An imaginative new approach to bridge-building was demonstrated for the first time in Austria last week, where engineers have connected the opposing sides of two rivers with a novel construction method likened to opening an umbrella.

These unfolding bridges promise a number of benefits over traditional techniques, saving considerable time, money and impact on the local landscape.Generally speaking, bridges are constructed piece by piece through the use of scaffolding, or through piers which act as vertical load-bearing structures as the bridge is carefully built outwards in either direction, bit by bit to keep things balanced.

For more than 15 years, researchers at the Vienna University of Technology (TU Wien) have been working on a different approach, and actually patented the idea way back in 2006. It involves hollow girders mounted to a pier in an upright position, which are joined at the top and and are gently unfolded downwards.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.”