The SourceCivil Engineering MagazineThe Victoria Falls Bridge holds its own against a natural wonder
History Lesson

The Victoria Falls Bridge holds its own against a natural wonder

By T.R. Witcher

It was called a “poem in steel” by the Times of London. Steel was shipped halfway around the world to build it. It was a marker of imperial ambition in Africa but now connects modern Zambia and Zimbabwe. Situated adjacent to one of the world’s most stunning natural wonders, the Victoria Falls Bridge soars 420 ft above the Zambezi River, just downstream from Victoria Falls itself.

Located in southern Africa, Victoria Falls is among the largest in the world — a sheet of water nearly a mile in width and falling twice the height of Niagara Falls. Peter Roberts, in his 2020 book, Sun, Steel and Spray: A History of the Victoria Falls Bridge, quotes writer Mark Strage, who described the challenge of building a bridge there “supported by a single slender span” as “bold, to the point of arrogance.”

The falls area was home for centuries to the Toka-Leya people, who ascribed cultural and religious significance to the churning waters at the foot of the falls. Their name for the falls alternately translates as both “the mist that thunders” and the “place of the rainbow.”

The first European explorer to see the falls was Scottish missionary and explorer David Livingstone, in 1855. “I did not comprehend it until, creeping with awe to the verge, I peered down into a large rent which had been made from bank to bank of the broad (Zambezi),” he wrote in his journal, which was later published in his 1857 book Missionary Travels and Researches in South Africa. He declared it to be “the most wonderful sight I had witnessed in Africa.”

Livingstone traveled 3,000 mi within Africa and published his best-selling book about the trip afterward, while in England. He saw the Zambezi as the route “by which the central regions of Africa would be opened up to Christian values and trade.” 

But the driving force behind the bridge was Cecil John Rhodes, who founded diamond producer de Beers Consolidated Mining Company in 1888. Beginning in 1890, Rhodes served six years as the prime minister of the British Cape Colony (now South Africa). He was, wrote Roberts, “an ardent believer in British colonial imperialism” and saw the potential of a transportation route linking the entire continent north to south. 

Rhodes helped the British Empire seize control of southern Africa, founding the large territory that for decades bore his name, Rhodesia, in 1895. (Rhodesia essentially encompassed what is now Zambia, north of the Zambezi, and Zimbabwe, south of the river.) Rhodes allegedly once told a friend that “to have a bit of country named after one is one of the things a man might be proud of,” according to Roberts, who quotes the historian Robert Rotberg from his book The Founder: Cecil Rhodes and the Pursuit of Power.

The push to establish a transit route from the Cape to Cairo came in the midst of a European land grab in Africa that included moves by the Portuguese and the Germans. Although the full route never materialized, Roberts wrote, “this period saw the rapid spread of an interconnected web of ‘pioneer railways,’ penetrating the subcontinent from the south and east coasts and opening up the interior to development.”

Rhodes never actually saw the falls before he died in 1902, but he had dreamed of and approved the siting of a rail bridge close enough to the falls so that passengers would be able to enjoy “the spray of the water over the carriages.” The men put in charge of realizing Rhodes’ vision were civil engineer George Andrew Hobson and 27-year-old French engineer Georges Camille Imbault. Imbault was appointed chief construction engineer by Cleveland Bridge and Engineering Co., the British firm that manufactured the bridge components.

There was plenty of opposition in Africa and England to constructing the bridge so close to the falls; many were concerned that a piece of infrastructure would forever ruin such a magnificent landscape, and some maintained that an alternate site several miles upstream would have been an easier crossing. But Hobson defended the plan for a bridge near the river, claiming the alternate site would result in an unimpressive structure. The final choice, just downstream from the falls, “was governed by the natural formation of the rock walls of the Batoka Gorge, advantage being taken of the minimum distance to be spanned, combined with the soundest foundations obtainable,” Roberts wrote.

Rhodes’ rail line had reached the town of Bulawayo, about 269 mi southeast of the falls, in 1897. Between 1902 and 1904 the line finally reached the bridge site near the falls, a landscape teeming with antelope, elephants, giraffes, and lions — and passing, Roberts wrote, through “sand veld, well wooded with mopane and teak.”

According to Hobson, the priorities for the design included a handsome appearance, rigidity, economy, and ease of building without scaffolding. “A steel arch of this character was therefore designed to spring from the rock walls of the Zambezi chasm, to be erected cantilever-wise simultaneously from both sides” (“The Victoria Falls Bridge,” Minutes of the Proceedings of the Institution of Civil Engineers, March 19, 1907).

The final design featured a 500 ft long main arch with a rise of 90 ft, anchored by four touch points called feet on the steep banks of the gorge. The design called for two support spans embedded near the top of the gorge  — one with a length of 62.5 ft on the left bank and one with a length of 87.5 ft on the right.

Hobson noted that a three-hinged arch design was considered but ultimately rejected for “want of rigidity under railway-traffic.” He wrote that designers felt “great uneasiness” about the three-hinged option because “excessive longitudinal vibration” might develop “under traffic at even moderate speeds.” He acknowledged that calculating the stresses for a two-hinged design was more challenging, but ultimately the option was both more rigid and more economical.

There was also the matter of preserving the steelwork, given its proximity to the water spray from the falls and the “comparatively slight” wind bracing of the structure. Roberts noted that engineers strove for simplicity in the design of the bridge sections to avoid “enclosed parts or hidden spaces anywhere in the structure” that might lead to corrosion. “There are no cavities for holding water, nor any surfaces where moisture can condense, the air being free to circulate everywhere.”

The bridge components, made of rolled steel, were not fabricated on the remote site but rather in England by Cleveland. The steel sections were built in a factory in Middlesbrough, then shipped 9,500 mi to the Port of Beira in present-day Mozambique. From there, the pieces traveled by train to Bulawayo and then on to the falls.

Before being shipped off, the steel components were cleaned and treated with a red lead primer and linseed oil then painted with three coats of silver-gray paint. “This particular shade was chosen because a patch of rust in it will appear conspicuous by contrast,” wrote Hobson. “It has the further advantage of absorbing little of the heat of the sun. Thus painted, the steelwork, a year and a half after completion, was reported to be in very good condition, and to respond slowly to changes of temperature.” The color was also expected to blend in well with the falls. 

But before construction began, engineers realized they had made a critical error in their initial surveys. According to Hobson, the north bank of the gorge was “an almost perpendicular cliff, but the opposite bank has a shelf about half way up, and the whole region is composed of erupted rock, mostly basalt.” He wrote that the bridge “was designed to fit the profile of the gorge with as little expenditure on excavation as possible” because the rock in the gorge was thought to be very hard. But the rock on the shelf of the south face was actually “covered to a considerable depth with debris” and was unsuitable to build on unless it was cleared. 

At the time of this discovery, progress on manufacturing the steelwork was too far along for anything in the design to be changed. “The difficulty had therefore to be overcome partly by increasing the depth of the concrete foundations, and partly by lowering the level of the entire bridge to the extent of 21 feet,” Hobson wrote.

As work at the site got underway, the bridge’s assistant resident engineer, Charles Beresford Fox, designed a winch system to carry workers across the river on a bosun’s chair. Workers would sit in the chair, which was attached by pulleys to a ⅝ in. wire rope. The rope was supported on each side of the gorge by 2 ft diameter posts that were sunk 7 to 8 ft into the rock.

Rhodes’ dreams of an empire may not have lasted, but the Victoria Falls Bridge certainly has, bringing the falls’ majestic sprays of water closer to millions. 

Fox took the first safe but somewhat harrowing ride, noting that it felt strange to be “relying absolutely on my own calculations for my safety,” according to the website of the Zambezi Book Co. The website also refers to him as the “Flying Fox” and says he was “the first man to cross the gorge; the first man to descend into the gorge from the southern bank — and, subsequently, the first man to be rescued from the gorge.” Ultimately, though, the bosun’s chair saved work crews hours versus having to transport material by ferry.

Eventually, construction material was transported across the gorge by an electric system nicknamed the Blondin, after French tightrope walker Charles Blondin, who famously crossed the gorge at Niagara Falls. The Blondin, Roberts wrote, “travelled along a single cableway over 870 ft in length, fixed to a tower on the north bank and hinged sheer-legs on the south bank.” The system was “designed to counter the weight of the machine as it moved along the cable.” The Blondin could lift loads up to 10 tons at a speed of 20 ft per minute and travel along the cable at a speed of 300 ft per minute.

The keys to the bridge’s design were the four feet, two on each side of the canyon where the main arches joined the canyon side. These feet were hinged by steel pin bearings and mounted to concrete abutments. According to Roberts, the steelwork of the arch was designed to expand and lift a bit under the heat of the sun, “but at the same time retaining its rigidity without buckling or becoming distorted.”

To build the main arches, two mechanical cranes traveled along the cross girders of the half-arches, moving forward to install each of the 20 panels that would form the main arch. “In order to support the cantilevers as they stretched over the gorge, a system of steel wire cables was used, anchored through tunnels cut into the rock on either side of the gorge,” Roberts wrote. “Two bore-holes were sunk back from the edge on each bank 30 ft deep and 30 ft apart, and joined underground by boring a tunnel through the rock. Wire ropes suspending the weight of each half of the bridge were passed down one hole, along the connecting passage, and out through the other hole, so that the weight was sustained by this solid mass of rock.” Five hundred tons of rail was placed on top of the rock for added stability. The tension of the cables could be adjusted, wrote Roberts, to allow “precise control and adjustment of the half-arches as they were erected.”

The arch halves were finally joined on April 1, 1905. “With the lower arch now connected, work progressed to fix the upper chord in place and complete the steelwork structure,” Roberts explained. “As the horizontal chord neared completion two hydraulic jacks were inserted into the small gaps between either arm of the arch, exerting between them a permanent pressure of 500 tons outwards… .” This pressure forced the gap open and allowed the final section to be fitted into place.

Over the years the bridge has received periodic maintenance and refurbishment.

The upper deck was completed in June 1905. Apparently, the first creature to cross the bridge was a leopard. A few months later, on Sept. 12, the bridge officially opened to rail traffic.

Over the years the bridge has received periodic maintenance and refurbishment. The deck was reconstructed and strengthened in 1929 to fix a structural deficiency in the original design. Roberts writes that the original deck consisted of cross girders spaced 12 ft, 6 in. apart, which placed a heavy load midway between the panel points of the bridge. This, in turn, introduced a bending load on the top chord of the arch. In the new deck, the cross girders were spaced further apart to line up with each panel point. This required a much deeper girder, which raised the rail level by 4 ft, 7 in.

In the years after the bridge opened, Victoria Falls slowly became a tourist attraction and place of intrigue. In 1939, on the eve of World War II, a German saboteur was arrested for plotting to destroy the bridge. Engineers found a hole had been drilled into one of the support beams that was large enough to stuff with explosives. 

In later years, Rhodesia would eventually give way to modern Zambia, which achieved independence in 1964, and Zimbabwe, which achieved independence in 1980, the river and falls between the two.

The bridge has periodically been repainted and renovated. It was closed in 2006 for a thorough examination of its structural integrity and was found to be in generally good shape. A $1.7 million rehabilitation strengthened its sustaining load capacity from 46 tons to 56 tons. In 1995 it was named an ASCE Historic Civil Engineering Landmark.

Rhodes’ dreams of an empire may not have lasted, but the Victoria Falls Bridge certainly has, bringing the falls’ majestic sprays of water closer to millions. 

This article first appeared in the July/August 2021 issue of Civil Engineering as “A Poem in Steel: The Victoria Falls Bridge.” 

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