ABSTRACT
Within the scope of reassessement of older existing bridges in Germany, outdated stirrup types which are no longer permitted by current design standards (for example straight-legged stirrups) can often be found. As these stirrup types can nevertheless noticeably contribute to the shear capacity, the load bearing behavior of these bridge girders has to be further analyzed. In this context, 14 experimental tests on 0.8 m and 1.1m high, prestressed bridge girders with four different types of stirrups were carried out. In detail, beams with conventional closed stirrups, U-shaped stirrups with straight legs, insert-stirrups in the area of the intermediate support and two-part stirrups with a reduced overlap length were tested. To enable a continuous measurement of the strain along the stirrups, fibre optical sensors were used. As a result, the bond behaviour for each stirrup type could be investigated very detailed. The tests revealed that the overlap length of stirrups according to German standards can be significantly reduced and insert-stirrups in the area of the intermediate support, as well as U-shaped stirrups, do clearly contribute to the shear capacity. To enable testing of a high number of specimen with realistic cross-sectional dimensions and at reasonable effort, an innovative experimental setup was used for the tests. The basic concept of this setup, which is based on the substructure technique, is the application of the internal stress states using six individually controlled hydraulic jacks. This enables testing in real scale the behaviour of long girders on only short sections of the girders.
