Last week, we looked at the Institution of Structural Engineers' picks for the best structures of the year. But its annual Structural Awards also has a bridge-only category, the shortlist of which is a great survey of the state of the art in bridge design.
In some ways, bridge design is far more experimental than any other. The race to build further, faster, for less is still driving incredible innovations in the field, just like it did at the dawn of the suspension bridge in the 19th century. Below, take a look at five of the nominees for the highway and railway bridge category and the designs that help them defy gravity.
The Second Penang Bridge
Building the longest sea crossing in Southeast Asia -- 24km! -- required some pretty unusual engineering. The China Highway Planning and Design Institute designed a system that required boring piles more than 90m into the bedrock below the ocean floor. Those piles, as you might expect, are heavy duty. In the deepest sections of water, they can grow up to more than 1.5m in diameter of tubular steel, and some of them end up being over 127m long.
The unusual edges of this bridge in Hamburg, designed by Buro Happold and architects Wilkinson Eyre, are actually cantilevered over the rest of the bridge, adding extra space for bikes and foot traffic. The bridge itself uses something called an "orthotropic deck," which means the deck of the bridge itself is stiff enough to actually play a roll in the structural profile of the bridge and support vertical weight -- a feature that's becoming more and more common in bridges.
But maybe the coolest part? At the very middle of the bridge, there's a 30m wide chunk that can actually be removed. It's not a draw bridge -- no, this piece is made to be removable in case there's ever an especially tall ship that needs to pass in the future. Talk about good planning.
Waschmühl Valley Bridge
This bridge was actually an addition to a historic brick arch that carries a highway. To give it more strength, Leonhardt, Andrä und Partner played Dr. Frankenstein to the original arch structure. On top of the simple structure, they created a steel deck bolstered by the cables you see above.
This is called an "extradosed" bridge, a type of structure that's gotten more and more common over the past two decades. Extradosed bridges are hybrids: They use both a box girder (in essence, a column that supports from the ground) and cables, which means that the bridge will often use less material and require less work to keep afloat. In this case, extradosed was a perfect choice for aesthetic reasons: The lower, simpler cable-stayed elements and the thin box girder perfectly underscore the original bridge.
This 3,700-foot long bridge over the Elber River, engineered by Leonhardt, Andrä und Partner, is an exercise in simplicity. Rather than a symphony of systems that work together, it relies on a single, efficient structure: A tall, steel and concrete tower that anchors the cables that keep the deck itself in place. According to the jury, the sheer simplicity of it makes it beautiful. It's "thoughtfully detailed to fit perfectly into the surrounding landscape whilst, at the same time, creating a landmark structure."
Shenyang Hun River Ribbon Bridge
This bridge in Shenyang, China, is interesting because unless you're driving or walking across it, it's hard to see the structural acrobatics going on along its length. See those looping arches on its edges? These are steel arches that actually tilt inward at a crazily steep 17 degrees. What's more, only one of them, at nearly 400 feet wide, connects at the center for extra support. They're supposed to resemble "streamers dancing gracefully and dynamically above the water," according to the jury.