The anti-seismic capacity and enhancement of earthen structures. Earthen architecture for the urban context of Bogotá, Colombia

The passive and vernacular technologies in architecture are known for their excellent thermal behaviour, low environmental impact and their cultural value. Mostly, the contemporary projects that have been developed using vernacular technologies are referred to rural environments, solving important problematics as scarcity of resources, lack of facilities or low-income dwellings. However, if one of the goals of architecture for the sustainability is to contribute in a good way to the climate change, why not to focus these efforts also on big cities where are produced the most robust impacts? Hence, the starting point of the present research is to identify the possibilities of enhancing earthen material to increase its feasibility as architectural technology for urban projects. Considering (i)the historical influence of the modern movement, the industrialization and the globalization on developing countries; (ii)the lack of investigations on earthen technology for architecture; (iii)the nature of traditional earthen architecture as a vernacular technology ; (iv)and the nature of a big urban context that is heterogeneous and full of industrialised materials, the first proposal of the present document about the feasibility of an earthen project in a high density city may seem to be incoherent. Nevertheless, the point in common of all those aspects is the actual scenario of climate change, the influence of the cities in sustainability affairs, and the advantages that earthen construction technology can offer for more sustainable architecture. In that way, there appear punctual aspects that have to be solved to enable the real use of earthen construction in a city. Which are the limitations of the raw earth technologies and how can they be overcome to include those projects in a city context? There are already regulations that standardize the use of this technology? Which are the weak points of an earthen building and how can be enhanced? To solve these and further questions, this work is limited to a physical context, hence there can be evaluated real aspects that are not allowing the raw earth techniques to be widely used in urban fabrics. Is chosen the city of Bogotá, capital of Colombia, as an urban scenario to hypothesize the use of earthen technology. Is a typical Latin American capital that offers a dramatical complexity considering social, political, economic and cultural aspects. As a city of a developing country, Bogotá has big inequalities that are evident in the city architecture. Millions of people live in self-construct houses that probably are not following constructive regulations. Consequently is notable the extended use of earthen technologies in developing countries as economic solutions that present dignity conditions for the inhabitants. On the other hand, Colombia has a huge heritage of traditional earthen technologies (Tapia -rammed earth-; Adobe -raw earth bricks-; Bahareque -wood & raw earth-) that, as in different parts of the world, had lost importance and were near to disappear because of the industrial revolution and the modernist movement. Treasuring those techniques and considering a contemporary one (CEB -compressed earth blocks-), the present research is focused on them. To create a complete understanding of these techniques, here is made a description of their designing and construction process. From that is expected to identify weakness and thus propose solutions that can be implemented to increase their availability to be used in Bogotá. To focus even more the investigation, there are identified limitations that earthen buildings have when are proposed into urban contexts, thus the present research can be focused on one of them. First, considering that Bogota is located in the high seismic region of the Andes, is necessary the use of anti-seismic strategies into the building construction, these can be based on several investigations or regulations. A second obstruction is the restriction of finding the material, as all the surroundings in a city plot are already constructed and the transportation of soil can increase costs and energy consumed. This limit the use of the raw earth to peripheral areas where can be easier to find nearest material sources. In addition is evident the ignorance about this technology. Is possible to say that generally architects, engineers, workers, or even the inhabitants have not enough information about earthen buildings and these are widely related to poor constructions that are not “safe” or well seen. Finally, as earth is not a spread material for construction there is a lack of products and solutions offered from the constructive industry (tools, materials or technical solutions to be used in a construction site). In light of above, it was early understood the need for an analysis of the seismic-resistant behaviour of the raw earth constructions. Earthen buildings are vulnerable to seismic loads due to three main aspects: the performance of the entire building in relation to the type of structural system which is limited by the lack of tensile and bending strength of the material. The anti-seismic reinforcements for earthen architecture that are found in literature are organized on three strategies that regard the vulnerabilities of earthen buildings under earthquakes: the understanding of the building as a whole by a building behaviour strategy, a structural strategy to guarantee the box-behaviour, and a load-bearing wall strategy referred to the strength’s enhancement of the main structural elements. Under these three main strategies the present research is presented as a compilation and a guide of appropriate construction methods for earthen buildings on the seismic hazard zones of Colombia, with a large focus on the anti-seismic strategies and reinforcement. Unfortunately, in Colombia there is a lack of regulations for raw earth buildings even on what concern to seismic safety (on new or heritage buildings). The current anti-seismic regulation “Reglamento Colombiano de Construcción Sismo Resistente 2010” (NSR-10) does not present any chapter related to earthen techniques. However, in several Latin American countries there have been developed studies, investigations and even laws that create a framework about the raw earth seismic capacities and the solutions that can be applied to improve the building respond to an earthquake. These are considered as solutions that can be applied in Colombia to construct seismic resistant earthen buildings. Nevertheless, this work is not the first approach to anti-seismic earth constructions in Colombia. There is a group of architects and engineers that are proposing a new regulation to include earthen buildings in the seismic-resistant construction regulation (NSR-10). The present research is also based on the work of those colleagues, and it is expected this document can be presented as support to the regulation that they are developing. This situation frames the current work into a contemporary and real scenario of our profession. From the investigation related to load-bearing wall strategy, are identified the “enclosing reinforcements” as an effective opportunity for raw earth buildings. With this identification, the research studied the possibilities to improve earthen plasters that – as the mentioned reinforcements – naturally enclose all the wall elements. In cooperation with Luciana Restuccia from the department of structural, building and geotechnical engineering (DISEG) of Polytechnic of Turin, is considered the use of biochar particles that can be added to the plaster mixture. The investigations carried by Restuccia confirm an enhancement of the mechanical strengths in cementitious composites. In that sense, as starting point for further researches there is proposed an earthen plaster enriched with biochar additive (EPEB) pretending to find an improvement on the mechanical strengths of the plaster and the entire earthen wall under seismic conditions.In consideration of the sustainable advantages of earthen construction, there is questioned the feasibility of an earthen building in the urban context of Bogotá, Colombia. Several aspects of earthen buildings and Bogotá’s context are analysed: the construction process of earthen buildings, the constructive regulations and earthen traditions in the country, and the geographical and socio-economic conditions in Bogotá. Hence is made a research on the main earthen techniques of the country: tapia (rammed earth), adobe, bahareque and CEB, their characteristics and construction processes are shortly described in order to find why these are not largely used in cities. In coherence to the seismic hazard of Colombia the investigation has special focus on the structural and anti-seismic capacity of earthen architecture, as an aspect that requires enhancement to enable earthen buildings to be constructed in Bogotá. Thus the present document is proposed as a manual of anti-seismic solutions for earthen buildings. There are identified three main strategies to enhance the earthen buildings in seismic zones: the entire building behaviour; the box-behaviour of the structure; and the enhancing of load-bearing wall strengths. Furthermore than the appropriate constructive procedures, this investigation was deepened in the enclosing reinforcements for earthen load-bearing walls. Based on structural reinforcements for generic plasters and the mechanical enhancement of cementitious composites with micro inert biochar additive, here is proposed as technological innovation the experimental investigation to test an earthen plaster enriched with biochar additive (EPEB) expecting it can contribute to enhance the structural stability during earthquakes