consequences of the Recently Modification of Iran Seismic Design Code (No. 2800) (Due to A*B) and Proposing Forward Directivity Effect Coefficients (Na and Nv)

Document Type : Research Article


Iran University of Science and Technology, Tehran, Iran


This article intends to criticize and discuss the challenging of the design spectra in Iran seismic design (No. 2800, 4th version) mainly due to its two parametric form (A×B) and highlight its weaknesses regarding the current earthquake engineering principals. Examples of the discussed points include the predefined spectral shape as a fixed envelope of spectral ordinates at the constant maximum acceleration and velocity ranges, the dependency of corner period (Ts) to those of constant spectral acceleration, meaningless of the defined parameter (S) in spectral shape formula. The design spectral acceleration in the third and fourth 2800’s code are compared and assessed. A simple methodology for assessing the existing period dependent forward directivity effects parameter, N(T) is presented. The real spectral ordinates data at 120 near source sites from the two cities in the United State on four site soil types are used to develop the presented two parameters as representatives of FD-pulse effects; Na(T1) (for the constant maximum spectral ordinate range of period) and Nv(T) (for constant maximum velocity spectral ordinate range of period). The average values of the obtained design spectra are compared with those of the 2800’s third and fourth versions and the differences are the results are assessed. The resulted considerable differences confirm the necessary modification of the currently used design response spectra in the both period ranges of; the constant maximum acceleration spectra and acceleration spectra at the constant maximum velocity.


Main Subjects

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