Structures must always be tested to meet the needs of a specific population. The Guadua cane is the most important genus of bamboo in America, endemic to this continent and consisting of about 30 species. Guadua angustifolia, native to Colombia, is the most important of these, thanks to its extraordinary physical-mechanical properties and the progress in its structural characterization that has been carried out in recent years. Although Guadua can be found in its natural state from Ecuador to Venezuela and between 0 and 2000 m above sea level, the optimal development of plants is reached between 500 and 1500 m, with temperatures ranging from 17°C to 26°C, rainfall of 700–1200 mm/year, and soils with moderate fertility and good drainage, characteristic of the central Andes region. For these reasons, many case studies have been reported by researchers in the aforementioned countries. In Asian countries such as India or China, there is also an important variety of bamboo for construction, reported extensively in the literature (Huang, 2021).

Figure 1 shows the natural growth of Guadua cane in the world and how it extends to both sides of Ecuador (National Geographic, 1980). This map is of importance because it gives an idea of where their constructions with this material are located and places where it is feasible to build them.

Figure 2 shows an example of a typical Bahareque house that can be found in the coastal region of Ecuador. This construction belongs to the city of Bahía de Caráquez located in the province of Manabí. As can be seen, the appearance of this type of building can even be very similar to that of traditional reinforced concrete houses due to social conventions.

This type of buildings can be found in countries such as Chile, Peru, Colombia and others in Latin America they often represent in historic constructions. This is the case of the study conducted by D’Ayala and Benzoni (2012), where they analyzed the response of historical structures to the earthquake that occurred in Chile in 2010. Although there were buildings that did not suffer major damage, they showed that it is essential to restrict the out-of-plane failure of such walls by adding buttresses or interior reinforcements in the walls (D’Ayala and Benzoni 2012). This failure is very common in this type of structure as opposed to traditional reinforced concrete structures. Another similar study carried out in Cusco, Peru (Brando, et al., 2019), also showed this behavior in the houses where 69% of the analyzed cases that did not take into consideration seismic aspects had presented it. The study also evidenced that the houses that did implement seismic design considerations including out-of-plane reinforcement were totally effective, so one of the recommendations given to rehabilitate the structures was to consider the out-of-plane reinforcement.

For thousands of years construction systems have taken advantage of similar concepts to bahareque structures. Apart of its popularity in Andean countries, other latitudes have also implemented some form of this system. Consider for example adobe in Spain, wattle-and-daub in the United Kingdom, cuje in Cuba and Caribbean countries, Quincha in Peru, pao-a-pique in Brazil, and Tabiquería in other parts of Latin America, just to name a few. Each country has its own traditions and methods for the construction of these type of houses (Kaminski, et al., 2016). The bahareque is a structure in the form of a skeleton, composed of wood and/or bamboo, with an open or split layer of cane of smaller diameter. In Spanish, the term used for the smaller diameter cut cane is “Esterilla.” A galvanized hexagonal wire mesh is used as a crack deterrent. The design is completed with an outer layer of mud, or mixture of manure, straw, and soil or even cement mortar. This latter layer must fill all the spaces of the structure and is placed after the assembly of the former elements (Gatóo, et al., 2014). The bahareque construction system uses the position of the walls (symmetrical, regular, and continuous) and their bolted joints, to form a single rigid system, as shown in Figure 3 (Taochuan, et al., 2020). According to several studies reported in literature, a properly designed bahareque house shall include:

• Floors: No more than two story are recommended. As the height increases, the overturning action of lateral loads increases. Since Bahareque structures are very flexible and lack a well-defined yield point, excessive deformations can occur at higher demands, which can lead to the collapse of the structure. Indeed, it is possible to increase the number of floors of a Bahareque structure, but this would require an additional structural analysis where specific material testing campaigns are conducted where the deformation capacity of the material is corroborated. This increases the use of materials, therefore elevating the final cost (Dixon, et al., 2015).

It has been shown that the shape of the bamboo is adequate to dissipate energy and therefore reduce the concentrations of damage. In addition to being a ductile material, the frame with diagonal elements allows the reduction of horizontal displacements during a seismic event. For example, in the study “Experimental and numerical studies on hysteretic behavior of all-steel bamboo-shaped energy dissipaters” used a bamboo-shaped cored steel with external metallic restraints, able to dissipate energy at high stresses with low adverse effects (Wang, et al., 2018). The failure modes of their model were generated by high lateral loads that resulted in bending deformations. On the other hand, (Xu, et al., 2019) showed that for masonry walls, the addition of Guadua elements such as chopped bamboo grids (which are used in Bahareque) improve their seismic performance. This fact is observed if the grid matrix is added externally, showing improvements in shear strength, deformability, and ability to dissipate energy. In addition, the study “Dynamic modeling and optimal design of Tube–Diaphragm coupling beam inspired by bamboo” showed that bamboo is the natural structure with the best absorption of specific energy and specified stiffness, thus the impact tests presented, confirm that bamboo is capable of modifying its natural frequencies by adjusting the number of diaphragms and the thickness of the section to accommodate disturbances in the environment by (Taochuan, et al., 2020).

A considerable limitation of bahareque system are pests. Like most wood materials, the canes used in bahareque are, prone to host insects. Nevertheless, this can be easily overcome by an adequate preventive treatment and continuous maintenance. The insects that commonly attack Guadua cane include bedbugs and termites (Parrella and Molari, 2021).

Homes of social interest can be purchased by families with limited resources, with full or partial government aid. These must have a minimum area of 50 m², and must comply with certain requirements, such as two bedrooms, one full bathroom, a living room, a kitchen, washing and drying areas, thus making it a decent and adequate home, focused on the low-income population (Pérez-Pérez, 2016). There are several price ranges for this type of housing, with costs ranging from US$ 13,000 to US$ 25,000. Low-income housing can be categorized according to its potential owners, if they are co-financed with government aid, or if they are completely financed by the government (Puri, et al., 2014).

Homes of social interest can be purchased by families with limited resources, with full or partial government aid (Puri, et al., 2014). These must have a minimum area of 50 m², and must comply with certain requirements, such as two bedrooms, one full bathroom, a living room, a kitchen, washing and drying areas, thus making it a decent and adequate home, focused on the low-income population (Pérez-Pérez, 2016). For populations that have the construction material available in their regions, the Bahareque houses are a more economical, ecological, and cultural identity alternative for the populations. By 2021, social interest housing in Ecuador follows a total cost range between $13,000 and $25,000. These houses are usually built with reinforced concrete, which is susceptible to increased costs due to transportation or price increases from mining operations. The cemented Bahareque homes for populations that have the material available in their region, costs can decrease between 35 and 37% (Ministry of Urban Development and Housing, 2020).

By using mortar for the walls, the resistance to fire increases considerably compared to the construction system that uses mud for the walls. However, details that compromise the wood framework (Guadua cane or others) must be taken care of, before electrical connections, stoves, and any stimulus for fire.

Bahareque, is a construction method that provides significant resistance to seismic events. Since Ecuador is located in an area of high seismic activity it is essential to ensure that these structures are safe from earthquakes. It should be noted that bamboo by itself is not efficient against lateral and compressive loads, and that its strength may be compromised by many other external factors such as: poor curation processes, variability in physical characteristics (diameter, length), variability in mechanical characteristics (aging, cracking, moisture), and unaware presence of insects (He, et al., 2014). In contrast, when bamboo is used as a component material of bahareque, embedded within cement or mud mortar, the earthquake-resisting capacity of the resulting composite panel increases dramatically. This was evident in seismic events such as the 2016 earthquake in Ecuador (M 7.8), where the seismic energy in some cases was mostly absorbed by the outer layers of the mortar, causing an exterior cracking also known as chipping. This damage to external portions of the wall could be easily repaired with a new coat of mortar and paint. Some damaged connections were corrected after inspection, (Moroz, et al., 2014).

An important characteristic of bahareque structures leading to a good seismic response is regularity in the walls, which shall rise in two directions perpendicular to the floor. Furthermore, it is not advisable to build walls on the strongest direction only and use another construction system on the weakest direction. The beam-column analysis of the Guadua elements does not provide an adequate view of the seismic resistance of this type of structure. Guadua elements must follow a regular pattern throughout the structure with height, thickness, design of the framework system and layers of homogeneous materials (Seixas, et al., 2017; 2021). On the other hand, the condition of symmetry in the walls must be followed: The proportion of the structural walls must be symmetrical in a bidirectional plane, both vertically and horizontally. In other words, a plan distribution as close to a square as possible is ideal, but rectangular models are allowed as long as their longer dimension does not exceed 1.5 times the dimension of the shorter side. If it is necessary to extend further the dimensions of one side with respect to the other, a separation of spaces must be made with simple joints, so that each space works independently and the desired proportion between walls is achieved (Xu, et al., 2019).

It is appropriate to add bracing elements or diagonals in the frames and floor diaphragms, this consideration provides stability against lateral loads, since it favors a more uniform dissipation of the seismic energy through the entire individual wall or through the floor diaphragm. In the case of the wall systems, the same Guadua cane is used for both the walls and the corner panels. For the individual walls, Guadua not only distributes the energy throughout the bamboo system, but also dissipates it on the outer walls (Wang, et al., 2018). Next, the floor diaphragms must be connected by bolted joints and ties, at their upper and lower walls to provide structural continuity in such a way that lateral loads are adequately transmitted. The wall system must be designed to support loads, both gravitational and lateral, and to achieve adequate load transmission, the connections must be bolted. To this end, a fish mouth cut, is used to connect perpendicular elements of Guadua. For diagonal connections 45° cuts can also be used. These connections are used to generate supports between elements and employ pre-drilled holes according to the bolt size, and then they are inserted between the Guadua connections and other wooden elements. For the connection of the foundation with vertical Guadua elements, anchor rods of sufficient length to reach the bottom of the foundation should be used.

It is important to consider water and humidity insulation. Water is one of the principal factors affecting the degradation of bahareque structures, so care must be taken such that it does not enter parts of the house. For the care of the roof, gutters distributed longitudinally in the fall of the roof slope are used, and then led to a collector through a PVC pipe. Waterproof paints are used along with overhangs to control moisture on the walls of the structure. Such overhangs must be designed at such a height that capillarity does not carry water from the floor to the walls. Although humidity and water are not direct causes of structural failure, they do represent serious damage to the wall system and reduce its mechanical properties (Archila, et al., 2018). Proper maintenance against insect pests must be established: this type of damage is extremely dangerous since it is not normally visible. In other cases, insects such as bed bugs or termites can eat a large part of the bamboo elements, causing the wall to collapse. It is important to check cracks and Guadua elements to certify that there is no insect damage and treat them if necessary (López-Muñoz, 2015). The quality of the Guadua cane should be according to the country’s standard with specifications that allow for the correct material to be identified by its condition, age, and color. However, these specifications are beyond the extent of the present study, and we suggest the interested reader to refer to NEC SE GUADUA (MIDUVI, 2016) for more information on this topic. Furthermore, the use of other types of wood in the construction of the wall system should follows similar guidelines.

To achieve a realistic and practical design, a two-story structure is presented and modeled herein. The distribution of spaces in the house was selected to take into account actual community demands, and to demonstrate that the proposed structural measures are feasible. Panels with vertical studs spaced 0.75 m from center to center are used. The extension of the longest side was defined to be 9 m, and the shortest side to be 6.30 m. These dimensions are in accordance with the principles of social housing, mentioned earlier. Perimeter walls and a central wall are used to generate greater stability. The walls are continuous since they are repeated both on the ground and high floor. The ground floor plan view is presented in Figure 5, whereas the upper floor plan view is shown in Figure 6. The wall systems, rigid diaphragm of both floors, can be seen as small circles between the wall lines in both figures.

The structure must contain framework panels with diagonals located at the ends of the wall. The walls must contain framework panels just as the concrete must contain a steel reinforcement, so that the Guadua cane (tensile strength), combines with the mortar (compressive strength), and forms a single material (cemented Bahareque) capable of resist loads of both types. In this way, the bahareque shear walls are capable of providing greater resistance to the structure, fulfilling the roof with the minimum length and weight requirements that satisfy the design parameters.

The structural design process of a bahareque structure follows a standard procedure. A detailed structural analysis procedure is presented in this section. As mentioned before, the panels of the structure should be as uniform as possible and the same for both floors and all walls. In this case, Guadua with average diameter of 10 mm is used in vertical stud elements such as columns, and horizontal studs elements such as beams and diagonals. The center-to-center separation is 0.75 m. The total horizontal length is 3 m, and the height of the panel is 2.5 m. The designed Guadua panel is shown in Figure 9.

The action of gravitational loads is caused principally by the weight of the walls with respect to other elements of the house. Therefore, the seismic design regulations must be followed. The results obtained with a test run in SAP2000 using gravitational loads are presented in Table 4.

The maximum values of internal forces produced by the gravitational load for the Guadua elements were thus obtained. With these values, compression, shear and bending stresses were also computed. For this model, the loads produced by the weight of the structure are of lesser importance and produce stresses within the range of allowable values. The admissible stress values can be reviewed in section 2.3.2. For the panels in both directions, the deformations produced by gravitational loads are as follows in Figure 14.

The action of gravity loads causes very small deformations in the slabs. A scaled-up visualization of the deformed shape shows that the deformations are greater in the center of the slabs with a deflection of 2.3 × 10^–4 m. This does not exceed the allowable deformation due to service loads for slabs stipulated by the IBC 2018 code in its table 1604.3 on Deflection Limits (ICC, INC, 2017), which for this building is 0.0125 m. Regarding the load supported by vertical studs, it should be noted that the admissible value of 16 kN was exceeded at the corners, where an action of almost 29 kN was observed. However, since, out of practical modelling considerations, the model employs one single frame per corner, and not the two-frame connection, this axial load is divided by two, producing a load of 14.5 kN, which falls within the ranges of the regulations.

The standard recommends a continuous reinforced concrete foundation, prior to a layer of cyclopean concrete. Then, for the upstand foundation, a confined masonry is recommended. A schematic detail of the foundation system is shown in Figure 21. Since it is a two-story structure, a raised concrete beam is placed under the upstand foundation, with a section of 0.40 m × 0.25 m and with bars and stirrups designed as if it were a reinforced concrete foundation beam. In this case, the loads are lower than those of a reinforced concrete house and do not require reinforcements with diameters greater than D = 12 mm.

The foundation has to support the load of the Guadua cane elements with the mortar walls and its other components. This load including the dead load and live load on the foundation is approximately 12.54 kPa, which represents a much lower value compared to the contribution of resistance of the foundation elements of 21 MPa. It is important to clarify that the dimensions and steel design results were specifically calculated for a two-story house. The importance of the foundation relies in providing a bahareque housing the stability that it cannot achieve by itself due to its lightweight. The base must be anchored in each right foot so that it can contribute to the transfer of loads and interaction between the bahareque wall and the reinforced concrete foundation.