Tower Bridge: Suspension And Bascule Bridge In London

History of Tower Bridge

Tower Bridge is a combined suspension and Bascule Bridge in London constructed from 1886 to 1894. The bridge has the become the iconic symbol of the London and it crosses the Thames river close to the London tower. The bridge comprises of two bridge towers tied together by two horizontal walkways tied together at the upper level constructed to withstand the horizontal forces caused by the suspended section of the bridge on the tower’s landward side. The vertical components of the forces in the section suspended and the vertical reaction in a two walkway are carried by two towers. The bascule pivots and operating machines are housed in the base of every tower. The deck of the bridge is accessible to both vehicles and pedestrians. This research paper was about the hydraulic bridge and the selected named one is the tower bridge which falls under suspension and Bascule Bridge. It is based on the machines that lift the part of the bridge so that it can allow the river traffic under it to pass. The bridge is near the harbor so it was important for it to be designed in the type that can enable the ships to pass. The machines that were replaced by the electro hydraulic drive were left in the museum of the tower bridge to attract the tourists.

System and functional analyses

A great problem faced the London city which was how to construct a bridge downstream from the London Bridge without affecting the activities of the river traffic. The produce the ideas, the subway committee was organized and opened the designs for the new crossing to the competition publicly. More design were forwarded fir the consideration and then the contractors chose design for the tower bridge as the solution (Billington, 2015).

It is open to the public and forms the basis for the museum of the bridge, which resides in old rooms of the engine on the bridge’s south side. The museums comprises the steam engines, 2 accumulators, and one of the engines of hydraulic that moved to the bascules along the related artefacts. The exhibitions are normally carried out on the bridge walkways, it uses the photos, films, and the interactive displays to explain how the tower bridge was constructed, the bridge was also used for the recreation and also it helped  the people to pass form one side to another (Blockley, 2012).

The construction of the tower bridge started in 1886 and took around 8 years with the five main contractors. Two massive piers with more than seventy thousand tons of the concrete were sunk into the riverbed to support the building. More than eleven thousand tons of steel gave the framework for the walkways and the towers. This was later clad in the granite and stones of Portland to protect the fundamental steel work and provide the bridge with an attractive look. In 1974, the operating mechanism was replaced by the hydraulic system, designed with original pinions driven by the modern hydraulic gearings and motors. A computer system was installed to control the lowering and raising if the bascules slightly. It proved unreliable, causing the bridge to be stuck in closed or open positions on many events until the sensors were replaced. Facelift o the bridge occurred in 2008 where the work comprise the stripping off the available paints and repaint in white and blue. Every section was covered in scaffold and sheets of plastics to ensure that the old paints don’t fall in the Thames River to cause pollution (Brangwyn, 2014). The walkways were constructed and renovated and within the walkways, a lighting system was installed to help when the walkways are used for the exhibitions and functions. The system helped in providing the atmospheric lighting, and was designed to be hidden within the superstructure of the bridge and fixed without the drilling (Council, 2016).

Construction of Tower Bridge

 The tower bridge was closed to all the roads for about 3 months, to allow the structural work of maintenance to occur. The work were; doing main maintenance to the systems that lifts the bridge. Substituting the decking and rematerializing the roads and walkway, substituting the joints for expansion along the bridge to give a smooth surface and structure, waterproofing the arches designed from the bricks on the slants to the bridge (Duan, 2017).

The tower bridge is eight hundred feet long with the two towers every two hundred and thirteen height, designed on the piers. The span at the center of two hundred feet between the towers is divided into two similar leaves or bascules which can be raised to 87 degrees to allow the traffic in river to pass. The bascules with the mass of more than one thousand tones are counterbalanced to reduce the force needed and enable the raising within five minutes. The two side spans are the suspension bridges every two hundred and fifty length with the suspension rods anchored at the abutments and through the rods confined within the upper walkway of the bridge. The pedestrian walkway are the one hundred and forty three feet above the river at the high tides (Edward, 2013).

The major deck of the bridge carries two lanes of the traffic roads between low level walkway of the pedestrian across the spans of suspension and the opening the section of bascule of the bridge, with the walkway divided from the roads by the fences. The roads passes through the two towers whereas the walkway of low level passes around the outside the towers. One of the bridge’s chimneys normally thought to be the posts lamps connects to the old place of fire in the guardroom of the tower (Frangopol, 2016).

The raising mechanism was given the power by the stored water in numerous accumulators of hydraulics. The system was constructed and fitted then water at a high pressure was pumped into the accumulators by the stationary engines of steams installed with the Mayer slide expansion valves. Every engine made a force pump from its tail piston rod.  Every accumulators consists of 20 inch where sits a heavy, as to maintain the pressure desired. The whole hydraulic mechanisms and the gas systems for lighting was fitted. Initially the gas lighting was by the open burners of the flames within the lantern but were improved to the incandescent system. The original machines for operation were replaced by the electro hydraulic drive system. The constituents of the original system still applied are the final pinions that engage to the racks installed to the bascules. They are controlled by the hydraulic gearings and motors using the as the hydraulic fluid instead of water. Some of the hydraulic machinery has been retained, even though it is not used nowadays (Frangopol, 2016).

Operation and Maintenance of Tower Bridge

To control the passage of the traffic river through the bridge, many dissimilar rules and the signals were used. The control at daytime was given by the signals of the red semaphore, placed on the small control cabins on end of the piers of the bridge. At night hours, the lights that are colored were used in both directions and on every piers, 2 red lights to display that the bridge was closed and 2 green to show that the bridge was open and a gong was sounded in the foggy weather (Langmead, 2014).

The vessels that passes through the bridge had to show the signals:  at daytime, the black ball which is two feet in diameter was placed high up when it could be seen by everuyone.at night, 2 red lights were mounted in the same position. The foggy weather require the repetitive blasts from the whistle steam of the ship. If the black ball is suspended from the center of every walkway this show that the bridge count not be opened (MacDonald, 2014).

Traffics

The tower bridge is very busy crossed by more than forty thousand people daily. To maintain the structure’s integrity, the corporation of the London city has imposed 32km/pour restriction of the speed, and a limit of eighteen tons mass on the vehicles that use the bridge. The system of camera is used to measure the traffic speed crossing the bridge using the recognition system of the number plate to send the penalty that is fixed to the speeding drivers. Another system monitors the parameter of the vehicles, the piezoelectric sensors and the induction loops are used to measure the mass and the axle’s number in every car (MacDonald, 2013).

River; the bascules are raised around one thousand times yearly. The traffic in the river is decreased but still takes the priority over the traffic of the road. The notices are needed before the bridge is opened and the times for opening are published in the website of the bridge in advance. When requiring to be raised for the vessel passage, the bascules are raised to the sufficient angle for the vessel to pass under the bridge safely (Macaula, 2015).

When it was built the tower bridge was the longest and largest and most sophisticates’ type of the bascule bridge ever completed. These bascules were controlled by the hydraulic machines that uses the steam to produce the power for pumping the engine. The energy generated was stored in the 6 huge accumulators, when the power was needed to lift the bridge it was normally available. The accumulators fed the engines for driving which control the bascules down and up. Despite the fact that the system was complex the bascules took a minute to raise to their highest angle of 86degrees (POWEL, 2017).

Figure 1: Tower Bridge (Speaker, 2017)

More traffic lights fir the traffic on road and water should be increased for illumination. The regulation that control, the operation of the tower bridge should be added to enable the vehicle not to exceed the weight required for the wellbeing of the bridge. More sensors should be installed to improve the signals. The major forces for the tower bridge are the compression in the pillars and tension in the cables (Speaker, 2017). Because all the forces of the pillars is vertically downward and stabilized by the major cable, the pillars can be made slender. The tower bridge have the open truss structures to support the bed of the road mostly owing to the unfavorable impacts of applying the plate girders. The types of loads that operates at the tower bridge are; live loads, dead loads and dynamic loads. The dead loads is the mass of the bridge itself. The bridge can have a probability of collapsing because of the gravitational forces on the materials used to construct the bridge (Walther, 2013). Live loads are the traffics moving across the bridge as well as the changes in precipitation, temperature and winds. The dynamic loads are the environmental factors that are above the conditions of the weather like sudden earthquakes and wind. All these factors were and the loads types were taken into consideration when the tower bridge was being constructed to prevent it from collapsing (Welch, 2018).

The table below describes the evaluation process of the tower bridge in London. The bridge was found to be very significant since it was constructed. The bridge is capable of serving both the traffic of pedestrians, water vessels, vehicle and other exhibitions (Welch, 2018).

Technical performance measures	The requirements	benchmarks	Relative importance%
Size	244m length, 65mheight, longest span of 83m	Length is 244m, span of 83m and height of 65m	5
Operation	The traffic is more than 40000 daily	Average daily traffic is more than 40000	34
Type of design	Suspension/bascule bridge	Falls under the hydraulic and moveable bridges	15
Maintainability	4 times per month	monthly	20
Time of process	1886 to 1894	8 years	21
Human factors	Less than 10%error rate per year	Less than 8% error rate yearly	5
			100

Conclusion

This research paper was about the hydraulic bridge and the selected named one is the tower bridge which falls under suspension and Bascule Bridge. It is based on the machines that lift the part of the bridge so that it can allow the river traffic under it to pass. The bridge is near the harbor so it was important for it to be designed in the type that can enable the ships to pass. The machines that were replaced by the electro hydraulic drive were left in the museum of the tower bridge to attract the tourists. The bridge comprises of two bridge towers tied together by two horizontal walkways tied together at the upper level constructed to withstand the horizontal forces caused by the suspended section of the bridge on the tower’s landward side. The vertical components of the forces in the section suspended and the vertical reaction in a two walkway are carried by two towers. The bascule pivots and operating machines are housed in the base of every tower. The deck of the bridge is accessible to both vehicles and pedestrians.

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