Queen's University Belfast to create world's largest flat-pack bridge

A FlexiArch bridge being installed at Pleasington Golf Club in Blackburn, UK (Photo: Emma Martin, Story Contracting)

Flatpack furniture is one thing, but flatpack bridges? That may seem like reaching, but over 50 of them been constructed in the UK and Ireland, and civil engineers at Queen's University Belfast announce that work will soon begin on the world's longest flatpack arch bridge.

The arch is one of the greatest engineering achievements of human history. Perfected over 2,000 years ago by the Romans, there are examples in bridges and buildings all over Europe that date back almost as long. However, stone arches aren't easy to build. They need skilled masons, special forms made out of wood or steel, and a lot of patience. Even modern arch bridges made out of poured or pre-stressed concrete require a lot of time and labor to construct.

That changed when Professor Adrian Long of Queen's University Belfast invented the FlexiArch system. Developed over 10 years in collaboration with the Macrete Ireland concrete company, it maintains the principle of the Roman arch while greatly simplifying its construction. In the conventional technique, tapered blocks are cemented together on a form, but the FlexiArch uses precast one-meter blocks set in lengths and backed with a flexible polymeric membrane.

The result of this is that the arch rings lie flat on the truck beds that transport them to the building site. A crane with a specially designed lifting bar picks up the rings, which fold under their own length to form an arch – each segment locking against its neighbor. The arch is set into place, secured, and then concrete infilling, roadway finishing, and leveling are added. According to Queen's University, the bridge arches take only four to eight hours to erect instead of months.

The latest and largest version of the FlexiArch bridge will be installed over Wallington River in Waterlooville, Hampshire, outside of Portsmouth. Made of 17 one-meter wide units of precast concrete, it will span 16 m (53 ft) and take less than a day to construct the arches using a 200 - 300 ton (220 - 330 US ton) crane.

"This innovative system is exceptional as it is easily transported in flat pack form and then rapidly installed on site," says Macrete project manager, Abhey Gupta. "It is also unique as its strength does not depend on corrodible reinforcement, thus it should have a lifetime of at least 300 years whereas conventional bridges seldom achieve their design life of 120 years."

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