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Behaviour characterization and rehabilitation of Earthen construction

2013-06-01

Earth has been used as a building material since ancient times until the present days due to its advantages such as simple construction methods or interior comfort.

Currently, one third of the world population lives in earthen houses, due to cultural, climatic and economic reasons. There is a vast architectural heritage stock which needs to be preserved. From the places and monuments classified as World Heritage, 10% are entirely or partially built in earth, and 16% of the ones that are in the list of heritage at risk are also built in earth. Until recently, earth has been a common construction material in Portugal. Adobe and rammed earth were used through years in almost all types of buildings. Adobe was concentrated in the littoral centre of the country, and rammed earth in the south. This utilization progressively declined since the middle of the 20th century, due to the development of the cement industry. At the present moment, Portugal still presents a vast number of earthen buildings, many of which are in use. There are numerous examples of buildings with cultural, historical and architectonic recognized value, namely of the “Art Nouveau” style, in Aveiro. In spite of this, there has been a general loss of traditional knowledge. On the other hand, little attention has been given to the study and conservation of this built heritage. As a consequence, many of the existing earthen buildings present various structural and non-structural anomalies and deficiencies. When under horizontal actions, such as earthquakes, earth constructions structures can suffer severe structural damage and sometimes total collapse. The seismic behaviour of earthen structures is typically characterized by fragile failures. Recent earthquakes that affected earthen buildings have evidenced their vulnerability, like in the El Salvador, in 2001, Bam, in 2003 and Peru, in 2007. Besides seismic events, earthen constructions are also particularly vulnerable to other agents, like water. But earth, as a building material, presents very attractive characteristics. It is low cost, locally available and recyclable. In addition, it possesses excellent thermal and acoustic properties, and is associated to quite simple construction methods that require small consumes of energy. These qualities are triggering an increasing interest among the community concerned with sustainable building. In spite of the increased interest, the existing knowledge concerning earthen construction is still mainly empirical. Few countries have codes for the rehabilitation and building with earth, and the existent codes are frequently incomplete. On the other hand, the study of earthen structures has been mainly oriented towards the architectural and historical aspects, while the material and structural characterization has been systematically relegated to a second plan. This lack of knowledge, together with a certain prejudice against earthen materials have been contributing to the disappearing of the earthen building stock, namely in many recent rehabilitation interventions has been practice to replace these materials. The fact that many times the earthen constructions have been built or repaired by staff without adequate training, contribute further more to this reality. In face of the described scenario, the project here proposed intends to study the behaviour analysis of adobe and rammed earth constructions along with the research of retrofit and performance enhancement solutions, considering the important patrimony existing in Portugal. The consolidation of this knowledge has a fundamental role on the preservation of the earthen heritage. In addition it will contribute to the development of earth construction as building solution following current structural demands. The methodology to accomplish the objectives includes: - The experimental characterization of the materials used in earthen structures, concerning their physical, chemical and mechanical properties; - The study of the structural behaviour of earthen constructions, especially when subjected to extreme horizontal loads, as those induced by earthquakes, with the conduction of experimental work; - The development of solutions for the repair, strengthening and retrofit of existing earthen constructions, validated with experimental work; - The development and calibration of adequate numerical models that allow the assessment of the structural fragilities and seismic vulnerability, with the proposal of adequate repair and strengthening solutions. A strong effort for the dissemination of the achieved results, among the scientific and technical community interested in earthen construction, will be made. The presented methodology will be implemented by a team of experts highly involved and active in the earthen construction thematic, who also possess solid experience and knowledge in related areas that will be of great use in the development of the project.

Reference: PTDC/ECM-EST/2396/2012

Date: 2013-2015

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