Seismic Response of Inelastic Structures Subjected to Bidirectional Excitations

Abstract

<p>A study has been made of the inelastic seismic response of single story structures having symmetrical as well as symmetrical configurations and subjected to bidirectional excitations. The intent of this investigation was (i) to assess the significance of force interaction in yielding of columns in the analysis of inelastic structures, (ii) to privude guidelines as how to account for the bidirectionality of the ground motion, and (iii) to clarify the role of "eccentricity" in the lateral-torsional response of inelastic asymmetrical systems.</p> <p>The elasto-plastic responses of symmetrical systems, with interactions effects included or ignored are presented for sinusoidal base motions as well as earthquake ground motions. The latter excitation consisted of five pairs of recorded earthquake ground motions. It is found that the interaction effect is significant for stiff structures with low yield strength and it increases the response. The increase becomes substantial for very stiff structures. For this type of structure, an elasto-plastic analysis using uniaxial excitation could seriously underestimate the displacement ductility demand. It is recommended herein that such structures to be designed remain elastic or almost elastic under expected earthquake disturbances. Taking the interaction effect and the critical orientation of ground motion components into account, the ductility demand can be up to 40% larger than the estimates calculated otherwise.</p> <p>An inelastic analysis of single mass monosymmetrical structural models subjected to the two horizontal components of ground motion is performed. A new concept of eccentricity based on the yield properties of the resisting elements is proposed as a better index to denote the severity of torsion on the inelastic response of asymmetric systems. The ductility demand of asymmetric structures with uniform strength distribution, i.e. with zero plastic eccentricity, are found to be not much different from those of symmetric structures.</p>