Strength hierarchy provisions for transverse confinement systems of shell structural elements

Through-the-thickness (TT) confinement of masonry and concrete panels by composite or steel reinforcements, aiming at seismic retrofit of existing structures, has recently growth in popularity. However, structural design of transversal reinforcements, modeled as an homogeneized material, is often performed by neglecting the cyclic nature of seismic actions and by using static approaches. For this reason, a proper strength hierarchy between the confined core material and the confining devices should be accounted for in order to ensure that the retrofit system remains effective until the crisis of the core material is attained. This research introduces strength hierarchy conditions for TT-confinement systems, made of materials exhibiting a nonlinear behavior, aiming at determining the minimum strength required for uniaxial confining devices. The relevant relationships, theoretically derived by assuming a Drucker Prager constitutive model for the confined material and by enforcing equilibrium and compatibility conditions between the core and the confining devices, are characterized by simple mechanical parameters, usually available in common practice applications, familiar to most of the designers. Numerical examples confirm the effectiveness of the proposed provisions.