with the operation of the bridge, and toll booths were implemented to generate revenue and cover the cost. [4] The engineer for the Albert Bridge was Rowland Mason Ordish of Messrs Ordish and Le Feuvre, and the construction of the Albert Bridge began in 1871 after initial delays. Ordish was supervised on the project by engineer F.W. Bryant, and the iron and steel work for the project was provided by Britannia Ironworks of Derby. The Albert Bridge was opened to the public in 1873 and given the name in honor of Prince Albert, the husband of Queen Victoria. [1] It was later modified and strengthened by Sir Joseph Bazalgette between 1884—87. The Albert Bridge was once again restored between 1972-1973 and a central pier was added during this time. Last but not least, the Albert Bridge was refurbished in 2010-2011. [1] This is hopefully the last time it will need maintenance, but better safe than sorry!

Figure 1: http://janbutcher.co.uk/?attachment_id=1525

Historical Significance

The historical significance of the Albert Bridge is that it is one of the two central London road bridges to have never been replaced (the other being Tower Bridge). The original design was a suspension bridge but the addition of cable-stays make this a hybrid type of bridge. [1] The six year delay on the start of construction for the Albert Bridge allowed Ordish to design and build the Franz Joseph Bridge in Prague. He used the same principles on the Albert Bridge as the Prague Bridge so the design was not innovative on the Albert Bridge, but he was able to patent this new design after it was utilized on both bridges. [4] In 1857 Ordish patented his system to combat dynamic movements with the catenary cables and the stays each taking a proportion of the loads. [2] The Ordish-Lefeuvre principle, as it was known, was only utilized on those two bridges. When I saw the Albert Bridge, it reminded me of the Brooklyn Bridge with the combination of cable-stayed/suspension bridge design. However, I was not able to find a direct link between the principle patented by Ordish and the Brooklyn Bridge design, which came after. The addition of a central pier in 1973 to strengthen it led to the more traditional beam bridge which still stands today. [4] The weight limit of two tonnes is present, as well as a traffic island at the southern end of the bridge to decrease the size of the vehicles which cross it. [4]

Cultural Significance

The Albert Bridge is an important part of the Chelsea Embankment and the surrounding Battersea Park area around the Thames River. [1] The toll booths were in operation for six years before the structure was bought by the Metropolitan Board of Works, who then made it free to cross the bridge. [3] Proposals to demolish the bridge began in 1926. Both before and after World War II, the Albert Bridge faced the threat of demolition; a 1957 public campaign against demolition saved the bridge. The public campaign was headed by Sir John Betjeman, who described the Albert Bridge as “shining with electric lights, grey and airy against the London sky, it is one of the beauties of the London River.” [1] After the campaign, a weight limit of 2 tonnes was imposed on vehicular traffic on the bridge to combat the fear of bridge failure, and it was almost made an entirely pedestrian bridge. [3] The Albert Bridge was therefore nicknamed “The Trembling Lady” because there was concern that the vibrations from the Chelsea Barracks would cause damage to the bridge. Soldiers from the barracks were advised to break step when marching over the bridge, but those fears and cautions are not present today on the Albert Bridge. [3] When soldiers would march in step, it would cause vibrations of the bridge. This would also occur when large numbers of people cross the bridge simultaneously, with their steps accidentally synchronizing. It’s interesting that this phenomenon happened with the opening of the Millennium Bridge in 2000, with the same problems leading to the vibration and movement of the bridge. [4] I guess we didn’t learn from the mistakes of the past!

Today, the lack of parks or open green spaces on the north side of the Thames River leads to a lot of people walking their dogs across the Albert Bridge to the Battersea Park on the others side. This would not appear to be a huge problem, except that the frequent dog urination on the timber deck causes the deck to rot. [3] However, when I walked across the bridge I did not see (or smell) that this was a problem! The bridge has been used in the background of several movies: Absolute Beginners, Maybe Baby, A Clockwork Orange, Sliding Doors, among others. [3]

Structural Art

Today the Albert Bridge is painted pink, blue and green, a color scheme that is supposed to last around 25 years. There have been numerous color schemes throughout the history of the bridge, but the reason for the most recent one is to increase visibility during fog and dim light. The bridge is supposed to be one of the prettiest bridges in London, so it has the elegance and maximum aesthetic expression part of structural art. However, the bridge started out as a cable stayed bridge but extra supports were necessary to carry the load and suspenders were added. This means the bridge did not use minimum materials so it does not satisfy the efficiency aspect of structural art. By David Billington’s definition of structural art, the Albert Bridge is not structural art.

Structural Analysis

The Albert Bridge was originally intended to be a cable stayed bridge which utilized the Ordish-Lefeuvre principle. The design for the original bridge was a suspension bridge with a “parabolic cable to help take the weight of the central span, aided by 32 inclined stays of wrought iron, inked to one of four octagonal cast iron towers.” [6] The suspension cables were made out of wire steel rope, and they took the weigh of the flat wrought-iron diagonal stays. The diagonal stays provided support for the deck of the bridge. The four towers are made out of cast-iron and stand on the four tapering piers, which are cast-iron cylinders filled with masonry and concrete. The cylindrical iron casting weight 10 tons and had to be transported down the Thames River from the Battersea foundry to the location of the Albert Bridge. The tower pairs on each side of the span are connected by a girder and arch. [6] Sir Joseph Bazalgette, the Chief Engineer of the Board of Works, made modifications on the bridge after seeing that corrosion of iron was already present in 1884. He replaces the steel cables with steel link chains and added a new timber deck. This gave the Albert Bridge more of the traditional suspension bridge appearance, and started the hybrid combination of bridge types. [1] The part which makes the Albert Bridge a suspension bridge is the “deck supported by vertical hangers suspended from catenary chains hung between pairs of towers.” The part which makes it cable-stayed is the “support of the deck from the inclined stays fanning out from the top of the tower, providing greater rigidity.” [1] Strengthening work during 1972-1973 include the addition of “two circular piers connected by a transverse steel beam beneath the middle of the bridge.” In the 2010-2011 modifications, the bridge was refurbished and repainted, and the decking was replaced once again.

Because the aspects of the bridge which make it more of a suspension bridge were added later 10 years after the original bridge opened, it can be assumed that the cable-stayed bridge was sufficient in carrying the load. For the purpose of this analysis, the Albert Bridge will be treated as a purely cable-stayed bridge because the Ordish-Lefeuvre principle is a patented early form of cable-bridge design in a modified form.

The Albert Bridge has a fan design since the cable stays fan out from one point on each of the towers. It a multiple span bridge: it originally had 3 spans before 1973, the addition of a pier in the middle of the main span made the bridge have 4 spans. The 3-span aspect of the bridge means the loads from the main spans are anchored towards the end of the abutments. In a cable-stayed bridge, the cables are in tension while the mast and deck are in compression.

The following are the current dimensions of the Albert Bridge: width of 12.5 meters, total length of 216.7 meters, main span length of 137.2 m, and a tower height of 21 m. To analyze this bridge, the first approximation is to ignore the stiffness of the deck and assume that the cable carries all the load. To simplify the analysis, assume that the cables on each side are lumped into a middle cable. The bridge has a weight limit of 2 tons, so it is assumed that the trucks which cross the bridge will have a max mass of 2 tons. The average length of a truck is 8 meters so approximately 27 trucks can simultaneously fit on one road lane on the bridge. If each truck is exactly 2 tons, then the max live load on the bridge would be 54 tons, or 17, 792 N. The live load along the whole length of the bridge is: (17,792 N)/(216.7 m)= 82.1 N/m. The tributary area for the truck will be half the width of the bridge. The live load on the bridge is calculated to be (82.1 N/m)*(6.25m)= 513.2 N

                                        Figure 2: Simplified live load on bridge

The timber deck is assumed to be English Elm, which has a density of 565 kg/m^3. To simplify the analysis, the deck will be (incorrectly) assumed to be a solid wood beam. With the assumption that the deck is solid wood which has a thickness of 0.5 meter, the dead load on the deck will be:

w = (565 kg/m^3)*(0.5 m) = 282. kg/m^2

The tributary area of the lumped cable is calculated to be:

Figure 3: Calculating tributary area of deck

The tributary area of the deck is calculated to be A=(68.6 m)*(12m)= 823. 2 m^2. Since the tributary area is 823.2 m^2, the load on the lumped cable is calculated:

W = w*A = (282.5 kg/m^2)(823.2 m^2) = (232 kg)

W= (232 kg)*(32.2 m/s^2)= 7470.4 N = 7.47 kN

The total load will then be the live load plus the dead load: 7470.4 N + 513.2 N= 7983.6 N. Since it is assumed that the lumped cable takes the weight of the deck and the live load, the following free-body diagram illustrates the forces acting on the cables:

                   Figure 4: Forces in cable

The angle in the figure above is calculated using the length of ¼ of the main span and the height of the tower. It is assumed that the height of the tower extends from the deck to the fan of the cable-stays.

Considering one cable in equilibrium the following forces are present:

The tension force in the cable is calculated to be 14, 167 N, and the compression force in the deck is calculated to be 11,704 N. A typical cable-stay diameter is 90 mm, so the area is 0.636 m^2. The stress on the cable-stay will be the force divided by the area, or 11,167 N/0.636 m^2= 17,553 Pa.

Personal Response

Going to see the Albert Bridge in person, I had high expectations due to the many praises it has received as the prettiest bridge in London. I thought it was a pretty bridge, but it did not seem like anything amazing. I think this is because the span and height of it seems small in comparison to some other bridges, where the sheer size of the bridge is what makes it so impressive. I think the colors are definitely a nice touch in comparison to other bridges, especially during the time of the day that I visited the bridge and snapped a picture in good light. I think seeing the bridge at night with the lights on would have made it seem even more appealing.

References

  1. https://historicengland.org.uk/listing/the-list/list-entry/1358138
  2. https://www.bristol.ac.uk/civilengineering/bridges/Pages/NotableBridges/Albert.html
  3. https://londonist.com/2016/10/secrets-of-albert-bridge
  4. https://alondoninheritance.com/tag/albert-bridge/
  5. http://www.interserve.com/latest-insight/2010/refurbishment-of-albert-bridge
  6. https://www.britainexpress.com/London/albert-bridge.htm

 

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