Multiscale non-linear analysis of RC hollow piers wrapped with CFRP under shear-type load

A multiscale approach is proposed for shear and flexural modeling of unstrengthened and FRP-wrapped hollow members. Proposed confinement model (at material level) and computation algorithm (at section and member level) are able to predict the fundamentals of the behavior of hollow confined members in terms of strength, flexural behavior and ductility. The confinement model explicitly accounts for different radial and circumferential confining stresses in hollow sections and is able to trace the evolution of stresses and strains in concrete and confinement jacket allowing to evaluate at each load step the multiaxial state of stress and FRP failure. The computation algorithm traces the occurrence of brittle mechanisms, namely concrete cover spalling and reinforcement buckling (typical failure modes of hollow members) and accounts for main sources of member deformability. Only in few cases hollow members, usually adopted as tall piers, suffer shear failures. Results of theoretical analyses and experimental tests, available in literature, show that good agreement was achieved.