THE FIRST TIMBER-CONCRETE COMPOSITE ROAD BRIDGE IN GERMANY

摘要

For the first time a timber-concrete composite (TCC) road bridge was built in Germany. For this purpose it was necessary to design a connector being suitable for bridge building. The so called stud connector with high values of slip modulus, ultimate load and sufficient stiffness was developed at the Bauhaus University Weimar. The Birkberg-Bridge near the small town Wippra has a span of more than 15 m. It is used as a single-lane road bridge across the river Wipper. The bridge is designed for traffic loads according to the national standard in Germany (DIN FB 101), which corresponds to the Eurocodes. The load consists of a 48 ton tandem system and a uniformly distributed load (UDL)of9 kN/m~2. The superstructure consists of a 25 cm thick concrete deck (C30/37) ductile connected with two timber main girders. The cross-section of one main girder has a constant height of 70 cm and a width of 1.26 m. The girders are made of glulam GL32h. The stud connector, which transfers the shear forces between concrete and timber, consists of a 3 cm thick steel plate with welded studs on the concrete side, whereby the bond to concrete follows the accepted principles of steel composite bridges. In contrast to this the bond to timber uses the principle of form-closure and functions as a traditional step joint. In this way the stud connector makes it possible to transfer the high loads of road bridges. This pilot bridge demonstrates the advantages of hybrid timber bridges compared to simple timber bridges. The concrete deck provides an ideal wood preservation. The distribution of high loads per axle and the transmission of horizontal loads could be realized much easier by the concrete deck. Furthermore construction details, proved in building of concrete bridges and accepted by the national highway administrations, can be transferred. In comparison to conventional concrete bridges the hybrid structure is lighter and more ecological. For the construction of hybrid timber bridges it is necessary to evaluate the long-term behaviour of the joint. Additionally, the paper presents the results of long-term shear tests with the stud connector over a period of more than four years. A proposal for the determination of the creep coefficient will be given.