CIVL 3121 - Interesting Information about
Structures
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.