BALANCED LIFT AND BALANCED LOWERING METHODS FOR COST AND MATERIAL EFFICIENT CONCRETE BRIDGES

Abstract

The new bridge construction methods consist of building the bridge girders in a vertical position and of rotating the bridge girders into the final horizontal position. In order to rotate the bridge girders, additional compression struts are required. In some topographical situations it will be more efficient to produce the bridge girders with these innovative methods than with the traditional incremental launching method or the balanced cantilever method. The span of the bridge girders is reduced by the compression struts which enables considerable savings in construction materials. Bridges with inclined compressions struts have been built in the past in order to reduce the bending moments in the bridge girders and hence to reduce the material consumption. But in these bridges the compression struts were either added after the construction of the bridge girders (e.g. Haseltal Bridge [1]) or were built with a laborious cantilever construction method (e.g. Bridge across Zahme Gera [2]). In the balanced lift and balanced lowering methods the compression struts are already essential structural elements during the construction process and serve to reduce the bending moments in the bridge girders in the completed bridge. Recently the balanced lowering method was used to build two bridges across the Lafnitz and Lahnbach in Austria. As a result of the bidding process, it could be shown that the superstructures of the post-tensioned concrete bridges did cost 25 % less than the originally planned steel-concrete-composite bridges. The construction of the steel-concrete-composite bridges would have required a construction height of 4.6 m. Using the balanced lowering method, the height of the deck of the post-tensioned concrete bridges could be reduced to 2.0 m. This proves that considerable amounts of building materials can be saved by applying the balanced lift and balanced lowering methods, which will contribute to the construction of sustainable bridges.