The Structural Engineer > Archive > Volume 83 (2005) > Issues > Issue 4 > Modern composite bridges in Germany
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Modern composite bridges in Germany

Steel bridges in Germany have traditionally been equipped with orthotropic decks. However, their number has strongly decreased against composite bridges with concrete decks. The reason for the increase in concrete decks is cost: 1m2 of roadway costs about € 800 for an orthotropic deck but only about € 300 for a concrete deck. In addition, an orthotropic deck is more sensitive to freezing which means its roadway can suddenly become slippery due to icing. A concrete deck is more robust and thus less sensitive to fatigue damage and is also stiffer than an orthotropic deck and thus the asphaltic wearing surface adheres better to it. German codes were changed in the 1980s, omitting limitations on tensile stresses in concrete roadway decks under service conditions. Instead, crack control has to be applied by a sufficient amount of finely distributed reinforcement so that the crack width is limited to 0.2mm. In this way the ineffective longitudinal post-tensioning is no longer necessary – ineffective because much of the compression force runs from the concrete deck into the steel trough due to shrinkage and creep. Today, only transverse post-tensioning is used. An exception to this rule is the latest development for bridge beams with corrugated webs. The cost for simple stiffened web steel plates have gone down in Germany during the last 20 years from about € 3000/t to about € 2000/t today, including erection and corrosion protection. Composite steel bridges are competitive for bridges with spans above about 60m because of lower costs and shorter construction periods. Corrugated webs can be less expensive than those with welded stiffeners if their production is automated. Even if a composite beam itself is more costly than an all-concrete one, the complete project may be more economic with a composite superstructure due to additional savings in shorter approach dams due to reduced beam depth, pier and foundation costs, shorter construction period and traffic interruptions. Taking into account life cycle costs the maintenance requirements of steel bridges in Germany are similar to those of concrete bridges with about 0.8% of construction costs per year, and smaller demolition costs for steel bridges than for concrete bridges. In Germany, the total length of all existing Federal bridges today comes to about 1600km, nearly 10% of which are all-steel or composite bridges. Their share is much higher for recent large bridges, e.g. for the new motorways in mountainous regions in East Germany. While in 1970 only 21% of all steel bridges were composite, their share has recently increased to 60% due to the above mentioned reasons. The German Public Roads Administration currently actively supports the following trends for major bridges: • for spans up to about 50m use incrementally launched concrete bridges, for longer spans use composite bridges, • for casting the concrete roadway slab use formtravellers which are supported from underneath in order to avo

Author(s): Svensson, Holger S

Keywords: composite bridges;steel;concrete;germany;case studies;construction work;design