Les Caractéristiques structurelles des maisons de la Casbah d'Alger ( Tests et simulations)

Abstract

The organization of traditional urban fabrics into aggregates is one of the main characteristics of vernacular architectures such as the Kasbah of Algiers. The latter underwent an almost total reconstruction after the 1716 earthquake. Beyond the macrostructure configuration of the houses, various empirical and preventive techniques were used to reduce the seismic vulnerability of the houses, the effectiveness of which scientifically remains undemonstrated. Through multidisciplinary research, we study the structural characteristics of the houses of the Kasbah of Algiers connected in the form of a compact aggregate category. We first proceed with a mechanical characterization of historic building materials followed by a series of static and seismic finite element structural analyzes at different scales. A historiographical, methodological and operational contribution is proposed in order to restore the image of the historic center and ensure its sustainability. For this, we propose a complete and multidisciplinary methodological process of a structural rehabilitation project of an authentic aggregate from in-situ 3D scanning to the proposal for structural intervention. First, an urban analysis highlights three distinct categories of aggregate allowing the selection of a representative case study. The latter is the subject of a series of technical surveys including the application of 3D lasergrammetry allowing 188 scans to be obtained. The generated point cloud is an essential reference during the 3D modeling process based on the ten Grades of Generation and on a series of software based on BIM and NURBS. In addition, mechanical characterization through destructive, semi-destructive and non-destructive tests is carried out on samples of historical terracotta bricks, lime and clay mortar and Thuja logs. This step reveals values higher than those suggested in the literature and enriches the database of the properties of building materials for houses in the Kasbah of Algiers. Parameterized Finite Element Modeling FEM is therefore carried out thanks to the HBIM model obtained with a high degree of accuracy as well as the mechanical characteristics of building materials. Different analyzes are undertaken including Static Linear Analysis LSA, Modal Analysis MA and Pushover Analysis PA considering different configurations of the aggregate: with and without rigid horizontal diaphragms; in the aggregate and disaggregated state. The results clearly demonstrate a better structural response of the aggregate at the aggregated state rather than the disaggregated one highlighting several local collapse mechanisms. These are the subject of a targeted structural upgrade proposal in order to improve the structural performance of this category of aggregate and consequently reduce its seismic vulnerability. Three distinct strategies are proposed in accordance with the recommendations of international restoration charters as well as those resulting from the various structural numerical simulations. The tie rod system is chosen as the most advantageous technique and is the subject of another post-intervention seismic structural analysis. The latter demonstrates a considerable reduction in the seismic vulnerability of the aggregate in all directions. The structural rehabilitation project constituting a complete guide for vernacular architectures, is completed by a reference catalog of the local collapse mechanisms of compact type aggregates.