Category: North & Central America

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Report #164: Reinforced concrete frame with lightly reinforced masonry infill

by Laura Redmond, Reginald DesRoches

This type of home is a reinforced concrete frame building with brick infill on the second story. The infill may be lightly reinforced and the first story is either left open to prevent flooding in hurricanes, or later, when the individual has more money the bottom story is often infilled with masonry (which is not tied into the frame). This construction practice may make these structures vulnerable to seismic events as the building is effectively a large mass placed on top of a very flexible soft story. Additional vulnerabilities may stem from settlement of the wood pile foundations as the soil conditions are variable and generally no formal geotechnical surveys are done in Belize.

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Report #165: Timber Stilt Homes

by Laura Redmond, Reginald DesRoches

This construction type is used as a single-family house. It is a single-story, detached building, found in the rural and suburban areas of the province of San Juan. This traditional type of construction is built with adobe walls and no cornice. The traditional adobe house has a range of deficiencies: weak connections, heavy roofs, adobe blocks that deteriorate (especially at the base of the walls) due to prolonged exposure to humidity. This housing type is expected to perform poorly in earthquakes.

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Report #161: Confined and Internally Reinforced Concrete Block Masonry Building

by Diego Velasquez Jofre, Lars Abrahamczyk, Jochen Schwarz

The February 1976 earthquake caused severe damage to housing and buildings in Guatemala. Because many adobe houses were destroyed during the earthquake, there was greater interest in building with reinforced concrete block masonry structures after the event. This building type can now be found throughout Guatemala. Reinforced concrete block masonry structures are primarily used for family housing, both in cities and in rural Guatemala. The main load-bearing elements are masonry walls with concrete block walls reinforced with vertical and horizontal reinforced concrete elements in addition to internal steel reinforcement bars placed in the hollow cores of the concrete blocks. After the 1976 earthquake several guidelines were published on the construction of masonry block buildings, but the first formal standard/code was established in 2000, the Recommended Structural Standards of Design for the Republic of Guatemala -AGIES. The main parameters for structural design are incorporated in chapter No. 9  Mamposteria Reforzada. Nowadays reinforced concrete block masonry houses are constructed all over the country by governmental institutions for low-income classes. Currently this type of structure is the most widely built in Guatemala.

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Report # 160 : Combined and Confined Masonry Construction

by Arturo Tena-Colunga, Artemio Juárez-Ángeles, Victor Hugo Salinas-Vallejo

It is defined as combined and confined masonry structures those where the bearing/seismic walls are made by alternating courses of lightweight concrete blocks (inexpensive in Mexico) with courses of fired clay bricks (more expensive) and they are confined with cast-in place reinforced-concrete tie-beams and tie-columns (Figure 1). The impact of confining elements in masonry walls includes: a) enhancing their stability and integrity for in-plane and out-of-plane earthquake loads, b) enhancing their strength (resistance) under lateral earthquake loads and, c) reducing their brittleness under earthquake loads and hence improving their earthquake performance. Although combined masonry construction has historical background in Mexico and worldwide (i.e., Tena-Colunga et al. 2009), combined and confined masonry became popular in recent times by the initiative of the inhabitants of the central Mexican states of Puebla, Tlaxcala and Oaxaca. This modern version of combined and confined masonry has been used since the early 1990s. Different arrangements to combine and alternate brick courses with block courses have been used (Juárez-Angeles 2009, Salinas-Vallejo 2009), but the one that it is most commonly used is the one depicted in Figure 1, where three courses of clay bricks alternate with a course of concrete blocks. Usually, this type of construction is being used for housing in rural and urban regions of Mexico, but it has also being used for warehouses and apartment buildings up to three stories high. The most common floor systems used with combined and confined masonry are: a) cast-in-place reinforced-concrete slabs 10 to 12 cm thick and, b) precast beams with concrete block infill and concrete topping (cast-in-place) and, c) cast-in-place waffle flat slab with polystyrene infill. Because of the poor quality of the concrete blocks produced in the central regions of Mexico, combined and confined masonry walls have similar behavior but lower shear strength and ductility compared to traditional confined masonry walls made of fired clay bricks only (Tena-Colunga et al. 2009). Nevertheless, these structures have had good performances during moderate and strong earthquakes, such as the M=6.5 June 15, 1999 Tehuacán earthquake and the M=7.6 January 21, 2003 Tecomán earthquake.

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Report # 156 : Typical Single-Story Residential Construction Practices in Trinidad and Tobago

by Richard P. Clarke, Rakesh Ramnath

Typical single-story residential construction in Trinidad and Tobago comprises 100 mm thick unreinforced clay tile or concrete block masonry (URM) load-bearing walls supporting the roof. The roofing is a 20 to 30 degree gable or hipped shape and is of approximately 0.2 to 0.5 kN/m2 in weight. It comprises galvanized steel sheets supported by timber laths or cold-formed steel Z-purlins, in turn supported by timber or structural steel rafters. The rafters are nailed or bolted to the top of the walls, without blocking between the rafters. The flexible roof cannot act as a diaphragm. The soil class ranges from IBC classes B to E. Given the significant seismic hazard for Trinidad and Tobago, (i.e. rock PGA in the range of 0.2g to 0.6g for 10% exceedance probability in 50 years), this form of residential construction is quite vulnerable.

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Report # 148 : Vivienda de Minifalda (Wooden houses with heavy bases)

by Dominik Lang, Alvaro Amador, Lisa Holliday, Claudio Romero L, Armando Ugarte

The term ‘minifalda’, translated ‘miniskirt’ refers to the building’s walls which consist of masonry or concrete in the lower part, while the upper part is made of a light wood construction (also ‘madera y concreto’). According to a recent population census carried out in 2005 (INEC, 2006), the total percentage of minifalda houses in Nicaragua was around 7% (8% in urban and 5.6% in rural areas). In the year 1998, minifalda represented 9.8% of the total houses in Nicaragua (12.8% in urban and 6.1% in rural areas; according to OPAS, 2001). Comparing the two numbers, it shows that the rate of this construction type on the total building stock in Nicaragua has reduced considerably. The combination of a more stable and consolidated base made of concrete or masonry and a light and flexible upper part of the walls made of wood frame construction, provides these houses with some advantages. However, the heavy roofs, which consist mostly of tiles, increase the vulnerability of the buildings especially during earthquake action.

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Report # 144 : Vivienda de Adobe (adobe brick houses)

by Dominik Lang, Lisa Holliday, Omar G. Flores Beleton

Buildings made of adobe brick masonry can still be found in all parts of Guatemala both in rural and urban areas. Generally adobe houses are characterized by only one story, no basement, and sometimes an irregular plan shape. The main use is residential or small commercial (retail trade) purposes. In the 1970’s adobe buildings represented the prevalent construction type in the Republic of Guatemala with a share of more than 39 %. More than half of these buildings (54.3 %) were located in rural settlements, while the rest (45.7 %) was located in urban areas, e.g. Guatemala City (Marroquin and Gándara, 1976). Surprisingly, the percentage of adobe buildings at that time was higher in urban areas than in rural regions. Today, circumstances have changed and adobe structures prevail in rural areas while only remainders of this traditional construction technique can be found in the cities. Based on a more recent statistical survey in the municipality of Guatemala City conducted by ASIES (2003), around 4 % of the building stock is either adobe or bahareque buildings. The latter not being covered in the present report. Throughout the report, a distinction is made between adobe buildings in rural (Figure 1) and urban (Figure 2) areas. This distinction affects some of the building parameters and features herein.

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Report # 141 : Vivienda de Bahareque

by Dominik Lang, Roberto Merlos, Lisa Holliday, Manuel A. Lopez M.

The bahareque construction type refers to a mixed timber, bamboo and mud wall construction technique which was the most frequently used method for simple houses in El Salvador before the 1965 earthquake (Levin, 1940; Yoshimura and Kuroki, 2001). According to statistics of the Vice-ministry of Housing and Urban Development in the year 1971 bahareque buildings had a share of 33.1 % of all buildings in El Salvador, while in 1994 the percentage of bahareque declined to about 11 % (JSCE, 2001b) and in 2004 to about 5 % (9 % in rural areas; according to Dowling, 2004). The term ‘bahareque’ (also ‘bajareque’) has no precise equivalent in English, however in some Latin American countries this construction type is known as ‘quincha’ (engl.: wattle and daub). In order to prevent confusion it should be noted, that in El Salvador the term ‘bahareque’ is used for all types of this mixed construction type regardless the material of the horizontal elements (struts).

Bahareque buildings are characterized by high flexibility and elasticity when carefully constructed and well-maintained, and thus originally display good performance against dynamic earthquake loads. However, bahareque buildings in most cases show high vulnerability during earthquakes. This is caused by poor workmanship (carelessness and cost-cutting measures during construction), lack of maintenance (resulting in a rapid deterioration of building materials), and structural deficiencies such as a heavy roofing made out of tiles. Bahareque structures are primarily of residential use and only one story. The structural walls are mostly composed of vertical timber elements and horizontal struts which are either made of timber slats, cane/reed (carrizo), bamboo (vara de castilla, caña brava or caña de bambú) or tree limb (ramas). These members are generally 2- to 3-inches thick and are fastened at regularly spaced intervals from the base to ceiling height at the vertical elements (with nails, wires or vegetal fibers). This creates basketwork type skeleton which is then packed with mud and clay filler combined with chopped straws (or sometimes with whole canes), and covered with a plaster finish in some cases. In rural areas, the walls are often left plane, without any lime plaster and whitewash, or paint, which gives them a wavy surface with an unfinished character. It should be noted that bahareque houses in rural areas are quite different from those in urban areas both in terms of their esthetical appearance as well as their structural capacity (cf. Figures 1 and 2).

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Report # 137 : Adobe walls supporting rough timber framed roof with corrugated iron sheeting.

by Matthew A. French

The plan of this adobe building is a simple rectangle with three rooms. Adobe as a material is very weak under seismic loads, which is the main issue which concerns this building type. Also, the roof does not have sufficent eaves to protect the adobe walls, which has resulted in the dislodging of the exterior plaster. This has erroded the walls, further reducing their structural strength. Adobe is commonly used in Nicaragua, as it is both affordable and accessible, but it is being replaced by more ‘modern’ materials, such as concrete block and red fired brick.

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Report # 136 : Adobe with sawn timber roof framing and corrugated iron sheeting

by Matthew A. French

This very small building doubles as a home and workplace. The homeowner weaves products such as hats, clothes and mats for a living. The building functions as a showroom for her products by the day and as her house for rest at night. Three months before the site visit, the house was washed away by Hurricane Stan that hit the Central American region. Massive rainfall led to landslides in the Lago Antilian area, where the site is located. Her house was destroyed and this is the new one constructed. This case study is characteristic of new adobe construction in the Guatemala today. Timber dowels at the top brick course help to secure the ring beam or timber roof framing to the walls. For economic reasons, the roof is corrugated iron, but the long-term plan is to place clay tiles directly over top for their thermal and aesthetic properties. This case study is testament to the trying and tenuous living conditions which the occupants face. It demonstrates that even though un-reinforced adobe fails, many have no option but to replace it with structurally fragile adobe once more.

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