Narrow Results

This paper summarises the results of comprehensive statistical study of response and design spectra in which a total of 106 Iran's horizontal acceleration components recorded during various earthquakes was considered. Special emphasis is given to the influence of effective duration of strong motion, soil condition and damping ratio of structure on elastic response and design spectra. The study included both deterministic and probabilistic approaches. The records with peak ground accelerations greater than 0.05 g from 23 stations in 47 seismic events are divided into four soil categories in accordance with Iranian seismic code. For each soil group, mean and mean plus one standard deviation spectral ordinates were computed for: effective duration of strong motion and damping ratio of structures and also a design spectra for different soil conditions has been constructed by deterministic and probabilistic approaches and results have been compared with code provisions (i.e. NEHRP, UBC, EC8 and seismic code of Iran). The influence of effective duration of strong motion has been studied by definition based on energy of accelerogram. The paper also presents an evaluation of the damping ratios on the response spectra. Results and conclusions from this study can be directly used for the evaluation of the present Iranian seismic code in order to construct new design spectra and also for the evaluation of seismic design provisions.

The validity of the conventional seismic design approach based on the well-known concept of "constant ductility" is investigated. More than 130 earthquake ground motion records are employed to represent seismic loadings of various characteristics. The design approach is considered valid if structures designed according 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 valid for the case 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 Spectra is then proposed. The validity of the new approach is checked and found to be satisfactory.