Influence Of Structural Damping On Seismic Strength Reduction Factor

The seismic strength reduction factors are not only the basis to determine theinelastic response spectra for performance-based seismic design, but also the keyfactor to determine design seismic force for force-based seismic design. This workinvestigates the influence of structural damping on strength reduction factor,including the effects of the effective ground motion duration and modal dampingnumber on ductility reduction factor. The main research contents and conclusions areas follows：(1) The research background and progress are illustrated. The research onstrength reduction factor is abundant in foreign areas and seldom in the domestic.Presently there are many studies on inelastic response spectrum for shear-typestructures, but few for the bend-type structures.(2) Employing the displacement response spectra of single-degree-of freedomsystems with different damping ratios, the present study investigates the effects of theeffective ground motion duration, from25Chi-chi earthquake records and harmonicsine wave, on damping reduction factor. The study shows that damping reductionfactors decrease with increasing the effective duration of the ground motion and thenumber of cycles of harmonic excitation. A nonlinear multiple regression analysisbased on the statistical mean value is employed, and a modified damping reductionfactors considering the effects of ground motion duration is suggested.(3) The effects of higher modal damping on ductility reduction factor for theframe-shear wall buildings are studied. Based on the planar structure and using5ground motions, the elastoplastic dynamic analysis and static elastoplastic pushoverare performed to investigate the coupling effects of the modal damping number,stiffness characteristic value and vertical irregularity of structure on ductilityreduction factor on the basis of the global displacement ductility. The resultsdemonstrate that modal damping number has important effects on ductility reductionfactor. Ductility reduction factor decreases with the increasing the modal dampingnumber and it is almost invariant as to consider more modal damping number. Modaldamping number and stiffness characteristic value have important interaction effectson ductility reduction factor, while modal damping number and vertical irregularityhave indistinctive interaction effects.