Bailey bridges: What makes them so special

The now-completed Rissington Bailey bridge while under construction. Photo / Warren Buckland

Three months after Cyclone Gabrielle, Bailey bridges are being built in Hawke’s Bay to provide vital lifelines in areas where bridges were washed away.

The bridge was invented by a British engineer named Sir Donald Coleman Bailey.

After graduating from Sheffield University, Bailey worked for a time in railroading but, in 1929, joined the staff of the Experimental Bridging Establishment of the Ministry of Supply.

When World War II broke out, he had already developed an idea for a military bridge and, in late 1940, at a conference on the problem of providing temporary spans capable of taking heavy loading, his concept of a strong, but relatively light steel truss that could be prefabricated in sections, was at once approved.

So, in 1940-41 the Bailey bridge went straight into action for military use during World War II and saw extensive use by British, Canadian, and American military engineering units.

One of the reasons the Bailey bridge became so important was that, from 1941-45, the world’s biggest tanks, such as the 36-tonne “Churchill Tank”, were made and this weight caused a normal bridge to buckle.

Without a bridge that could cope with this weight, the tanks were useless.

A Bailey bridge is similar to a flat-pack piece of furniture - all the pieces fitted into the back of a small service truck and it was light enough to be lifted by six soldiers.

The characteristics of the Bailey bridge are standardisation and simplicity of panels, readiness of assembly in the field, capacity for additional strengthening by doubling or tripling the truss girders, and adaptability to long spans with the aid of pontoons.

Bailey bridges remain a cost-effective system, being versatile, quick, and easy to build and dismantle. With a basic component of a 3-metre-long truss panel, they can be configured to provide much longer spans and cater for a wide range of loads.

A standard 30m bridge could be assembled within a week. Longer-span bridges might take longer owing to the need to build piers to support them.

Progress on bridges

Two Bailey bridges have already been installed in Hawke’s Bay, Waka Kotahi regional manager of maintenance and operations Jaclyn Hankin says in an update - one at Opoiti, north of Wairoa, and the other at Rissington in Hastings district.

“Whether Bailey bridges can be installed, and how quickly they can be set up, depends on how accessible the location is and how much work needs to be done to prepare the site,” she said.

“For example, sometimes piers (the support columns a bridge sits on) might need to be built to support the bridge, which can make installation take longer.

“The Opoiti Bridge was able to be installed in four days, as the site and design of the bridge didn’t require complex works.”

Hankin said both the Opoiti and Rissington bridges were on council-owned roads and Waka Kotahi facilitated their installation.

Work to restore access along cyclone-damaged State Highway 2 between Wairoa and Napier had progressed faster than Waka Kotahi anticipated, she said, with that stretch of road reopened on May 14 and favourable weather “helping to accelerate construction of the Waikare Gorge Bailey bridge”.

Contractors have been working on other damaged sites, including Devil’s Elbow, as well as clearing landslips and debris, to make the road safe.

“Further north on SH35, a 300-tonne crane has been at site to enable construction of the piers and ultimately the bridge across Hikuwai River.”

Realising rural communities had been isolated as a result of Cyclone Gabrielle, Waka Kotahi was in regular communication with them and stakeholders across Tairāwhiti and Hawke’s Bay about the work and tried to cater to residents’ needs as much as possible, Hankin said.

The priority was to “safely and efficiently restore key links and access to these communities”.