Algerian Seismic Code Research Articles

Evidence for fault-related directionality and localized site effects from strong motion recordings of the 2003 Boumerdes (Algeria) earthquake: Consequences on damage distribution and the Algerian seismic code

The Algiers–Boumerdes region has been struck by a destructive magnitude 6.8 ( M w) earthquake on May 21, 2003. The study presented in this paper is based on main shock strong motions from 13 stations of the Algerian accelerograph network. A maximum 0.58 g peak ground acceleration (PGA) has been recorded at 20 km from the epicenter, only about 150 m away from a PGA of 0.34 g, with both a central frequency around 5 Hz, explained by a strong very localized site effect, confirmed by receiver function technique results showing peaks at 5 Hz with amplitudes changing by a factor of 2. Soil amplifications are also evidenced at stations located in the quaternary Mitidja basin, explaining the higher PGA values recorded at these stations than at stations located on firm soil at similar distances from the epicenter. A fault-related directionality effect observed on the strong motion records and confirmed by the study of the seismic movement anisotropy, in agreement with the N65 fault plan direction, explains the SW–NE orientation of the main damage zone. In the near field, strong motions present a high-frequency content starting at 3 Hz with a central frequency around 8 Hz, while in the far field their central frequency is around 3 Hz, explaining the high level of damage in the 3- to 4-story buildings in the epicentral zone. The design spectra overestimate the recorded mean response spectra, and its high corner frequency is less than the recorded one, leading to a re-examination of the seismic design code that should definitively integrate site-related coefficient, to account for the up to now neglected site amplification, as well as a re-modeling of the actual design spectra. Finally, both the proposed Algerian attenuation law and the worldwide laws usually used in Algeria underestimate the recorded accelerations of the 6.8 ( M w) Boumerdes earthquake, clearly showing that it is not possible to extrapolate the proposed Algerian law to major earthquakes.

Estimation des périodes propres de bâtiments et vulnérabilité du bâti existant dans l'agglomération de Grenoble

ABSTRACT This paper presents a statistical study on fundamental frequency of vibration of a set of buildings situated in urban area of Grenoble (France). Correlations are established between the frequency and some building parameters (height, width, materials, type of structure). The formulas given by these correlations are compared with the ones of French Seismic Code PS92, Algerian Seismic Code RPA88 and American Seismic Code UBC88. A new formula for fundamental period for RC concrete shear walls buildings is proposed. This study has shown that fundamental frequencies of many buildings are situated in the amplification frequency range of the Grenoble site. Following this last result, a preliminary vulnerability study is started in order to estimate the seismic risk incurred by existing constructions.