The late 19th century was an incredibly exciting time for bridge design—and a terrifying one, as engineers tested new ideas at huge scales. Nowadays, most of us don't think very much about the forces at work in the bridges we drive or walk over; they're a banal part of our daily landscape.
The engineers at NEY + Partners, a Belgian structural engineering firm, are stirring up a little of that 19th-century thrill and nodding to some of its most famous structures, too. Earlier this year, the firm won an international competition to design a footbridge connecting the mainland UK with a remote, medieval-era castle on the high cliffs of the Cornish coastline.
The jury called NEY's design "daring" and "very exciting," two words you rarely want to hear in conjunction with a 230-foot-wide footbridge over a gaping chasm on the storm-plagued Celtic sea. NEY's design, at first glance, looks like a delicate steel cantilever bridge—hardly terrifying. But a closer look reveals that at the very middle of the narrow span is a gap: the central joint, connecting the mainland and the island, has been intentionally removed. Essentially, the design calls for two distinct structures, not one bridge; two 115-foot steel cantilevers that almost meet in the middle, but don't.
As it turns out, the same basic idea has been around since the mid-1880s, when engineers began experimenting with cantilever bridges that, of course, did meet in the middle. The British engineer Benjamin Baker designed his famous Firth of Forth Bridge, the largest cantilever bridge of its kind, demonstrating the basic concept with a a now-iconic image of two men supporting the weight of a third in the middle.
"The building conditions were the same," says NEY project engineer Matthieu Mallié of Baker's the 126-year-old bridge and his own footbridge, though he admits that removing the final, central joint doesn't have much precedent. "But, as far as we know, the remaining gap, where the two cantilevers reach each other in the middle, has always been closed. The 'poetic key' was precisely to leave it open."
The point of the joint isn't to terrify visitors—okay, that might be part of the point—but to underline the experience of visiting Tintagel Island, upon which the ruins of a 13th-century castle remain. The bridge is part of a project to make the island itself more accessible to tourists. Tintagel is steeped in history: It's been described as the mythical site where King Arthur was conceived, and more concretely, it was the seat of power for medieval rulers: "Modern archaeologists believe Tintagel to have been the seasonal seat of Cornwall and Devon’s (Dumnonia’s) Dark-Age rulers as well as a key trading settlement, which formed a unique link with the Byzantine world," the competition organizers explain.
So the gap isn't just a gimmick, it's a nod to the passage between old and new. For now, Mallié says the design process is only beginning, and the firm is researching the maximum width legally allowable for the gap—likely about two inches—and construction methods. "Walking over the gap, however it will finally look, has to be the climax of the crossing," Mallié writes. "Visitors should feel that 'something' is happening. We believe that it will be a very enjoyable experience."
All Photos: via NEY + Partners