Dynamic time-history analysis of reinforced concrete structures considering damage in the non-principal axis direction

A comprehensive study combining experimental tests and numerical analysis was conducted to investigate the damage mechanisms of reinforced concrete (RC) structures under seismic loads primarily acting in the non-principal axis direction. The results showed that joints subjected to non-principal axis loads experienced significant damage at the column ends, undermining the ‘strong column–weak beam’ design principle. Using the validated finite-element model, a RC frame model was developed and dynamic time-history analysis was conducted, providing insights into the damage characteristics of the structure, focusing on plastic strains, inter-storey drift and base shear forces. The findings showed that, when seismic loads act along the non-principal axis, the force mechanism of the structure changes substantially. In this direction, the structure exhibits higher load-bearing capacity and increased force demands, leading to significant plastic strains at the column ends and compromising the column hinge mechanism. These results highlight the need to consider the influence of orthogonal-plane beams on column-end restraints, as horizontal seismic forces in the non-principal axis direction may exceed those in the principal axis direction. Therefore, structural damage in the non-principal axis direction should be considered when evaluating and designing RC structures for seismic performance.