It used to be that skyscrapers or natural landscapes (usually those of the New Wonders of the World variety) defined the cityscapes of the world’s most visited cities.
That has changed significantly since 2000 when the London Eye opened in London, England. Suddenly it was an amusement ride that was included in the printed cityscape of every touristy momento sold at gift shops.
In 1893, during the Chicago World’s Fair, America aimed to flex its engineering muscle by building something to rival the Eiffel Tower.
George Washington Ferris was a bridge and tunnel engineer who is credited for conceiving the Ferris Wheel.
Though there’s some evidence it was Ferris’ partner, William Gronau, who worked out the technical specifications for the wheel, Ferris worked his entrepreneurial skills to make it a reality.
Standing at 264 ft. tall, the fair unveiled its Ferris wheel – a structure that towered over the Chicago skyline in 1893.
According to A Short History of Fairs and Ferris Wheels, the wheel’s axle weighed 89,320 pounds.
At the time this was the largest single piece of steel forged and also a precursor for the giant Ferris wheels of today.
The wheel turned atop twin 140 ft. towers erected on top of concrete pedestals that sat on pilings driven over 30 ft. into bedrock.
The construction of the wheel by ironworkers took over 100 days. It opened on 1 May 1893 with 36 cars that could carry 60 passengers. It weighed 26,000 lbs and measured 24 ft long.
Ferris’ great wheel carried three dozen cars that could carry a maximum of 60 passengers each. They weighed 26,000 lbs. and measured 24 ft long, 13 ft wide, and 10 ft high.
The wheel was powered by a chain drive system powered by a 1000 hp reversible steam engine, with a second engine as a backup.
The engineering darling earned an estimated $750,000 USD in roughly four months’ run at the fair.
While showing so much potential after the fair it was moved and its glory soon faded in 1906 it was dismantled and the steel was sold for scrap.
But Ferris Wheels stuck, became smaller, and turned into traveling entertainment that delighted the world.
But it wasn’t until the new millennium when giant wheels became defining pieces of engineering and cityscapes that the London Eye officially opened to the public.
Since opening it has maintained status as the UK’s most popular paid visitor attraction. A remarkable feat of design and engineering, the London Eye gave London’s skyline a dramatic edge and has been offering guests a new perspective on the city.
The wheel also clearly helped define mega structures of this kind and what a Ferris wheel is.
The London Eye is in fact not a true Ferris wheel but rather a cantilevered observation wheel (and the world’s tallest at that). It’s not considered a Ferris wheel because the pods are completely enclosed and climate-controlled, and the pods are positioned on the outside of the wheel structure and are fully motorized individually.
As a third point for clear definition, the entire structure is supported by an A-frame on one side only.
While it may not be considered a true Ferris Wheel the London Eye managed to again show the importance of these structures as tourist attractions, and much like the original wheel in Chicago show the economic value of these giant structures.
The London Eye is an Engineering structure and these facts prove it:
Currently, the highest observation wheel is the High Roller in Las Vegas, America. But other wheels like Singapore Flyer, Star of Nanchang in China, Sky Dream in Taiwan, London Eye, Redhorse Osaka Wheel in Japan, Wheel at Icon Park in Orlando, Melbourne Star in Australia, Zhengzhou Ferris Wheel in China, Changsha Ferris Wheel in China, and the Tianjin Eye in China also joins the list of mega-wheels on earth.
The third tallest Giant Wheel is the Singapore Flyer, located in Singapore.
The paper The Singapore Flyer And Design Of Giant Observation Wheels gives insight into how these mega-structures are designed and ultimately opened to the public.
Singapore Flyer was an engineering-led process that recognized the importance of a number of geometric effects on the efficiency of the structure.
With that in mind, the following considerations were made…
Singapore’s Marina Bay was chosen as an optimal site for a tourist attraction of this kind, and as such specific choices had to be made for the foundations of the wheel.
In this case, marine and fluvial sediments of the Kallang Formation which is unconsolidated to normally consolidated was kept in mind.
The foundations for the wheel are bored piles 600mm and 1500mm in diameter that penetrates 52m deep and in turn socketed into the Old Alluvium.
2. How to build it
Engineers made sure that the wheel is supported by two 2,850mm diameter columns and stabilized at the spindle level by 4 cable stays.
Each cable stay is a group of 6 x 100mm diameter locked coil cables prestressed to 17MN.
The lateral components of the pre-tensions are resolved through spindle structures that connect the tops of the columns as well as the support.
Its stiff closed structural system distributes and balances the other components of the wheel.
The piles of the Singapore Flyer are only required to resist the vertical uplift and downwards reactions of the wheel with considerations made for the lateral force arising from wind loading on the structure.
3. Spoke and rim design
There’re three external load cases that generate forces in the rim and spokes of the wheel.
Gravity causes tension in the lower spokes and compression in the upper ones of the wheel, along with compression in the lower half of the rim and tension in the upper half.
Wind in the area causes tension in spokes attached to the windward side of the wheel and then also temperature creates differentials between the rim and spokes that causes spoke tension and rim compression.
To resolve this the Singapore Flyer uses cable spokes that is prestressed to resist compression. The prestress allows the cables to never go slack, and they always effectively control the displacement of the rim.
Rim bending is minimized in normal operation because of the alignment of cables with capsule supports.
The CHS (circular hollow section) of the wheel measures 864 x 25.4mm chord size – and it allows for an accident condition in which a cable is assumed to break.
This also allows cable replacement if required because the hollow sections allow there not to be a change.
Drewery, Jim. (2015). A Short History of Ferris Wheels.
https://www.londoneye.com/our-company/press/ Allsop, Andrew & Dallard, Pat & McNiven, Brendon. (2009). The Singapore Flyer and Design of Giant Observation Wheels, Singapore. Structural Engineering International. 19. 12-16. 10.2749/101686609787398326