The Need for Improving the Reliability of Reduction Factors and Deformations Used in the Practice of Seismic Analysis and Design of Structures

Abstract eng:
Based on the ductility of the structures, present wide world seismic code provisions allow to reduce elastic strength demands for a given structure system using constant reduction factors (R) and to reach maximum lateral non cyclic deformations limited to constant drift values for different types of structures. While both concepts are simple to use, this study demonstrates that they lead to unreliable designs. The main objective of this study is to find cyclic yield strength and deformation spectra of elastic perfectly plastic single degree of freedom (SDOF) structures subjected to several earthquake ground motions. The results of this investigation shows that: (1) R varies with the structure period (T), the characteristics of the strong motion, and the target cyclic (μc) or non cyclic (μnc) ductility ratio; (2) spectra based on μnc show sudden unexpected changes between two very close periods; (3) spectra obtained using μc are smoother than those based on μnc; and (4) the use of ductility ratios is not a reliable measure of damage due to nonlinear dynamic structural response. Damage arises not only due to the maximum lateral cyclic physical plastic deformation but it also results due to the enveloping physical ductility measured in the envelope of the complete hysteretic response, as well as due to the manner in which energy is dissipated. In addition, damage depends on the characteristics of the ground motion, not only on those of the severe expected earthquake but also on those of the subsequent aftershocks.

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