Shear Capacity of Concrete Members under Monotonic and Cyclic Loading

Abstract

To date, a reliable assessment of shear safety of concrete members is a challenging task for evaluation of existing concrete structures such as bridges. Available investigations and models for determination of shear capacity are often based on diagonally cracked members and assure the shear safety mainly based on provided shear rein-forcement. Application of such models results often in a calculated lack of shear resistance due to deficient shear reinforcement, although existing concrete members are often free from diagonal cracks. To avoid over-conservative evaluations in such cases, the shear capacity provided by concrete tensile strength would be evaluated in this thesis. A safe consideration of this load-bearing mechanism for members subjected to cyclic service loads e. g. traffic loads requires, however, an adequate consideration of cyclic damage on concrete tensile behaviour. At first, concrete tensile behaviour under uniaxial tension is investigated using conducted tensile tests on cyclically damaged members and a compiled database of cyclic tensile tests. The findings are used to propose a tensile curve for cyclically damaged concrete. In the second part, cracking of concrete members under shear loading is evaluated using provided mechanical models and shear tests in the technical literature. A database of monotonic and cyclic shear tests on reinforced and prestressed concrete members without shear reinforcement with provided data on diagonal cracking is compiled. Based on monotonic tests of the database, a mechanical model is proposed for a better approximation of diagonal cracking load. This model is adapted later on to derive mechanical models, which account for prestressing as well as cyclic damage. In a higher approximation level, some benchmark shear tests are evaluated using nonlinear finite element (FE) analysis to propose a refined model configuration for reliable assessment of diagonal cracking of shear critical members. The refined model configuration is validated in a further step using the monotonic tests in the shear database. In addition, recommendations are made for numerical prediction of the diagonal cracking load of cyclically damaged concrete members. Finally, the results of the theoretical, experimental and numerical investigations are summarized in proposals for determination of the shear capacity of members under monotonic and cyclic shear loads at the state of diagonal cracking using mechanical and numerical models.