In the past, shear design was based on a principal stress calculation in the uncracked state.
If the resulting tensile stresses stayed below a certain limit tensile stress, the required
transverse reinforcement could be chosen freely. This led to very low shear reinforcement
ratios, caused especially by the tough competition. In the case of an evaluation of the shear
strength according to the Austrian assessment regulations (Eurocode 2 und fib Model Code
2010) this structures are often unable to meet current standard requirements. Especially, in
the region near the intermediate support this lack of shear strength is particularly
pronounced, because due to the large bending moments and shear forces acts. According to
the state of the art this interaction of internal forces has a negative influence on the shear
resistance.
The shear behavior of post-tensioned continuous girders with a low amount of shear
reinforcement has been insufficiently investigated so far. Therefore, in the course of this
research project an extensive test series on large-scale post-tensioned continuous beams
with a low amount of transverse reinforcement will be performed. On the basis of
photogrammetric measurements a quantification of several shear-transfer mechanism acting
along the critical shear cracks will be carried out. Additional planned push off and shear tests
will investigate the shear carrying capacity according to aggregate interlock effect.
The own experimental data are subsequently extended by an exchange of experience and
test results with a BASt-project in Germany. As a result, a database with all shear tests will
be created. In addition, the experiments will be accompanied by numerical simulations in
order to get further information on influencing parameters, which will not be investigated
experimentally.
The main focus of this project lies on the further development of the shear model, which was
proposed by the TU Wien allowing the calculation of the shear strength of simply supported
post-tensioned girders with a low amount of stirrups. In this context it will be important to
clarify the question, if the described shear carrying mechanism (shear strength of the
compression zone, respectively the shear resistance due to the inclined compression chord)
of simply supported beams also occur for continuous girders. The proposed shear models for
the different regions specified by the occurrence of various types of cracks, will be modified
and further developed.
Based on stochastic analyses and on the dependence of remaining useful life the
deterministic calculation model will be transferred into a semi probabilistic design model.
Finally, in the course of a statical analyses of an existing post-tensioned continuous bridge
the potential of the further developed shear model will be pointed out.