How to arch a bridge through the spray

16 Mar, 2018 - 00:03 0 Views
How to arch a bridge through the spray The heyday of the bridge: Spray reaches the train crossing the bridge

eBusiness Weekly

Why build a bridge at Victoria Falls?
Cecil Rhodes’ grandiose dream of a railway line linking the Cape to Cairo was well in hand by 1898, fuelled by investment and speculation about the potential of central Africa.By the time the economic decision had been made in 1898 to route the railway via the Hwange coalfields, the tourist potential of the Victoria Falls had already begun to be realised.

A regular wagon service was already in operation, inspiring Rhodes to demand the “spray of the falls over the train carriages,” even though he never visited the falls and died before construction of the Bridge even began.

Such was his influence that his wishes were carried out despite there being a much easier crossing of the river up beyond Kandahar Island.

The railway line reached the Falls on April 24, 1904 under the supervision of railway maestro George Pauling.

He was not to build the bridge but his daughter, Blanche did drive the last lap to Victoria Falls, the locomotive flying a Union Jack and bearing a board reading “We’ve got a long way to go”, referring to Cairo.

So who was in charge?
The survey of the bridge site was made during the Boer War of 1899-1902, and in May 1903 the contract was given, despite keen foreign competition, to a British concern, the Cleveland Bridge and Engineering Company, of Darlington, County Durham.

This firm also built the Lower Zambezi Bridge at Sena, Mozambique and with a total length of 4.4 km it is the longest bridge in Africa.

Pauling writes in his autobiography about his disappointment at not getting the contact to build a world monument: “My firm had sent in a tender but it was too high; their tender, on the other hand, was too low, and I hardly think they made a profit on the work.

I had had so great a connection with railway work in Rhodesia that I was sorry we had not the honour of building the bridge, but honour of that kind can be purchased at too heavy a price”.

The winning tender was for £72,000; in 2008, The Property Gazette estimated that US$32 mln would be needed to replace the Bridge, while today the Infrastructure Development Bank of Zimbabwe set a high level estimate cost of US$50 million.

Who designed the bridge?
The bridge was actually designed by G.A. Hobson but the preliminary calculations were made by Ralph Freeman. He would rise to fame as the designer of the Sydney Harbour Bridge (1932).

He also designed Birchenough Bridge (1935), which is really a smaller replica of the Sydney Bridge.

His son, also named Ralph later designed the 320m-span steel Otto Beit suspension bridge across the Zambesi at Chirundu; the UK Independent in an 1998 obituary wrongly claimed he designed Birchenough Bridge but he might have worked with his father.

A Frenchman, Georges C. Imbault was the contractor’s agent in charge of the erection and, being unusually enlightened for the time, he later removed all traces of construction debris in deference to the beauty of the area.

How did construction initially proceed?
In about October 1903 the two cliffs of the gorge were linked. First a rocket with a fine string was fired, and on the third attempt the string reached the other side. This enabled a cord to be pulled across, then a wire and finally a cable, carried on supports and tensioned.

By means of a bosun’s chair one person at a time could cross. Once settled a Blondin overhead carrier was constructed.

Named for the famous tightrope walker, Charles Blondin, this consisted of 19 steel wires surrounding a hemp core, with a circumference of 22 cm, a breaking strain of 270 tons and a load limit of 10 tones.

It was operated electrically, carrying its own driver and power lines from a generating station on the cliff top. Despite many difficulties the cable and conveyer lasted for the duration of the job.

All the material for the northern half of the bridge was carried along the cable including many kilometres of rails, thousands of sleepers, contractors’ locomotive and wagons, some 15,000 tonnes in all.

When the atmosphere was highly charged with electricity the conveyer would sometimes be enveloped, high over the gorge, in a blaze of lightning.

What was the final design?
A single-span steel arch was chosen as meeting all requirements. This is of the two-hinged type with its four “feet” hinged to steel bearings in the concrete abutments.

As the sun blazes down, the steelwork of the great arch expands and lifts slightly, turning on its hinged bearings, but at the same time retaining its rigidity without buckling or becoming distorted.

The bridge is of the braced spandrel type; that is to say, there is an approximately horizontal top chord that is linked by verticals to the lower chord or arc.

The panels so formed are braced diagonally and thus the top chord, carrying the load, relieves the arc of some of the stress.

This type of bridge is one of the easiest to erect and every part assists in the building of the whole structure.

How did the bridge’s construction proceed?
The bridge, containing a total of 1868 tonnes of steel, was first assembled in sections at the works in Darlington and then taken to pieces for shipment to Beira; thus the actual erection only took nine weeks while the whole job was done in 14 months.

There were “challenges” on the southern side as suitable rock for the foundations was reached at a lower than expected level, with the result that the bridge was not built on the intended level with the lip of the falls.

This accounts for the rock cutting approach at the northern end of the bridge onto which you suddenly emerge with a wonderful and dramatic view as a passenger.

Only one death was recorded during construction (one source claims two) and the safety net below was never needed.

On April 1, 1905 the lower boom of the arch was linked, soon followed by that of the upper boom with a temporary track laid across the bare girders.

The booms were bolted together in the early morning before the heat of the day would cause the metal to expand.

The shunting engine Jack Tar was used to push lightly loaded trucks to re-supply railway line construction in Zambia; this engine can be seen today in the Bulawayo Railway Museum.

The line reached the administrative capital, Kalomo, in May and railway traffic was opened between the Falls and Kalomo in July 1905.

Did they have an opening ceremony?
The Victoria Falls Bridge was officially opened on September 12, 1905. The opening was performed by Professor George Darwin, son of Charles Darwin and leader of the British Association for the Advancement of Science group touring Southern Rhodesia at the time.

In his speech, Darwin quoted a remarkable poetical prophecy made by his great-grandfather, Erasmus Darwin in 1785:

Soon shall thy arm unconquered steam, afar Urge the slow barge and draw the flying car.

The professor then touched a button which fused a cord stretched across the width of the bridge, after which the first train, which had halted in the middle of the bridge for passengers to alight for the ceremony, slowly drew forward amid cheers.

One of the newest engines in the country at the time, No 54, decorated with flags, palm leaves and other vegetation, pulled the coaches; Allan Bowes was the driver.

What did the scientists think?
There being scientists in the opening party, an experiment to determine how far beneath lay the flowing river was proposed.

One professor is said to have held a stone and his watch, one in each hand, with the idea that he would drop the stone and time its fall. Unfortunately he dropped his watch instead of the stone.

For the record the lower boom of the bridge is about 106m above the swirling water; when it was built, the Victoria Falls bridge was the highest of its kind anywhere in the world.

The event was also celebrated with a special set of postage stamps depicting the Victoria Falls.

How was the bridge used?
As built, the bridge had two railway lines but no road. The idea was that the trains would use each line at different times, easing the strain on the bridge.

Road vehicles — which were uncommon visitors — had to pay the railway (which via the BSA Copmany meant Cecil Rhodes) to be transported over the river, or use the old drift upstream from the Victoria Falls.

In fact, A Guide to Rhodesia (published by the Beira and Mashonaland and Rhodesia Railways in 1924) states that the only practicable way of reaching the Victoria Falls was by rail.

From 1910 a local passenger train ran from Livingstone to Victoria Falls on Saturdays and Sundays.

The Victoria Falls Bridge was strategically important during World War I, primarily because the South African and Rhodesian forces were in action in Tanganyika and this bridge was the only crossing over the Zambezi River.

Following a suspected act of attempted sabotage the bridge was defended with a guard and a portable searchlight.

The bridge was also placed under guard during the Second World War.

In 1929-1930 the bridge was widened to permit road traffic and one of the two rail tracks was removed.

This modification involved widening the surface by just 4m to carry the road and sidewalks, and the bridge floor was raised over a metre in height, the work being done by the Cleveland Bridge Co, which had built the structure.

For more than 50 years the bridge was crossed regularly by passenger trains as part of the principal route between the then Northern Rhodesia, southern Africa and Europe.

Freight trains carried mainly copper ore (later, copper ingots) and timber out of Zambia, and coal into the country.

Didn’t we have politicians perched there once?
In early 1975 in a fresh bid at achieving unity within their ranks the Rhodesian ANC consulted with the leaders of the Frontline States who helped arrange a meeting to plan a constitutional conference for the country and thus end the escalating civil war.

On August 25, 1975 the talks, supervised by SA Prime Minister B.J. Vorster, took place with the Rhodesian Government aboard a South African Railways coach in the middle of the Bridge.

The Rhodesian delegation sat in home territory while the ANC sat on the Zambian side. According to the Herald, the bar service was liberal and two members became intoxicated and disruptive helping the talks to continue throughout the day.

The talks fell through because of the intransigence of all the participants.

What impact did the bridge have on the area?
The arrival of the railway provoked fantasies about the rapid development of the area as a manufacturing centre due to the proximity of large coal deposits and other minerals and its location on a crucial route to the interior.

During and after the bridge’s construction a great deal of scientific work was done on the geology, flora and fauna of the area, in part to better serve the growing tourist industry.

Tourism became the raison d’ętre for the burgeoning town, pushed in part by the easier accessibility facilitated by the railway line. But Livingstone still  remained the main centre for tourism  on both sides of the river until the break-up of the Federation and Zambian independence finally ended the single administration under the British Empire and Federation.

The tourist industry also had dramatic effects on land ownership in the area as more entrepreneurs scrambled to build hotels and other facilities for the visitors.

More seriously, and because of the tourist trade the local Leya people had their access to what was one of their most important religious centres curtailed and abused by the early settlers on both sides of the river. This continues to this day although claims and counter-claims are growing in volume.

Any work done recently?
The bridge is usually repainted every 6-8 years, using 7 200 litres of paint. In 2005, with the support of World Bank funding, Emerged Railway Properties contracted Ramboll, a Danish firm, to carry out at strength assessment to determine the remaining lifespan of the bridge.

They found the bridge to be of generally sound condition and design, and concluded that with the correct and timely maintenance and minor upgrades, the lifespan of the bridge could be easily extended for another century.

The bridge was then closed to heavy traffic for a year, because as the NRZ noted, there were excessive vibrations whenever a heavy truck crossed the bridge.

Following US$1.6 million worth of repairs, the bridge reopened to heavy traffic in June 2006 and could sustain loads of up to 56 tonnes for the next five years while further repairs are being implemented.

What about today?
The bridge itself — today jointly owned by the Zimbabwe and Zambia governments through the Emerged Railway Properties (ERP) — is a gateway to trade between the two states; it remains the only rail link between the two countries.

It has exceeded its lifespan and nascent plans are being mooted to reinforce or replace it. This would be unlikely without external investment.

One could argue that total replacement may be unnecessary, as with the completion of the new Kazungula Bridge in March 2019, the Victoria Falls Bridge could be closed to heavy traffic and form the nexus of a one-stop border post dedicated purely to tourists and light vehicles.

For now, the bridge remains an important part of the tourist trade, providing 111m of pure adrenaline rush!

The bungee jump from the bridge has a near-100 percent safety record; and over 150,000 people have committed themselves to the thrill of jumping off the bridge since the service began in 1993.

You need to be a minimum of 14 years old, average weight, with US$160 (US$115 in 2009) in your pocket to experience the bridge as the builders or pioneer inhabitants never intended but would have probably appreciated.

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