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Department of Civil Engineering
CIVL 3121 - Interesting Information about Structures
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This Is a Completely New, Possibly Perfect Way to Build Bridges


The umbrella-like balanced lift method is brilliant. By Caroline Delbert
Mar 4, 2020

• Structural engineers have built a new bridge using an unfolding, umbrella-like technique.
• The engineers say the process is ideal for unusual terrain and reduces time and cost.
• Hollow steel girders are lowered slowly and steadily into place by a hydraulic lift.


A new kind of bridge construction opens and unfolds like an umbrella, creators say. Structural engineers at the TU Wien, or Vienna University of Technology, have built a prototype bridge mechanism with a central umbrella handle and two opposite spokes controlled by a slider. The example bridge spans a river in Austria.

The umbrella method is a completely new way to construct a static final bridge. This TU Wien team first worked on the idea in 2006, and it’s been experimenting and fine tuning since then. Instead of traditional kinds of bridge building—i.e. putting up long-term scaffolding as rebar is laid and concrete is filled into structures—this mechanism is built like a “closed” umbrella and then unfolded into its final position. From there, its hollow girders are filled with concrete and the rest of the structural elements are completed.

“Erecting bridges using scaffolding usually takes months,” designer Johann Kollegger said in a statement. “The elements for the balanced lowering method, on the other hand, can be set up in two to three days, and the lowering process takes around three hours.” But this process, he says, is less invasive for bridges through protected or uneven terrain. The team's sample bridge over the Lafnitz River touches a nature preserve.

The resulting bridge section has a span of 72 meters (about 236 feet)—enough to span many rivers and highways. Sections can also be daisy-chained and connected into longer bridges. Each girder weighs over 50 tons, and they’re lowered carefully and symmetrically over a pretty long time. Traditionally constructed bridges are also often built out symmetrically, because even small imbalances can break the foundations that have been constructed.

Using hydraulics ensures the heavy girders are lowered at a totally even and steady rate, and once the girders are nestled in place, the hollow steel construction is filled with concrete. Kollegger says the bridges that result from this process are as strong or even stronger than traditional bridges.

It makes intuitive sense, too. Construction with fewer, longer pieces leaves less to chance in the form of joins and other added labor.

There’s one more “horizontal” traditional approach with a similar kind of outcome. Some bridges are constructed by building the vertical supports and then slowly scooting an almost-completed deck across the top. In that case, the surface is made of just one piece that can be fully assembled off to the side or assembled in situ as portions pass through a construction zone before being scooted.

The TU Wien statement doesn’t say this explicitly, but this technique seems like it could improve construction on some of the scariest bridges, like those that go a short distance across an extremely deep ravine, for example. (Think: in the narrow gauge railroads of the high Himalayan Mountains, or the rapidly expanding railroads and highways of southern China.) The perilous-looking, partly completed bridge in Wulong County in Chongqing shows the symmetrical construction method in progress.

Ongoing construction of the Yangshuihu Bridge in southern China.

Imagine if the only moving part here was an autonomous hydraulic lift, after which you’d already have a basically safe and completed bridge ready to fill in and finish. If the science, well, holds up, these projects could take much less time and money and be much safer for workers.



This website was originally developed by Charles Camp for CIVL 3121.
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