Experimental investigation of bond and crack behaviour of reinforced concrete ties using distributed fibre optical sensing and digital image correlation

Abstract

The interaction of reinforcing steel and concrete is decisive for the structural behaviour of reinforced concrete (RC) in the serviceability and ultimate limit state. In the past decade, distributed fibre optical sensing (DFOS) and digital image correlation (DIC) have emerged as valuable tools to investigate and comprehend the mechanics of this interaction in more detail. This paper presents and discusses the results of an experimental campaign comprising 21 RC ties subjected to monotonic and cyclic uniaxial tension, where these refined instrumentation methods were utilised to study the influence of the reinforcing bar diameter, rib geometry and mechanical properties on the structural behaviour. Local strains were measured along the reinforcing bars with DFOS, from which the distributions of steel and bond stresses, as well as slip were derived. The crack pattern and kinematics on the surface were determined through DIC. The results allowed studying the influence of the deformation level, cyclic loading and the rib geometry on splitting and the magnitude of local and average bond stresses. The results indicate that the bond and crack behaviour depend on parameters typically neglected in design standards, such as the relative rib area, elastic steel stiffness, and bar diameter. Moreover, the observed average bond stresses in the elastic range were lower than proposed by design standards for serviceability verifications. These observations allow identifying weaknesses and inconsistencies in common bond models, serving as a starting point for improvements in modelling.