Inelastic Structural Response to 2D Ground Motion

According to current seismic design philosophy, structures are allowed, for economic reasons, to undergo deformations well into the inelastic range when subjected to a strong motion earthquake. Results presented show that the simultaneous action of both horizontal components of ground motion produces significantly larger displacements than those produced by a single component for stiff structures proportioned according to the Uniform Building Code. The magnification of response due to biaxial motion depends primarily on the initial fundamental elastic period of the structure and on the amount of inelastic deformation which a single component of ground motion would produce. The interaction of gravity loads with these increased displacements can cause the P-Δ effect to be more critical than for one-dimensional ground motion. The numerical results presented are for a series of single and three-story structures with elastoplastic uniaxial restoring force characteristics.