Zum Querkrafttragverhalten von Spannbetonträgern unter Ermüdungsbeanspruchung

摘要

The demands on the load-carrying capacity of bridges have increased over the last decades due to higher traffic volume. In the future, even a further increase of traffic loads is expected. Many existing bridge structures in Germany built in the 1960s and 1970s were designed for lower traffic loads applying the principal tensile strength criterion for shear. These structures typically feature a high degree of prestressing and low shear reinforcement ratios. In addition to the verification of the shear strength under static loading in the ultimate limit state, the shear fatigue resistance under service loads must be proved to account for the increased fatigue loads. In the past, the load-bearing behaviour of reinforced and prestressed concrete beams without shear reinforcement and with low shear reinforcement ratios under static shear loads has been investigated thoroughly and systematically. In contrast, the knowledge on the load-bearing behaviour under cyclic shear loads is very limited. Furthermore, the investigated parameters and material parameters of the available fatigue tests vary significantly impeding a direct comparison of the test results. Since the deterioration caused by cyclic loading and the resulting redistribution of forces within a member are not yet quantified, the existing approaches for shear fatigue do not yield safe and economic results at the same time. In case of prestressed concrete structures with a low amount of shear reinforcement it is not yet answered, if the provided shear reinforcement ensures a ductile failure behaviour. The aim of the presented work is a thorough analysis of the load-bearing behaviour of prestressed profiled concrete beams without shear reinforcement and with low shear reinforcement ratios under cyclic shear. At first, the state of knowledge on the fatigue behaviour of concrete and reinforcing steel as well as the shear strength of prestressed concrete beams under static and cyclic loading is summarized. Subsequently, own experimental investigations on prestressed beams without shear reinforcement (13 beams) and with low shear reinforcement ratios (14 beams) are presented. Numerical investigations of the tested beams under static and cyclic loading allow for an evaluation of the existing approaches of the static shear strength and a further analysis of the states of stress. Based on the experimental and numerical investigations models to determine the shear strength of prestressed concrete beams without shear reinforcement and with low shear reinforcement ratios under fatigue loading are developed. These models are then implemented in a modular verification procedure for shear fatigue of prestressed concrete bridges. Finally, the application of the developed verification procedure to a typical bridge structure is presented. The proposed procedure allows for a safer and more economical assessment of the shear strength under cyclic loading of existing bridges. It is incorporated in the revised edition of the "German structural assessment provisions for older road bridges" published by the German Ministry of Transport, Building and Urban Development.