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:

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

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments:

Plan Shape: Square, solidRectangular, solid

Additional comments on plan shape: 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

Type of Structural System: Masonry: Unreinforced Masonry Walls: Brick masonry in lime/cement mortarMasonry: Unreinforced Masonry Walls: Concrete block masonry in cement mortar

Additional comments on structural 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. 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 & lateral load-resisting systems: 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 wall densities in direction 1: 5-10%

Typical wall densities in direction 2: 5-10%

Additional comments on typical wall densities: The typical structural wall density is 6% to 8.5%.

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

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

Modifications of buildings: There are no 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 footingDeep Foundation: Reinforced concrete bearing pilesDeep Foundation: Reinforced concrete skin friction piles

Additional comments on foundation: It consists of reinforced concrete end-bearing piles and reinforced concrete skin-friction piles. 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 beamless reinforced concrete floorOther floor system

Additional comments on floor system: Other: Structural concrete cast-in-place flat slabs, precast solid slabs 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: Roof system, other

Additional comments on roof system: Other: Timber wood planks or beams that support slate, metal, asbestos-cement or plastic corrugated sheets or tiles; wood planks or beams supporting natural stones slates The roof is considered to be a flexible structure.

Additional comments section 2: 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.

Who is involved with the design process? EngineerArchitectOther

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.

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). 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:

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.

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.

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.

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:

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).

Additional comments section 3:

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)Middle-income class

Additional comments on economic level of inhabitants: Ratio of housing unit price to annual income: 5:1 or worse 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: RentOwn outrightOwn with debt (mortgage or other)Units owned individually (condominium)

Additional comments on ownership:

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

What does earthquake insurance typically cover/cost: 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. 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.

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

Additional comments on premium discounts:

Additional comments section 4:

Damage patterns observed in past earthquakes for this construction type: Typical earthquake damages are illustrated in Figures 7-13.

Additional comments on earthquake damage patterns:

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.

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 Sections 2.10 & 2.11 #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 nonuniform vertical stiffne

Earthquake-resilient features in walls:

Seismic deficiency in frames:

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors: #NAME?

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:

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

Additional comments section 5:

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

Additional comments section 6:

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