Strength-reduction factors that are used to reduce linear elastic design spectra to account for the hysteretic energy dissipation of the structure are evaluated. The paper presents a summary of results of a statistical analysis of strength-reduction factors computed for single-degree-of-freedom systems undergoing different levels of inelastic deformation when subjected to a relatively large number of recorded earthquake ground motions. Special emphasis is given to the influence of soil conditions. Results indicate that for a given displacement ductility demand, the use of period-independent reduction factors is inadequate. Soil conditions can have an important effect on strength reduction factors, particularly in the case of soft-soil sites. It is recommended that strength-reduction factors to be used in design be specified as a function of the period and inelastic capacity of the structure, and of at least two types of soil conditions—one for rock and relatively firm sites and another for soft-soil sites. Following these recommendations, simplified expressions to compute strength-reduction factors are proposed.
[1]
Robert K. Green,et al.
Magnitude and Distance Scaling of Response Spectral Shapes for Rock Sites with Applications to North American Tectonic Environment
,
1989
.
[2]
Eduardo Miranda,et al.
Evaluation of site-dependent inelastic seismic design spectra
,
1993
.
[3]
W. J. Hall,et al.
Procedures and Criteria for Earthquake-Resistant Design
,
1975
.
[4]
Rafael Riddell,et al.
Response Modification Factors for Earthquake Resistant Design of Short Period Buildings
,
1989
.
[5]
Fawzi E. Elghadamsi,et al.
Inelastic earthquake spectra
,
1987
.