Clay brick/concrete block masonry walls with concrete floors (predating seismic codes or with a few seismic features), Colombia

From World Housing Encyclopedia

1. General Information

Report: 12

Building Type: Clay brick/concrete block masonry walls with concrete floors (predating seismic codes or with a few seismic features)

Country: Colombia

Author(s): Luis Gonzalo Mejia

Last Updated: 6/17/2003

Regions Where Found: Buildings of this construction type can be found in Colombia. It represents approximately 50% of the existing housing stock of medium rise buildings (4- to 6-story high). This type of housing construction is commonly found in urban areas. Majority of buildings of this type found in rural areas are 1- and 2-story high.

Summary: Typical multi-family housing construction found in urban areas of Colombia. It is a modern construction practice and represents approximately 50% of the housing stock for medium-rise (4- to 6-story high) buildings constructed in the last 25 years. This type of construction generally predates seismic codes, however some buildings of this type were constructed after the first edition of the Colombian Seismic Code was issued in 1984. This type of construction can be found either on flat or on sloped terrain; vertical stiffness irregularity in the sloped terrain conditions may introduce additional unfavorable effects. Due to poor construction practices and poor detailing of reinforcement, this construction is considered to be very vulnerable to earthquake effects.

Length of time practiced: Less than 25 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 5-9 units

Typical number of stories: 5

Typical story Height: 2.6 meters

Are buildings of this type typically built on flat or sloped terrain? Both


2. Features

Plan Shape: Square, solid; Rectangular, solid

Building Configuration: Typically, a square plan (4 flats per floor) or a rectangular plan (2 flats per floor).

Typical plan length (meters): 17

Typical plan width (meters): 17

Typical story height (meters): 2.6

Lateral Load Resisting System: This is a bearing wall system, wherein the walls provide stiffness for in-plane lateral loading and stability to resist lateral loads (wind and seismic effects). Floor slabs are either 100 mm thick R.C. slabs or different types of slab and joist floors; in some cases, slabs with concrete joists and tile blocks are used. The roof is normally made from rafters, sheathing roofing felt and asbestos-cement tile or R.C. slab. Floor slab can act as a rigid diaphragm; the same is not true for the wooden roof because a continuous R.C. beam (bond beam) atop the walls is often absent.

Gravity Load Bearing System: The walls carry both lateral and gravity loads down to the R.C. strip foundation. In poor soil conditions, pile foundations are used because of the great susceptibility to settlement of the bearing walls. It is important to mention that the slabs span normally in one direction so the walls in one direction sustain gravity and lateral loads and the walls in the cross direction carry lateral loads only.

Type of Structural System: Masonry: Unreinforced Brick Masonry Walls: Unreinforced brick masonry in lime/cement mortar; Masonry: Concrete block masonry walls: Unreinforced in lime cement or mortar2

Comments on type of structural system: Most buildings of this construction are brick masonry in lime/cement mortar or clay brick/tile masonry, with wooden posts and beams; however, some buildings are concrete block masonry in cement mortar or clay brick masonry, with concrete posts/tie columns and beams.

Typical span: 3.0 meters

Typical wall density: 6% to 8.5%

Wall Openings: Information about the openings in a typical median building is summarized: Number of openings Size (sq m): 7 at 2.0 sq m; Doors Windows Facade: 5 0 1.80; Opening area/wall area: 30%; Position of opening: Between 0.5 and 1.0m from corners. 3

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Means of Escape: Usually building does not have additional means of escape.

Modifications of buildings: There are not many modifications in this building type. The most typical modification pattern observed is demolition of interior walls.

Type of Foundation: Shallow Foundation: Reinforced concrete strip footing; Deep Foundation: Reinforced concrete bearing piles; Deep Foundation: Reinforced concrete skin friction piles

Additional comments on foundation: In some Colombian cities e.g. Bogota, deep foundations are mandatory in a typical case. However, in other cities e.g. Medelin, R.C. strip footings are normally used.

Type of Floor System: Cast-in-place or precast solid slabs

Additional comments on floor system: The floor is considered to be a rigid diaphragm that transfers the loads to the wall, although in many instances the floor-to-wall connections are deficient.

Type of Roof System: Timber: wood planks or beams that support slate metal asbestos-cement or plastic corrugated sheets or tiles

Additional comments on roof system: The roof is considered to be a flexible structure.

Additional comments on siting: This type of construction is found on flat terrain (in the coastal areas) and in the continental region (the Andean) on the sloped and occasionally very steep terrain. When separated from adjacent buildings, the typical distance from a neighboring building is 10 meters.

3. Building Process

Description of Building Materials

Structural Element Building Material (s) Characteristic Strength Mix Proportions and Dimensions Comment (s)
Wall/Frame Concrete block masonry walls f'm = 10.0 MPa w/h/l 150 x 200 x 400 mm 120 x 200 x 400 mm N/A
Wall/Frame Clay Brick masonry wall f'm = 3 - 10.0 MPa w/h/l 200 x 100 x 400 mm 200 x 150 x 400 3MPa for unreinforced or confined masonry and 10MPa for masonry with interior reinforcement
Wall/Frame Cement Mortar Cement grout f'm = 5 - 10.0 MPa Cement : Sand1:6 to 1:4 Better strengths for buildings with vertical reinforcement, because they have some seismic features. 10.0 MPa 1:4 For walls with vertical reinforcement
Foundations Reinforced concrete f'c = 20.0 MPa 1 : 2 : 3 Cement/sand/aggregates
Floors R.C. slabs or hollow tile 10.0 # 20.0 MPa 1:3:5 →1:2:3 Cement/sand/aggregates
Roof Abarco (Cariniane piriformis) 9.0 MPa 50 x 100 mm Whenever the roof is in R.C. properties are the same as floors.

Design Process

Who is involved with the design process? Engineer, Architect, Other

Roles of those involved in the design process: Whenever engineered, this construction type is built for speculation purposes.

Expertise of those involved in the design process: Architects and engineers participate in the design of buildings of this type built for inhabitants belonging to the middle economic class. However, architects and engineers are not involved in the informal construction developed in areas inhabited by poorer sections of the society. If engineers and architects are involved in the construction, there is a “resident” (architect or engineer) on the site during the construction. Unfortunately, he/she is concerned mainly with the project cost aspects (rather than with the construction quality). Engineers and architects do not play any role in informal projects developed for poor people.

Construction Process

Who typically builds this construction type? Other

Roles of those involved in the building process:

Expertise of those involved in building process: The masons involved in the construction are usually skilled and semi-skilled.

Construction process and phasing: This is a typical construction process: firstly, the terrace is formed, followed by the construction of strip foundation. Subsequently, walls, slabs and roof are built, and the masons are skilled or semi-skilled. No equipment is used except for the simple tools. Normally, buildings of this type are built by a developer (in some cases by the owner).

Phasing of Construction: The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size. The above statements are true, except for the case of informal construction.

Construction issues:

Building Codes and Standards

Is this construction type address by codes/standards? Yes

Applicable codes or standards: 1984: Colombian code for earthquake resistant buildings CCCSR-84. 1998: Colombian code for earthquake resistant design and construction of buildings NSR-98 Prior to 1984, the ACI and UBC codes were widely used.

Year the first code/standard addressing this type of construction issued: 1984

When was the most recent code/standard addressing this construction type issued? 1998

Process for building code enforcement: After an earthquake, the authorities enforce the use of building codes, however shortly thereafter these regulations are not enforced with an adequate effort.

Building Permits and Development Control Rules

Are building permits required? Yes

Is this typically informal construction? No

Is this construction typically authorized as per development control rules? Yes

Additional comments on building permits and development control rules: Some of these buildings, especially those of unreinforced masonry construction or confined masonry are informal construction.

Building Maintenance and Condition

Typical problems associated with this type of construction: As the amount of reinforcement is it rather limited (and in some cases does not exist at all), and the quality of materials and workmanship is generally poor, this construction type is very susceptible to earthquake effects.

Who typically maintains buildings of this type? Owner(s)

Additional comments on maintenance and building condition:

Construction Economics

Unit construction cost: On the average $300,000 Colombian pesos/ sq m ($US 150 /sq m)

Labor requirements: It is possible to construct one floor per month on the average (when the building is designed for its final size and engineers/architects participate in the construction).

4. Socio-Economic Issues

Patterns of occupancy: Normally one family occupies one housing unit. On the average, 5 floors per building; consequently, there are 20 units in buildings of a square plan (four apartments per floor), and 10 units in buildings of a rectangular plan (two apartments per floor).

Number of inhabitants in a typical building of this construction type during the day: 5-10

Number of inhabitants in a typical building of this construction type during the evening/night: >20

Additional comments on number of inhabitants:

Economic level of inhabitants: Low-income class (poor), house price to annual income ratio 10000/1500; Middle-income class, house price to annual income ratio 40000/6000

Additional comments on economic level of inhabitants: The above are average values. House price for middle class section ranges from US$ 30,000 to 50,000. The approximate economic distribution of population in Colombia is as follows (Economic status (%), Annual Income): Very poor 35%, <1000; Poor 35% 1000-2000; Middle Class 25% 2000 -10000; High Middle Class 4% 10000 - 40000; Rich 1% >40000. Economic Status: For Poor Class the Housing Price unit is 10000 and the Annual Income is 1500. For Middle Class the Housing Price unit is 40000 and the Annual Income is 6000.

Typical Source of Financing: Combination

Additional comments on financing: The main source of financing for the poor people is informal network (friends and relatives) and (sometimes) small lending institutions. For the middle class population, the main sources of financing are personal savings and commercial banks.

Type of Ownership: Rent, Own outright, Own with debt (mortgage or other), Units owned individually (condominium)

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: Yes

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: No

Additional comments on insurance: Earthquake insurance is available only for engineered buildings. At the present time, premium discounts are not available for seismically strengthened buildings, however the insurance companies are dealing with this matter.

What does earthquake insurance typically cover/cost: Although there are many unclear aspects in this matter, in general the insurance covers the previously fixed value of the building. The insurance cost varies from 0.1 to 0.15% of the building value.

5. Earthquakes

Past Earthquakes in the country which affected buildings of this type

Year Earthquake Epicenter Richter Magnitude Maximum Intensity
1979 4.8N, 76.2W, depth: 108 km(Mistrato) 6.7 Ms VIII MMI (MANIZALES)
1983 2.46N, 76.69W, depth: 22 km (Popayan) 5.5 Mb IX MMI (Popayan)
1995 4.1N, 76.62W, depth: 73 km (Pereira) 6.4 Mw VIII MMI (PEREIRA)
1999 4.46N, 75.72W, depth: 17 km (Armenia) 6.0Ms IX MMI (ARMENIA)

Additional Comments: Typical earthquake damages are illustrated in Figures 7-13.

Structural and Architectural Features for Seismic Resistance

The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.

Structural/Architectural Feature Statement Seismic Resistance
Lateral load path The structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation. FALSE
Building Configuration-Vertical The building is regular with regards to the elevation. (Specify in 5.4.1) TRUE
Building Configuration-Horizontal The building is regular with regards to the plan. (Specify in 5.4.2) TRUE
Roof Construction The roof diaphragm is considered to be rigid and it is expected that the roof structure will maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area. FALSE
Floor Construction The floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) will maintain its integrity during an earthquake of intensity expected in this area. TRUE
Foundation Performance There is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-Redundancy The number of lines of walls or frames in each principal direction is greater than or equal to 2. TRUE
Wall Proportions Height-to-thickness ratio of the shear walls at each floor level is: Less than 25 (concrete walls); Less than 30 (reinforced masonry walls); Less than 13 (unreinforced masonry walls); FALSE
Foundation-Wall Connection Vertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation. TRUE
Wall-Roof Connections Exterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. TRUE
Wall Openings N/A
Quality of Building Materials Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). FALSE
Quality of Workmanship Quality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards). FALSE
Maintenance Buildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber). FALSE
Other Insufficient reinforcement for diaphragm action

Additional comments on structural and architectural features for seismic resistance: Foundation Performance: Occasionally, there are buildings with induced weaknesses caused by foundation movements (please see Figure 12). Wall-Roof connections: See Additional Comments in Section titled “Type of floor/roof system”.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: -Unreinforced or with insufficient vertical and horizontal reinforcement. - Stepped construction (offsets) for example half of the buildings with six stories and the other half with five due to the sloping terrain (resulting in no uniform vertical stiffness distribution).

Earthquake-resilient features in walls: N/A

Seismic deficiency in frames: N/A

Earthquake-resilient features in frame: N/A

Seismic deficiency in roof and floors: - Absence of continuous boundary members, chords and collectors. -Weak roof-wall and floor-wall connections.

Earthquake resilient features in roof and floors: N/A

Seismic deficiency in foundation: -Poor quality of workmanship and materials. -Foundations designed only for vertical loads without considerations for overturning moments.

Earthquake-resilient features in foundation: N/A

Additional comments on seismic features: For the illustration of seismic deficiencies please see Figures 1-6.

Seismic Vulnerability Rating

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

High vulnerabilty Medium vulnerability Low vulnerability
Seismic vulnerability class < o >

Additional comments on seismic vulnerability: 0 - probable value, < - lower bound, > - upper bound

6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening
Walls -Unreinforced or with insufficient vertical and horizontal reinforcement. - Stepped construction (offsets) for example half of the buildings with six stories and the other half with five due to the sloping terrain (resulting in nonuniform vertical stiffness distribution). See Additional Comments
Roof and floors: - Absence of continuous boundary members, chords and collectors. -Weak roof-wall and floor-wall connections. See Additional Comments
Other : -Poor quality of workmanship and materials. -Foundations designed only for vertical loads without considerations for overturning moments. See Additional Comments

Additional comments on seismic strengthening provisions: Due to the fact that this construction type in general belongs to poor or middle class population, the costs of seismic strengthening is so prohibitive and unaffordable; this is a major reason for a very limited experience in this area. For the above reason, only scarce efforts have been made in the area of seismic strengthening. As illustrated in Figures 24 and 25, an appropriate seismic strengthening technique includes the installation of new end confining members in the selected walls. An alternative seismic strengthening technique that would be appropriate for buildings of this type (using the Fiber Reinforced Polymers) is very expensive.

Has seismic strengthening described in the above table been performed? No

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? N/A

Was the construction inspected in the same manner as new construction? N/A

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? N/A

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? N/A

7. References

  • 1. Normas Colombianas de y construccion Sismo Resistente (NSR-98)


Name Title Affiliation Location Email
Luis Gonzalo Mejia Consulting Structural Engineer L.G.M y Cia. Calle 49b #77b #12 Medellin Colombia


Name Title Affiliation Location Email
Sergio Alcocer Director of Research Circuito Escolar Cuidad Universitaria, Institute of Engineering, UNAM Mexico DF 4510, MEXICO
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