The Principle of Transferring the Weight of the Bridge - Essay Example

?Introduction Several bridges have been erected in London to cross the river Thames and each and every bridge is important because of its very own uniqueness. Some bridges have a history of their and they have now become cultural landmarks, while the techniques employed for their renovation and reconstruction have made them architectural and structural landmarks. In this report 4 bridges from London have been selected and their brief details along with comments on their designs have been stated. Binary Dominance Matrices are used for two bridges to establish various salient features of the bridges. Waterloo Bridge Type of Bridge: Traffic Bridge Purpose: To facilitate road and foot traffic Age: 194 years Dimensions: The span of the bridge is 120 feet and the total length between abutments is 1240 feet. Materials: The original bridge was constructed from granite stones but the in the second bridge latest technology at that time was used and concrete beams and slabs were used along with concrete piers for the construction. Along with the reinforced concrete the architectural work is done by grey Cornish granite and Portland Stone. Opinion about the design The use of reinforced concrete beams under the footways and the road supported by slabs is a very good design by strength point of view but if we consider the aesthetics and the building heritage of London the original design of the bridge should have been preserved by using arches. This would also have eliminated the need of the cantilevers which are present now. The design calls for supporting beams only at the outside edges, which is actually a very good feature as it lets light enter the underside of the bridge which makes it very pleasant for the river traffic. To guard against the possibility of subsidence from scour the piers are given jacks which can be used to level the structure. The architecture of the bridge is also important and in order to preserve the building architecture of London various stones, mainly the Portland stone has been used in cladding. Millennium Bridge Type of Bridge: Steel Suspension Bridge Purpose: To facilitate pedestrians crossing river Thames in London Age: 9 years Dimensions: The width of the bridge is 4 meters (13 ft) and the total length is 325 meters (1066 ft). It can support 5000 people on it at a time. Materials: The Millennium Bridge is mainly constructed of steel with steel cables and steel armatures. The transverse arms are also made of steel while the deck of the bridge is made of aluminum as it is a very light metal and the use of aluminum in the deck has reduced the load on the armatures and cables. Opinion about the design The design of the millennium bridge is basically steel suspension design which initially posed some problems and the bridge was ultimately closed just after 2 days of its 1st opening due the intense vibrations due to resonance. But the corrections were made later during a period of 2 years. The use of aluminum deck is the best feature of the design in my opinion because since it is a pedestrian bridge the strength of the deck is not an issue here so in order to make the design cost efficient and sustainable the loads on the cables and armature have been lessened by the use of aluminum in the deck which is a very light material as compared to steel or concrete. Moreover while designing a bridge entirely of metallic structure proper considerations should be given to the design as the modifications are very difficult and costly in nature as the case of the millennium bridge tells in which the bridge was closed for 2 years and an additional cost of 5 million pounds was spent on the modifications. Tower Bridge Type of Bridge: Bascule and suspension bridge Purpose: Tower Bridge is basically a road bridge for usual traffic Age: 116 years 7 months Dimensions: The total length is 286.5 meters. The two side-spans are suspension bridges, each 270 feet (82 m) long. The pedestrian walkways are 143 feet (44 m) above the river at high tide. Materials: The towers are made of steel while the deck of the main bridge is also made of steel. The veneers are made from brick masonry. Opinion about the design The London Tower Bridge design is both aesthetically pleasing and functional. The two huge towers suspend which suspend an upper walkway for pedestrians and also suspend a lower road for vehicles are the key features of the bridge aesthetics and as well as the bridge design. Alongside the roadways there are side walkways for the pedestrians as well. The tower bridge design is very comprehensive and has accommodated in it perfectly, all the requirements for which it has been constructed. The lower road is comprised of two halves, which can be raised up to allow ships to pass. This allows the river traffic to move very smoothly as well. Initially the bridge was powered by steam and later the steam pumps were replaced by electric pumps. Now the bridge is powered by hydraulic press which is the best design possible as it requires the least energy and is also very safe for the materials which are present in the structure of the bridge. The most salient feature of the design are the two massive piers which contain over 70000 tons of concrete and are sunk deep in to the riverbed to support the bridge. Over 11000 tons of steel is used in the framework for the towers and the walkways. The architectural work is done in the form of stone cladding by Cornish granite and Portland stone. This stone cladding is dual purpose as it is aesthetically good for the bridge and it also provides cover to the steel and protects against rusting and corrosion thus enhancing the life of the structure. London Bridge Type of Bridge: Arch Bridge Purpose: Tower Bridge is basically a road bridge for usual traffic Age: The place where the London Bridge is present today has been occupied bridges over the last 2000 years and the first bridge on this location dates back to as early as 50 AD. The present bridge was opened in 1973 so the age of the present bridge is more than 37 years. Dimensions: The total length is 262 meters. The span of the bridge is 32 meters while the largest span of the bridge is 45.6 meters. Materials: In past London Bridge was constructed from stone arches as well as iron and steel arches. Haytor granite was also used in the 19th century London Bridge. The materials used in the modern London Bridge are pre-stressed concrete and box girders. The architectural work is done by stone cladding. Opinion about the design The present London Bridge comprises of three spans of prestressed-concrete box girders. Like a simple arch bridge, London bridge design works on the principle of transferring the weight of the bridge and its loads partially into the form of horizontal thrust restrained by the abutments on the sides. London Bridge is a viaduct which has been made form a series of arches. Each arch is constructed as a compression arch bridge and thus it requires the bridge to be heavy so that the more the weight is put on the bridge the higher is the strength. The reason behind making London Bridge an arch bridge is to conserve the city building heritage of London. As compared to traditional arch bridges, London Bridge is not very heavy because of the modern materials used in it which includes the concrete additives to make it a bit lighter. Moreover the mechanism in which the weight is shifted to the ground is also different from the traditional arch bridges and is somewhat similar to the cable suspended bridges in which the cables are anchored in the ground at the banks of the river. In the modern London Bridge the reinforcement of the concrete of the extreme arches is shifting the load to the ground. Moreover since London bridge is made up of a series of arches, piers have also been used to transfer the load to the river bed. The use of reinforced concrete is useful and suitable as temporary centering technique is now available for constructing the arches from concrete. In this technique the arches are built in two halves and this is the case with the design of the London Bridge. The load transferred to the abutments is less in case of London Bridge as some of the load is bore by the tension within the bridge structure and this has actually increased prospects of this London bridge to stand more than the previous ones as it solves the issue of load transfer to the soft Lambeth clay at the banks of Thames. Binary Dominance Matrix for London Bridge Criteria A B C D E F G H I J Total A Legislation - 1 0 1 1 1 1 1 0 1 7 B Capacity 0 - 0 1 1 1 1 0 0 1 5 C Strength 1 1 - 1 1 1 1 1 1 1 9 D Aesthetics 0 0 0 - 0 1 1 0 0 1 3 E Sustainability 0 0 0 1 - 0 0 0 0 0 1 F Energy Conservation 0 0 0 0 1 - 1 1 0 0 3 G Quality 0 0 0 0 1 0 - 0 0 1 2 H Comfort 0 1 0 1 1 0 1 - 0 1 5 I Health & Safety 1 1 0 1 1 1 1 1 - 1 8 J Cost 0 0 0 0 1 1 0 0 0 - 2 Relative Weightage of Different Criteria Binary Dominance Matrix for Millennium Bridge Criteria A B C D E F G H I J Total A Legislation - 1 0 1 0 1 1 1 0 1 6 B Capacity 0 - 0 1 1 1 1 0 0 1 5 C Strength 1 1 - 1 1 1 0 1 1 1 8 D Aesthetics 0 0 0 - 0 1 1 0 0 1 3 E Sustainability 1 0 0 1 - 0 0 0 0 1 3 F Energy Conservation 0 0 0 0 1 - 1 1 0 0 3 G Quality 0 0 1 0 1 0 - 0 0 1 3 H Comfort 0 1 0 1 1 0 1 - 0 1 5 I Health & Safety 1 1 0 1 1 1 1 1 - 1 8 J Cost 0 0 0 0 0 1 0 0 0 - 1 Relative Weightage of Different Criteria The two binary matrices of the millennium bridge and the London Bridge shows that strength and health and safety are the two criterion which cannot be compromised in any design. While the value and weightage of aesthetics and cost is different in both the designs, this is because of the fact that the two bridges are in different era of construction and the practices followed in the different eras are different. Binary Dominance Matrix should be given consideration while designing bridges as it is a very useful tool to find out the criteria which is most important among the others. Reference List Speaker M. (2004), The London Tower Bridge, Blackbirch Press. Koebrugge B. (1988), Tower Bridge, London, Stitching Prometheus. Bennett D. (1997), The Architecture of Bridge Design, Thomas Telford. Jackson P. (2002), London Bridge: a visual history, Historical Publications. Miller F. P., Vandome A. F., McBrewster J. (2009), Millennium Bridge (London), VDM Publishing House Ltd. Tonias D. E., Zhao J. J. (2007), Bridge Engineering, McGraw Hill Professional. Read More