Discontinuous yielding in bare and embedded reinforcing bars: Implications on the determination of steel and bond shear stresses from strain measurements

Distinct jumps from the yield strain to at onset of hardening occur in bare reinforcing bar exhibiting a plateau once limit is reached. These discountinuities known as Lüders bands nucleate single locations and travel along axis constant load. In contrast, no such were observed recent experiments with bars embedded concrete instrumented using distributed fibre optical sensing (DFOS). Instead, increased gradually where was exceeded. This observation, made possible by high resolution DFOS, cannot be explained entirely effect tension stiffening. While bond stresses cause variation steel and, hence, indeed prevent propagating bars, distinct would still expected stress The different stress–strain behaviour rather attributed three-dimensional state induced locally concentrated forces ribs. presumably (i) direction maximum shear vary over cross-section, leading loss macroscopic phenomena, (ii) reduce nominal axial tension. As consequence altered behaviour, simple conversion strains stress-strain relationship derived uniaxial tensile tests leads incorrect results for range slightly below up hardening. findings are most relevant experimental studies investigating since researchers rely on validity material law derive validate stress-slip relationships. paper presents mentioned experiments, discusses differences between potential explanations, outlines implications determination based measurements concrete.