Bond behaviour of structural concrete - Fibre optic measurements on single-reinforced tension ties

(original title: Verbundverhalten von Stahlbeton - Faseroptische Dehnungsmessung an einfach bewehrten Zuggliedern)

Author: Larissa Salis
Language: German

Abstract

Bond between reinforcement and concrete forms the basis of the structural behaviour of reinforced concrete. The crack width and crack distance are influenced by the properties of bond. Therefore, a precise understanding of the bond behaviour is of central importance for the description of the load carrying capacity of reinforced concrete and its dimensioning.

Previous research has led to the development of bond stress -slip relationships among several authors. Different influence factors are taken into account in different models, which is why they vary considerably. Until now, it was not possible to formulate a generally valid material law, which takes all influence factors into account. The use of new measuring technology intents verifying and expanding existing research on the basis of new test data.

Within the Master’s thesis of Larissa Salis, 11 tensile tests were performed on tension members with one reinforcing bar. These tension members were instrumented with a fibre-optic measuring system. The loading type, ( monotonous or cyclic loading) and the diameter of the reinforcing bar (14mm or 20mm) were the main parameters varied.
The fibre-optic measuring system enables a quasi-continuous measurement of strains along the reinforcing bar inside a specimen, without substantially disturbing bond between reinforcement and concrete. Steel stresses, bond stresses and slip were calculated from the measured strain. From this data, the bond stress-slip relationship of individual points was experimentally determined.
The conducted experiments with fibre-optic strain measurement provide new data for further investigations of the bond behaviour of reinforced concrete. However, the evaluation of this data is relatively complex. The quality of the strain measurement was improved compared to previous applications.

Assumptions of existing models, which are mainly based on pull-out tests, were checked regarding their validity for the conducted experiments. A comparison of the experimental data with the model of Eligehausen et al. showed large deviations. The analysed data did not show any correlation between the shape of the bond stress-slip relationship and the type of loading.