Motion is a vastly important aspect of any work of civil engineering. From oscillations to thermal expansion to moving parts such as elevators, many dynamic forces on top of static ones continuously flex and contort structures, breathing life into even the most solid-looking of edifices. For an entire work to be designed to undergo major transformative motion is, however, relatively rare. The most common of these cases, which involve far more mechanical expertise than the average project, are bridges that need to allow large boats beneath them; draw, lift, or transporter bridges like these can be found globally. Near Edinburgh, however, something completely different can be found, an animated fabrication that is completely unique in concept and mechanism. This is Scotland’s Falkirk Wheel, which I was able to see in action earlier this summer.
One of the gondolas from below
The wheel had its genesis in the nineties, when a smorgasbord of new developments and infrastructure was planned to mark the year 2000. One such project was the Millennium Link, a complete overhaul of the canals between Glasgow and Edinburgh in order to recreate the Victorian-era water link between the cities. This involved repairing almost every bridge and lock on the two waterways. The Falkirk Wheel was the endeavour’s pièce de résistance. The brief was to create, in the spirit of nineteenth-century engineers like Paxton and Brunel, a functional landmark, a creative method of raising boats thirty meters that was faster than locks and would also draw tourists. The team, led by architect Tom Kettle, civil engineers Arup and mechanical engineers Butterley, finalized the design in 1999.
The gear train that keeps the gondolas upright
There are a few other canal lifts scattered throughout Europe, but none are rotating devices like the one at Falkirk. Two water-filled gondolas spin around a horizontal axle, reversing their positions in the upper and lower canal in a matter of minutes. The wheel’s design provides a delightful contrast: from a distance it is gracefully sculpted, sleekly clad in gray and white with its horned “arms” resembling the blades of a Celtic axe; up close, however, the oversized mechanical systems are exposed, as on industrial machinery. Most prominent is the gear chain that enables the rings that support the gondolas to remain upright as the structure revolves. Simple but inspired, this system allows much smoother operation than if the gondolas were stabilized by gravity alone. Also visible across the surface are the fifteen thousand bolts used to keep the wheel intact during motion.
Bogies allow each gondola to rotate in respect to the arms
When fully loaded, the wheel as a whole weighs 1,800 tonnes. Despite this tremendous load, only 22.5 kilowatts of power are needed to run the hydraulic motors which power the wheel- a fraction of what is needed to operate an average family car. This feat is the result of a very simple principle: the gondolas and wheel arms are always balanced across the axle, meaning as one lowers, it raises its counterpart with little mechanical assistance. The challenge that the engineers faced was maintaining this balance- keeping the weights of the gondolas equal. In the end, they achieved this task through another very simple principle: that of displacement. Before any boats enter the gondolas, they are filled to a certain water level, beyond which excess liquid drains out. When the boats enter, they displace their weight in water, which exits the compartment. Even if one of the gondolas is empty, enough water will drain in the other to match its mass.
Pillars support an aqueduct which carries the Union Canal to the wheel
The wheel’s main proponents can certainly look back on its inception as a “eureka” moment, for the structure has been a roaring success. Drawing 400,000 visitors annually, it has become a symbol of 21st century Scotland. Upon visiting the wheel, it was immediately clear to me that this popularity was well-earned. Watching the overshadowing construction with its steel and concrete curves gently glide through the air was nothing short of awe-inspiring; I imagine the very first modern steam engine, upon hissing into life, conjured a similar effect on its Georgian observers. The wheel was also reminiscent of images from science fiction, such as the spinning spaceship of 2001. It is a pinnacle of engineering achievement and advancement, and I hope its designers and others continue to dream up such astonishing structures.
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