SUMMARYAn investigation on the validity of the conventional design approach known as constant displacement ductility is carried out. The hysteretic behaviour described by the Modiÿed Takeda model is taken to represent the characteristics of reinforced concrete structural systems. The results presented in the form of seismic damage spectra indicate that the conventional design approach may not be valid because cumulative damage is excessively high. The inelastic design spectra based on the constant-damage concept are proposed in terms of simpliÿed expressions. The expressions are derived from constantdamage design spectra computed by non-linear response analysis for SDOF systems subjected to ground motions recorded on rock sites, alluvium deposits, and soft-soil sites. The proposed expressions, which are dependent on the local soil conditions, are functions of target seismic damage, displacement ductility ratio and period of vibration. The seismic damage of structures that have been designed based on this new design approach is also checked by a design-and-evaluation approach. The results are found to be satisfactory.
The validity of the conventional seismic design approach based on the well-known concept of "constant .ductility" is investigated. More than 130 earthquake ground motiori records are employed to represent seismic loadings of various characteristics. The design approach is considered valid if structures designed =cording to the approach can withstand these seismic loadings without sustaining excessive damage. The investigation is limited to SDOF structures with bi-linear behaviour, and the seismic damage is estimated using the Park-Ang damage model. The results in the form of damage spectra clearly indicate that the conventional design approach is not d i d for the c q of structures on soft soils because cumulative damage becomes excessively high. A new design approach based on a new type of inelastic response spectra called Constant-Damage Strength Demand Spectm is then proposed. The validity of the new approach is checked and found to be satisfactory.
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