Influence of the ground motion directionality on the global ductility of 3D RC structures

This study examines the influence of ground motion directionality on global ductility μ_s of framed reinforced concrete structures. Suitable values of angle of attack θ, longitudinal reinforcement ratio ρ_l, dimensionless axial stress υ, and mechanical ratio of transverse reinforcement ω_wd were assumed. Detailed nonlinear modeling was adopted to reproduce the behavior of reinforced concrete elements in the plastic field, also considering the confinement effect on concrete mechanical properties. Nonlinear static simulations were carried out using the capabilities of the OpenSees code to evaluate the capacity curves and the corresponding global ductility. The results show that plastic hinges develop on the columns due to the combined effect of bending moments transmitted by the beams framing into the same joint for values of the angle θ equal to 30° and 45°. Consequently, the formation of soft-storey mechanisms significantly reduces the global ductility μ_s. A design formula is proposed to avoid such collapse mechanisms for framed reinforced concrete structures in ductility class high.