Serge Montens, Chief of Bridge Division, Systra Paris, France
Transportation needs are increasing very much in developing countries. Both urban and inter-cities transportation infrastructures are being developed very fast for highways and railways. Light rail transit systems are often carried by viaducts, which are more economical than tunnels.
As a consequence, the number and the length of new long bridges are increasing more than ever. In order to build these long structures in a reasonable amount of time, new construction methods have to be imagined. Many long viaduct decks are made from precast segments, 3 to 4m long, assembled using self- moving steel beam. For very long viaducts, this method requires giant precasting yards, as for Dubai metro. This construction method allows assembling a typical 30m span in 2 to 3 days. But this method, although faster than cast-in-place construction, is not sufficiently fast to build very long viaducts in a reasonable amount of time.
The logical solution is to increase the size of the segments, in order to decrease their number, and then the assembling time. We will show some examples of precast full spans, used for highway or railway long viaducts. In that case, pre-tensioning is more interesting than post-tensioning.