Mechanical Non-Equivalence of Imposed-Strain Representations in Bond–Slip Modelling of Restrained RC Ties

Imposed deformations caused by shrinkage and temperature are a major source of early-age and serviceability cracking in restrained reinforced concrete (RC) members, including tanks, water-retaining structures and containment structures. A bond–slip-based finite-element framework is presented for simulating crack initiation, stepwise crack formation, crack-width evolution and reinforcement-stress histories in end-restrained RC ties. Three practically relevant representations of imposed deformation are compared: end-displacement-controlled axial deformation, prescribed shrinkage-type eigenstrain in concrete and thermal loading-inducing strains in concrete and reinforcement. The displacement-controlled model is validated against corresponding laboratory tests, whereas the shrinkage- and temperature-based representations are examined as comparative numerical scenarios under nominally equivalent imposed-strain levels. The results are interpreted in terms of evolving transfer lengths and tension stiffening. It is demonstrated through the analyses that matching a nominal imposed-strain level does not ensure mechanical equivalence between the three loading representations considered. Although the three approaches may produce comparable final crack widths in some of the analysed cases, they result in markedly different reinforcement-stress histories, transfer-length evolution and steel–concrete force redistribution. This distinction is important when the crack-width analysis is coupled with reinforcement-stress assessment or when imposed strains are superposed with mechanical loading.