The Technical University of Vienna (TU Wien) has demonstrated a novel approach to bridge-building in Austria that resembles the opening of an umbrella.
Engineers have shown that a bridge can be unfolded rather than built piece by piece, a technique that the university says does not require scaffolding, and so saves time and money, and has less environmental impact than traditional methods.
The university patented its technique in 2006, and has been refining it ever since.
Its first full-scale demonstration took place over several hours on 27 February when a 116m-long bridge over the River Lafnitz was unfolded.
Professor Johann Kollegger of the Institute of Structural Engineering of TU Wien said: "A variety of bridge building techniques are applied nowadays. If the bridge is not too high it can be erected using scaffolding. Another technique is to erect the bridge pier and work from there in a balanced way in both directions. Sometimes steel girders are constructed and then pushed forward bit by bit in a horizontal position until the span is completed."
In TU Wien’s system, girders are mounted in a vertical position on both sides of a concrete pier and then unfolded, like an umbrella. "The two girders are connected to each other at the top, directly above the pier," Kollegger said. "With hydraulic systems, this joint is then slowly lowered, and the girders unfold to both sides."
"The two girders are connected to each other at the top, directly above the pier," Johann Kollegger of the Institute of Structural Engineering of TU Wien explains. "With hydraulic systems, this joint is then slowly lowered, and the girders unfold to both sides."
Once these hollow girders have been lowered all the way and are horizontal, they can then be filled with concrete to complete the main structural components of the bridge. In the case of the Lafnitz bridge, the girders were 36m long. The gap between these horizontal girders and abutments were filled with suspended girders to complete the bridge. of 100 m (330 ft) in length over the river and 116 m (380 ft) over the Lafnitz.
A video of the unfolding process can be seen below:
The lengthy testing period was required to resolve "many questions" about how best to unfold a bridge, from the metal joints, that have to withstand increased forces during the lowering process, to the hydraulic jacks that are needed to lower the bridge into position.
"Erecting bridges using scaffolding usually takes months," Kollegger said. "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."
Now that the university has demonstrated the advantages of its idea, Kollegger and his colleagues are hopeful that it will become a common bridge-building method.
Image: The unfolding technique on site (TU Wien)