Impact on the Dynamic Characteristics of Reinforced Concrete Buildings in Algiers Following Two Seismic Events Yamina Ait-Meziane, Rania Souici, Nabila Guessoum, Djilali Bouziane, and Khadidja Abbes Abstract Most of the housing stock of the old cities in the north of Algeria is on masonry and reinforced concrete. These agglomerations are located in the coastal strip, which are precisely exposed to a high seismic hazard. As a reminder, the north of Algeria has been shaken by several major and moderate seismic events. In the case of Algiers, for the greatest part of the area the buildings were constructed during the 1871–1936 period, so bearing the traces of several earthquakes since no major reinforce- ment campaign was undertaken. This paper reported the analysis results of the impact of a seismic event by considering the fundamental period of the reinforced concrete buildings identified before and after the earth- quake. A comparison between the obtained results with the site conditions were operated using a non-destructive technique, that of background noise. Keywords Building Á Soil Á Frequency Á Earthquake Impact 1 Introduction The urban centers of northern Algeria consists of masonry buildings and have been densified by reinforced concrete buildings during the 1920s. The first reinforced concrete buildings built in Algiers were inserted into the existing urban fabric for some and, into the periphery for others. The example of the district of Bab El Oued illustrates this state. In Fig. 1, the cities Consolation and Press were inserted inside the ancient urban fabric and the cities Taine and Eucalyptus on the outside. To absorb the demand for housing, these buildings were built on several levels, iso- lated block for some and several blocks separated by seals for others. Their design was achieved, like masonry build- ings, to support vertical loads. Seismic activity in the Mediterranean basin is concen- trated in northern Africa, where oblique convergence between the African and European plates is accommodated and Algeria is one of the most seismic countries [1]. Old agglomerations are located along the coast, an area exposed to high seismic hazard. Mw = 6.8 [2, 3]. On August 1st, 2014 a moderate earthquake (Mw = 5.5) hit the Capital city of Algiers and its surroundings. Thus, most of the old housing stock experienced many major earthquakes [4]. Algiers is classified in zone III (high seismicity) according to the Algerian code (RPA 99/2003) [5]. The post seismic expertise carried out after the 21st May 2003 earthquake on reinforced concrete buildings located in Algiers concluded to a green classification. This category corresponds on the macroseismic scale to a pathology that does not require repair or reinforcement of buildings. This level of diagnosis allows the immediate reoccupation of buildings. The scope of this research is to present our contribution to improve the post seismic diagnostics of buildings to account for the dynamic structural parameters before and after a seismic event. The diagnosis has become quantitative and not qualitative. The experimental frequencies obtained from buildings supplemented by the knowledge of the ground frequency must give us information on the probability of ground-structure resonance which aggravates the seismic behavior of buildings. Prevention to reduce the risk of damage would consist in proposing a solution to keep the frequency of the buildings from the ground frequency as far as possible. Y. Ait-Meziane Á N. Guessoum Á D. Bouziane Á K. Abbes National Earthquake Engineering Research Center, CGS, Algiers, Algeria R. Souici (&) FGC, LBE, University of Science & Technology Houari Boumediene (USTHB), Algiers, Algeria e-mail: souicirania@gmail.com © Springer Nature Switzerland AG 2019 N. Sundararajan et al. (eds.), On Significant Applications of Geophysical Methods, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-030-01656-2_44 195