Cracks are part of every reinforced concrete component and affect the durability and serviceability of those. The crack width may grow under long-time loading, which is mainly caused by bond creep. Current investigations at the Technische Universität Dresden focus on the bond behaviour and the bond stress distribution of ribbed steel bars under long-term loading. Different kinds of concrete are used, reaching from a mean uniaxial strength of fcm = 30 MPa up to fcm = 70 MPa. The experimental program includes systematic investigations of the influence of the bond length on the ultimate bond stress using pull-out tests and beam-end tests as well. In addition, tension tie tests under sustainable loading are conducted, the results of which will be used to validate calculated crack widths. The bond behaviour is detected by displacement transducers and fibre-optic sensors, which enable the quasi-continuous recording of strain. Based on the local resolution of the strain along an embedded steel bar, conclusions about the force transmission between reinforcement and concrete are made.
This article deals with the experimental and instrumental setup, results of the first test series and the procedure of evaluation. Furthermore, the results are compared to existing bond models and the influence of the test specimen and the bond length are discussed.