Worlds first long span network arch structure to use Ovako structural steel

DUDLEY, UK – Ovako has won the contract to supply Macalloy with structural steel for the world’s first long span network arch bridge, currently under construction in Prague.

The £29 million Troja Bridge will span the famous River Vltava using the innovative network arch method, which has been described as, ‘a major leap forward in structural efficiency’. Once completed the impressive structure, a key crossing for the important Prague ring road, will span 200.4 metres and have a total width of 34.4 metres. It will carry a four lane dual carriageway, twin tram tracks along with pedestrian and cycle paths.

“We have been working on securing this order for some time,” explained Peter Hoy, Managing Director of Macalloy Limited, “liaising closely with Ovako on the technical specification, material grade, size requirements and scheduling of deliveries, all of which are critical to the success of such a project. It is the culmination of an extensive research and development programme on the innovative, network arch technique by designers Mott MacDonald.

“Throughout Europe we see a lot of the bowstring bridge designs and are able to supply the finished suspension bars ready for installation and tensioning on the bridges in question. This is a first for the network arch design. Efficiencies in this method of configuration of the arch and the way the bridge works are driving further efficiencies in the construction process,” explained Peter Hoy.

A traditional bowstring arch would have to be over 50 metres above the bridge deck, however, using the network arch method with the diagonal steel system the overall height of the arch will be reduced to 20 metres.

Structurally efficient, the technique uses the steel suspension bars in a diagonally rather than vertical configuration. They stiffen the bridge and spread the loads from the deck across a larger area of the arch, allowing major design efficiencies to be introduced.

“Our ability to produce structural steel of this nature for bridge applications is well known,” said Richard Bloor of Ovako, “with our material installed on many state-of-the-art bridges and structures throughout the world. We are particularly proud to win this order from Macalloy for the Troja Bridge being the first long span network arch project of its type.

“Working closely with customers from the outset of a project on the technical detail and specification of the micro-alloy steel grade, in order to produce the ideal yield and tensile strength, is critical and produced the ideal solution for this application.”

Supply of the material has commenced from Ovako’s Smedjebacken plant in Sweden direct to Macalloy in Sheffield where the bars, which range from 2 metres to 12 metres depending on their location on the structure, are trued, an exact thread is applied over the diameter and a protective finish is added. They are then shipped to the company’s distributor, Tension Systems in the Czech Republic, who are carrying out the installation.

Construction on the project commenced in 2010 and the Troja Bridge is due for completion in autumn.