THIN-WALLED CONCRETE BRIDGES A NEW CONSTRUCTION METHOD FOR SUSTAINABLE BRIDGE STRUCTURES

Abstract

Recently two bridges across the rivers Lafnitz and Lahnbach were built in Austria, applying the balanced lowering method for the first time. In the balanced lowering method, the bridge girders are first assem-bled vertically and then rotated into the final horizontal position. The bridge girders and the compression struts were designed using thin-walled precast elements. After filling of the girders with in-situ concrete, the webs of the bridges were completed. On top of the webs, a deck slab was cast using a formwork carriage. While the filling of the thin precast girders with in-situ concrete permitted a fast construction of the webs, the production of the deck slab with a formwork carriage was a slow process. Therefore, a construction method for post-tensioned bridges with a plate girder cross-section was devel-oped, which would enable a fast production of the webs and the deck slab. In this new method, precast deck slab elements, which are stiffened by cross-beams, are placed on top of the webs. The precast U shaped girders and the deck slab elements can be installed along the whole length of the bridge with cranes or a launching gantry. The combination of precast U-shaped bridge girders and precast deck slab elements allows for a fast production of post-tensioned concrete bridges with a plate girder cross-section. In the span range from 30 m to 60 m, this method will make the erection of one span per week possible, thus achieving the same construction speed as segmental bridge construction. Compared with segmental box girder bridges, the new construction method permits a reduction of construction materials and avoids trans-verse joints in the completed structure. Therefore, sustainable bridges can be built with this new con-struction method, which will be described in detail in the paper.