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) the 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 behaviour 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 statistical analyses of an existing post-tensioned continuous bridge the potential of the further developed shear model will be pointed out.