Construction practices

Common buildings classes

In most Central American urban centres (except for Panama City), high-rise construction is still a minor fraction of the building stock and most households are individual low-rise structures. The Central American Centre for Prevention of Natural Disasters (CEPREDENAC) lists adobe, unreinforced masonry, confined masonry, and reinforced masonry made of concrete blocks as the most widely used types of construction. The World Housing Encyclopedia (WHE) has reports that include information concerning building materials, architectural traits, construction process, socio-economic environment and even the expected seismic performance of these structures. There are 14 reports covering several building classes. Reinforced concrete frames and timber structures are commonly found in urban and rural areas of Belize and Panama (Redmond et al. 2012). For Guatemala, Honduras and Nicaragua, there are entries covering adobe and masonry construction, which accounts for a significant fraction of the building stock in these countries and represents one of the most vulnerable types of construction (e.g. Lang et al. 2007; French et al. 2007). Adobe and bahareque (wattle-daub) can also be found in El Salvador, whereas for Costa Rica this type of construction is prohibited and therefore few constructions remain at present, with most of the residential building stock being composed by confined masonry and wooden structures (Calderon and Silva 2018). Wood is widely used in the Caribbean for residential and commercial purposes as well. Moreover, the urban centres are more densely populated than their Central American counterparts (e.g. La Habana, Santiago de Cuba and Santo Domingo), and consequently mid-rise and high-rise masonry and concrete structures are more common. The use of heavier buildings, commonly roofed with concrete slabs, is frequent in Cuba, Haiti and the Dominican Republic, where tropical storms are a great concern (ONE Cuba 2016, Lallemant 2015, ONE Dominican Republic 2016).

Therefore the main identified structure types include reinforced concrete bare frames, infilled concrete frames, concrete walls, wood panels, adobe walls, unreinforced masonry, confined masonry, reinforced masonry and steel bare and braced frames. Since wattle-daub and waste materials are forms of informal construction, these buildings were classified together in a single class. The following table summarizes the main structural types and their lateral load resisting system. Each class is identified with a string following the GEM Building Taxonomy (Brzev et al. 2013).

Structure type	Taxonomy	Occupancy Use
Reinforced concrete bare frames	CR/LFM	Residential, commercial and industrial
Infilled concrete frames	CR/LFINF	Residential and commercial
Concrete walls	CR/LWAL	Residential, commercial and industrial
Wood panels	W+WLI/LWAL	Residential and Commercial
Informal	UNK	Residential
Adobe walls	ADO/LWAL	Residential
Unreinforced masonry	MUR/LWAL	Residential, commercial and industrial
Confined masonry	MCF/LWAL	Residential, commercial and industrial
Reinforced masonry	MR/LWAL	Residential, commercial and industrial
Steel bare frames	S+SR/LFM	Commercial and industrial
Steel braced frames	S+SR/LFBR	Commercial and industrial

Characterization of the building stock

These structural types were further characterized into specific classes by adding two more attributes: the building height and the expected level of ductility. Regarding height (i.e. number of storeys), all of the household censuses adopt a separation of dwellings into individual houses (low rise structures holding only one family) and apartment buildings (mid and high-rise structures that hold more than one dwelling). According to this information, individual houses of adobe, masonry, engineered wood and informal construction were considered herein to have 1 to 3 storeys. Apartment dwellings of masonry, reinforced concrete and steel are assumed to range from 3 to 12+ storeys. Concerning the possible ductility categories, dwellings made of adobe, wattle-daub, stone and waste materials were all classified as non-ductile. The assumption is that these structures would perform poorly regardless of the date of construction, building practices, structural system and material quality. On the other hand, reinforced concrete, confined masonry, reinforced masonry and steel frames represent typologies that can range from low, medium and high ductility. The different combinations of structure types, height and ductility levels resulted in 73 building classes. Each class has the capacity to hold one or more dwellings. The following table presents the main attributes of the building classes, following the GEM Building Taxonomy.

Structure type	Taxonomy string	LLRS	Ductility	Storeys	Capacity
Wood panels	W+WLI/LWAL+DNO	Panels	Very Low	1 to 2	1
Wood panels	W+WLI/LWAL+DUM	Panels	Moderate	1 to 2	1
Informal	UNK	Waste materials	Low	1	1
Unreinforced masonry	MUR/LWAL+DNO	Wall	Very Low	1 to 2	1
Unref. Masonry	MUR+ADO/LWAL+DNO	Wall	Very Low	1 to 2	1
Reinforced Masonry	MR/LWAL+DLO	Wall	Low	1 to 3	1 to 2
Reinforced Masonry	MR/LWAL+DUM	Wall	Moderate	1 to 3	1 to 2
Reinforced Masonry	MR/LWAL+DUH	Wall	High	1 to 3	1 to 2
Confined Masonry	MCF/LWAL+DLO	Wall	Low	1 to 3	1 to 2
Confined Masonry	MCF/LWAL+DUM	Wall	Moderate	1 to 3	1 to 2
Confined Masonry	MCF/LWAL+DUH	Wall	High	1 to 3	1 to 2
Reinforced concrete	CR/LFM+DLO	Bare frame	Low	1 to 2	1 to 2
Reinforced concrete	CR/LFM+DLO	Bare frame	High	3 to 4	2 to 6
Reinforced concrete	CR/LFM+DLO/SOS	Bare frame	Low	2	1
Reinforced concrete	CR/LFINF+DLO/SOS	Infilled frame	Low	2	1
Reinforced concrete	CR/LFINF+DLO	Infilled frame	Low	1 to 3	1 to 2
Reinforced concrete	CR/LFINF+DUM	Infilled frame	Moderate	1 to 3	1 to 2
Reinforced concrete	CR/LFINF+DUH	Infilled frame	High	1 to 3	1 to 2
Reinforced concrete	CR/LFINF+DUH	Infilled frame	High	4 to 6	2 to 15
Reinforced concrete	CR/LDUAL+DUH	Wall & Frame	High	6 to 12	10 to 68
Steel	S+SR/LFBR+DUM	Braced Frame	Moderate	1	1
Steel	S+SR/LFBR+DUH	Braced Frame	High	6 to 12	10 to 68
Steel (Cold formed)	S+SL/LFM+DLO	Frame	Low	1	1
Steel	S+SR/LFM+DLO	Frame	Low	1	1
Steel	S+SR/LFM+DUM	Frame	Moderate	1	1
Steel	S+SR/LFM+DUH	Frame	High	1	1

Mapping schemes

The development of the exposure model requires distributing the dwellings and establishments amongst the building classes previously identified. This was achieved following the methodology proposed by Yepes-Estrada et al. (2017). With this approach, an algorithm is used to segregate dwellings in a database into groups according to a number of census variables (e.g. wall material, floor material, roof material, household type). The dwellings within each group are then distributed among building classes following a set of criteria called a mapping scheme. It is based on engineering judgement, local expertise and socio-economic indexes to ensure a proper characterization of the building environment in each administrative division.

To provide an example, when analysing dwellings in the municipality of Nueva San Salvador (see the following figure), the algorithm assigns first three geographical tags to the dwellings, namely Country: El Salvador; Department: San Salvador; Municipality: San Salvador (i.e. the administrative levels in El Salvador). Then, it groups the dwellings using variables provided by the database, such as type of household (i.e. individual house or inside an apartment building), the type of floor (e.g. ceramic or concrete) and the wall material (e.g. masonry, wood, adobe). The number of dwellings in each group are distributed among classes based on the criteria for that group. For example, regardless of the floor material, roof material and household type, dwellings with walls made of adobe were located into the MUR+ADO structure type. Given the nature of such construction practice, they were assigned a low level of ductility, represented by the DNO string. Furthermore, given that these dwellings are registered as individual houses, they are classified as single buildings that can have 1 or 2 storeys (taxonomy strings H1 or H2). Consequently, dwellings in that group were assigned to building classes MUR+ADO/LWAL+DNO/H1 or MUR+ADO/LWAL+DNO/H2.

A significant percentage of households in Central America and the Caribbean have walls made of concrete masonry blocks. Because census enquirers may lack engineering knowledge, this group could include structures of unreinforced masonry, reinforced masonry, confined masonry or even concrete frames with masonry infills. Moreover, in such cases, dwelling quality or ductility cannot be inferred by the construction material alone. Thus, the selection criteria had to be complemented with additional information. For example, when dwelling groups presented masonry walls and cement floors, they were subdivided into low quality masonry classes (i.e. one storey unreinforced masonry and low ductility reinforced masonry). On the other hand, dwellings that presented masonry walls and mosaic or ceramic finished floors were distributed amongst reinforced masonry, confined masonry and reinforced concrete classes. The percentage of dwellings that gets assigned to each class and ductility category depends on two country specific factors: the seismic code rating, and the level of code compliance, which are discussed in the following section.