Decoupling Criteria for Inelastic Irregular Primary/Secondary Structural Systems Subject to Seismic Excitation

The present work deals with the dynamic response of structures that are irregular in height, consisting of two parts, a lower part made of concrete and an upper part made of steel. Irregularity is due to different dynamic responses of the two parts, here expressed by their different damping ratios and inelastic material laws. The seismic design of such structures is not satisfactorily covered by current design codes, especially if a decoupled procedure is chosen for the analysis, where the lower part is excited first and its response is used as excitation for the upper part. The present paper aims at contributing toward better understanding of the interaction between the two parts and at proposing improved decoupling criteria for the seismic analysis of inelastic primary-secondary systems. Toward that goal, each part is modeled as a one-degree-of-freedom system, and the maximum responses of coupled and decoupled inelastic time history analyses are compared over a wide range of dynamic characteristics and strength levels of the two parts. The results are presented in the form of error levels between the two alternative analysis procedures. © 2010 ASCE.