Issue 45

F. Brandão et alii, Frattura ed Integrità Strutturale, 45 (2018) 14-32; DOI: 10.3221/IGF-ESIS.45.02 15 I NTRODUCTION eritage constructions are a special group of structures with high artistic, cultural, religious, documental or aes- thetics value for the society. They represent, in some way, the cultural identity of a community preserving its his- tory over the time. Such constructions, playing an important role in the cultural heritage of many nations, are art works that contribute to the beauty of the built environment. In addition, attracting tourism, are an essential engine for the economic development of many cities and countries [1, 2, 3, 4]. As other types of buildings, heritage constructions are subjected to several scenarios of degradation and damage due to natural actions (thermal effects, chemical or physical attacks), anthropic actions and interventions (including alterations in the original building architecture) and also dynamic actions such as wind and earthquakes. For that, and considering its high cultural value, this special class of structures needs to be appropriately and periodically checked and maintained in order to assure structural safety conditions [5]. A large number of heritage constructions are located in seismic areas with different levels of seismic hazards, and there is a great interest from both the local administrations and the international organizations (UNESCO, ICOMOS, World Bank, etc.) to promote and support ad-hoc actions aimed to their preservation and maintenance. In this framework, based on the conservation of the World Heritage against earthquake loads, the scientific community plays a pivotal role, as also evidenced by the great number of researches published on this field in recent years [6, 7]. The study of the seismic behav- ior of masonry heritage constructions, shortly, is much debated than the one of new buildings because in case of historic constructions the occurrence of earthquakes, even if of small magnitude, may induce serious damages or even structural collapse. In general terms, the assessment of the seismic behavior of historic structures is very complex and depends on many factors such as the geometry of the structure, constructive typology, mechanical properties of materials, connections between the walls, etc. The mechanical propriety of masonry is one of the most challenging matters of the structural engineering because it is a heterogeneous, anisotropic and discontinues material due to the different types of components. For this reason, the reference values of the strength of the masonry material of the ancient constructions reported in liter- ature or codes are always conservative. As highlighted by [8], the assessment of the seismic behavior of historic masonry structures is a challenging task also because the structural skeleton of a historic building is usually capable of safely resist to gravitational loads, but poorly perform against horizontal loads (like the earthquake ones). According to [9] the study of the seismic vulnerability of historical constructions, that is, their susceptibility to damage un- der earthquake is very important because it allows to properly addressing the resources necessary to mitigate material and human losses. The seismic hazard is unavoidable; therefore actions aiming to minimize the impact of earthquakes on the structures should be directed to find solutions that improve the seismic performance of buildings. In the seismic analysis, and assessment, of historical constructions many numerical methods can be used [7], the most of them are based on discretization techniques that use the Finite Element Method (FEM). With respect to the analysis methods, it is possible to recognize three main categories: (i) the modal analysis, usually based on linear models and combined with the concept of structural behavior factor q to account for the energy dissipation effects that occur in the structure during the earthquake ground motion, (ii) the nonlinear static analysis (pushover methods) and (iii) the nonlinear dynamic analysis [10, 11, 12, 13]. The importance of a proper evaluation of the structural behavior of a heritage structure under seismic action - including proper method of analysis - is strictly connected with the historical and architectural value of these buildings and to the economic aspects of historic tourism in many countries [14, 15, 16]. Therefore is of high im- portance the need of analyzing the seismic response of a heritage structure in order to identify effective structural im- provement strategies oriented to both the protection and the conservation of the architectural heritage. In Brazil, the seismic hazard is considered low due to the country geographical position: Brazil is completely located on the South American Plate. However, recent history shows that earthquakes of high magnitudes have occurred in Brazil; for example: the Pacajús earthquake in the Ceará State, in 1980, of 5.2 m b magnitude [17]; the João Câmara earthquake in the Rio Grande do Norte State, in 1986, of 5.1 m b magnitude [18]; and also the most high earthquake ever registered in Brazil, the Porto dos Gauchos earthquake, in 1955, in the Mato Grosso State, of 6.2 m b magnitude [19]. In 2006 a technical norm of the Brazilian Association of Technical Standards (ABNT), “NBR 15421: Design of seismic resistant structures – Procedure” [20] was published and this norm currently classifies Brazil in 5 zones (from 0 to 4) ac- cording to their degree of seismicity. After the publication of this standard, the Brazilian research to evaluate the effects of earthquakes on structures has been growing, but in comparison to countries with high seismicity, such as Chile, Italy and Portugal, is still low. In the Brazilian scientific literature, still few are the case studies that analyze the potential effects of earthquakes on heritage constructions. This study aims to drive this growing field of research, discussing a representative case study in the city of Sobral. This city is located in the North region of Ceará State (Brazil), 230 km away from Fortale- H