Reinforced clay/concrete block masonry building, Chile

From World Housing Encyclopedia


1. General Information

Report: 5

Building Type: Reinforced clay/concrete block masonry building

Country: Chile

Author(s): Ofelia Moroni, Cristian Gomez, Maximiliano Astroza

Last Updated:

Regions Where Found: This housing type is used throughout Chile. Between 1992 and 2002 this type of building represented about 7% of the total social dwellings (Jaramillo, 2011). This housing type is used throughout Chile. Between 1992 and 2002 this type of building represented about 7% of the total social dwellings (Jaramillo, 2011).

Summary: This is a rather recent construction practice followed since 1970s, and it has been widely used for dwellings and up to 4-story high apartment buildings. Buildings of this type can be found both in urban and rural areas of Chile. The main load-bearing elements are masonry walls reinforced with vertical steel reinforcement bars placed in the hollow cores of clay masonry units (hollow clay tiles) or concrete blocks. Horizontal reinforcement bars are placed in horizontal bed joints. Masonry shear walls are tied together at floor levels by means of reinforced concrete beams, in a regular structural layout. Stiffness distribution both in plan and elevation is uniform.Prior to 1986 there was no seismic design code for this structural type. During the March 3, 1985 Llolleo earthquake, performance of buildings of this type was rather poor, mainly due to construction problems, such as partial grouting in the hollow cores with reinforcement, poor quality of the mortar, and lack of horizontal reinforcement. Following the earthquake, the Chilean Design Code NCh1928 code was published based on the U.S. Uniform Building Code (UBC-1979) and the seismic performance of this construction type reported in previous earthquakes. Since 1993, when NCh1928.Of93 was published, and more restricted requirements were enforced, the use of this type of construction has been less frequent, in part due to economic reasons.

Length of time practiced: 25-60 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 10-19 units

Typical number of stories: 2-4

Terrain-Flat: Typically

Terrain-Sloped: Occasionally

Comments: Construction practice followed in the last 40 years. Due to economic reasons its use for social dwellings has declined in the la


2. Features

Plan Shape: Rectangular, solid

Additional comments on plan shape:

Typical plan length (meters): 12-30

Typical plan width (meters): 5-8

Typical story height (meters): 2.3

Type of Structural System: Masonry: Reinforced Masonry: Clay brick masonry in cement mortarMasonry: Reinforced Masonry: Concrete block masonry in cement mortar

Additional comments on structural system: Gravity load bearing and Lateral load-resisting system: The main load-bearing elements are masonry walls reinforced with vertical steel reinforcement bars placed in the hollow cores of clay masonry units (hollow clay tiles) or concrete blocks. Horizontal reinforcement bars are placed in horizontal bed joints. Although the cores and voids containing reinforcement should be filled with grout, this is not always done. Most of the time cores and voids are filled only with the same mortar used in the horizontal joints. In addition, the size of the hollow in the ceramic unit is quite small so it is difficult to fill it. Concrete blocks, mostly used in the northern part of Chile, have larger hollow cores, however they are experiencing water leakage problems and since 1997 the use of these blocks has been banned in Central Chile. Masonry shear walls are tied together at floor levels by means of reinforced concrete beams, in a regular structural layout. In most cases, wall layout is symmetrical with regards to at least one axis. Stiffness distribution both in plan and elevation is uniform. The Chilean code for reinforced masonry building specifies the size and the minimum quantity of vertical and horizontal bars that must be used in a reinforced masonry walls. The sum of the areas of horizontal and vertical reinforcement shall be at least 0.0015 times the gross-sectional area of the wall and the minimun area of reinforcement in either direction shall not be less than 0.0006 times the gross cross-sectional area of the wall. The spacing of reinforcement shall not exceed 120 cm or 6 times the thickness of the wall. The diameter of the vertical reinforcement shall not be less than 8 mm and the horizontal bar shall not exceed 0.5 times the thickness of the horizontal mortar joint.

Gravity load-bearing & lateral load-resisting systems: Walls are made of clay or concrete block masonry.

Typical wall densities in direction 1: 2-3%

Typical wall densities in direction 2: 2-3%

Additional comments on typical wall densities: The total wall area/plan area per unit floor d/n % correlates quite well with observed damage. This index varies between 0.5 and 1.5%. If d/n in longitudinal and transverse direction are different, the smallest value controls the behavior of the building. The unit shear strength may also be considered, so a larger d/n is required for buildings built with concrete blocks. (Jaramillo, 2011).

Wall Openings: In each facade there may be 3 to 4 openings of 0.8 to 1.5 m width probably equally spaced.

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

Modifications of buildings: Typical patterns of modification observed are infill balconies or openings of door in exterior walls

Type of Foundation: Shallow Foundation: Reinforced concrete strip footing

Additional comments on foundation: Usually the foundation does not have reinforcement, unless the soil is clay or silt

Type of Floor System: Other floor system

Additional comments on floor system: Floor system(s): Structural concrete (cast in place solid slabs, precast solid slabs) In the analysis the floor is considered to be a rigid diaphragm.

Type of Roof System: Roof system, other

Additional comments on roof system: Roof system: Timber, wood planks or beams that support slate, metal, asbestos-cement or plastic corrugated sheets or tiles.

Additional comments section 2: Typical separation distance between buildings: 5 meters; Buildings of this type are located close together, conforming what is called “conjuntos”, “poblaciones” or “villas”. They represent several buildings of the same type with some space left for garden or communities activities that most of the time nobody cares about them, ending filled with garbage or at the most as an earth soccer field. In an average, corresponding unit housing area is 40 - 50 m2.


3. Building Process

Description of Building Materials

Structural Element Building Material (s) Comment (s)
Wall/Frame Wall: 1) Clay brick2) Concrete block Wall: 1) Characteristic Strength clay brick : 6-12 MPaDimensions: 14 x 292) Characteristic Strength concrete block: 3-10 MpaDimensions: 19x39x19 or 14x39x9
Foundations
Floors
Roof
Other Concrete H18 Steel A44-28H Characteristic Strength concrete: 18 Mpa Steel strength: 280 Mpa

Design Process

Who is involved with the design process? Owner

Roles of those involved in the design process: The owner of the construction site hires a professional team that includes engineer and architects

Expertise of those involved in the design: The structural engineer has 6 years of studies and more than 3-5 years of experience. The construction engineer has 6 years of studies and less experience than the structural engineer. There is not compulsory inspection during the construction, but when inspection does exist larger masonry compression strength is allowed. Since year 2001 (ley no 19748), peer revision of the structural project is compulsory for buildings taller than 3 story. The designer may visit the construction site once or twice during the construction.


Construction Process

Who typically builds this construction type?: Contractor

Roles of those involved in the building process: In the past, construction companies hired by the state build it. Nowadays, private companies built and sell directly under the supervision of governmental staff.

Expertise of those involved in building process: The expertise is the same stated in 3.2.3

Construction process and phasing: One contractor builds large quantities of this type of building, so project management and control techniques are used in order to increase productivity and to diminish cost. When constructing the vertical reinforcing bars are usually first placed into position before laying the masonry units. Then, the horizontal bars can be placed in horizontal mortar joints. Finally, vertical reinforcement is grouted as the work progresses. With respect to equipment the following is commonly used: concrete mix, trucks, travelling crane, winch, pneumatic cramp.This building is not typically constructed incrementally and is designed for its final constructed size.

Construction issues: Partial grouting in vertical reinforcement. Bending of reinforcement bars Bad reinforcement detailing at the corners or intersection of walls.Insufficient concrete covers for horizontal reinforcement.


Building Codes and Standards

Is this construction type address by codes/standards? Yes

Applicable codes or standards: NCh1928.Of93 Albanileria Armada-Requisitos para el diseno y calculoThe first code/standard addressing this type of construction was issued in 1986, although provisionally dispositions to design this type of buildings existed since 1981. The most recent code/standard addressing this construction was issued in 1993, however at present time it is in a revision process. Applicable national building code, material codes and seismic code/standards: NCh433.Of96 Seismic Design of BuildingsNCh1928.Of93 Albanileria Armada-Requisitos para el diseno y calculoThe first code/standard addressing this type of construction was issued in 1986, although provisionally dispositions to design this type of buildings existed since 1981. The most recent code/standard addressing this construction was issued in 1993, and modified in 2003. Applicable national building code, material codes and seismic code/standards: NCh433.Of96 Seismic Design of Buildings, last modification in 2011

Process for building code enforcement: The building design must follow the NCh433.of96 code (modified in 2011) and NCh1928.of93 (modified in 2003). SERVIU a governmental office in charge of social dwellings has a professional staff to review the projects and to inspect during construction. In case of damage an arbitrage process may take place at the court of justice.


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? No

Additional comments on building permits and development control rules:


Building Maintenance and Condition

Typical problems associated with this type of construction: Concrete blocks buildings have had water ingress.

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

Additional comments on maintenance and building condition: Maintenance is quite low, because inhabitants are low income people


Construction Economics

Unit construction cost: According to Bravo and Martinez (1993) the total cost of this type of building can be blotted out in site 15%, construction cost 40%, urbanization 17%, operating cost 13% and profit 15%.In 2001, the cost of one unit was 200 to 400 UF (area 45 m2), $78.000 to $140.000 /m2 (US$135-US$245/m2).Better quality unit may cost up to $174.000 /m2 (US$300/m2).

Labor requirements: At present, depending on technology used, the construction of several units built simultaneously may take 2-3 stories per month .

Additional comments section 3:


4. Socio-Economic Issues

Patterns of occupancy: Typically one family occupies one housing unit. However, poor families may shelter 1 or 2 families more called “allegados”.

Number of inhabitants in a typical building of this construction type during the day: 10-20

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

Additional comments on number of inhabitants: At present, the average size of a family is 5.5 persons, so if one unit is occupied by up to 3 families, the number of inhabitants in a building may be quite high.

Economic level of inhabitants: Very low-income class (very poor)Low-income class (poor)Middle-income class

Additional comments on economic level of inhabitants: House Price/Annual Income (Ratio) expressed in US$ : 10000/2000 Very Poor 10000/4000 Poor 20000/6150 Middle ClassThe prices correspond to year 2001 and are expressed in US$.The poorest quintile has an average annual income of US$ 2.010. They pay for a 45 m2 dwelling that is subsidized by the State between US$ 5.445 to US$10.885.The next quintile has an average annual income of US$ 4.020, but they live in the same dwellings of the poorest group.The third quintile has an average annual income of US$ 6.150, and they may choose larger or better quality housing. Common prices are between US$ 10.885 to US$27.000. Subsides may be between 15 to 25% of the total cost. In 2013, the average annual income per quintile was the following:first quintile U$ 5600second quintile U$ 9600third quintile U$ 14400and the cost of propriety probably have increased in 50%

Typical Source of Financing: Owner financedPersonal savingsInformal network: friends or relativesSmall lending institutions/microfinance institutionsCommercial banks/mortgagesOther

Additional comments on financing: Other: Governmental subsidies.

Type of Ownership: RentOwn outrightOwn with debt (mortgage or other)

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 as supplement of other insurance (fire, robbery) and people living in these buildings do not have money to pay for that. This insurance typically covers repairs to same condition as before the earthquake.

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:


5. Earthquakes

Past Earthquakes in the country which affected buildings of this type

Year Earthquake Epicenter Richter Magnitude Maximum Intensity
1985 Llolleo, V Region 7.8 VIII (MMI)
1997 Punitaqui, IV Region 6.8 VI-VII (MMI)
2005 Tarapaca, I Region 7.8 9.5 (MSK)
2010 Maule, VII Region 8.8 VIII (MSK)
2014 Iquique, I Region 8.2 VIII (MMI)

Past Earthquakes

Damage patterns observed in past earthquakes for this construction type: After the 1985 earthquake the Ministry of Housing appointed an especial committee to review the seismic effects on social dwellings. About 12.000 units were reinforced masonry type and 44% of them had some type of damage. A 100% of the 3 or more story buildings (2800 units) were severely damaged. The following characteristic damage patterns were observed:- shear cracks in walls, spandrels part of the walls and window piers- vertical cracks at the wall bottom due to compression failure- horizontal cracks at the joints between masonry walls and reinforced concrete floors or foundation- cracks in window piers and walls due to out-of-the-plane action.Some damage occurred in houses located in Illapel during 1997 earthquake due to differential settlement in a slopped terrain.Heavy damage occurred in reinforced masonry houses located in Pozo Almonte during 2005 earthquake, probably because the wall density in one direction was quite low and the construction quality was very poor (Astroza et al, 2005). During 2010 earthquake, a substandard quality of masonry construction was observed in some severely damaged buildings in Rancagua, although the seismic intensity in that location was moderate (Nunez, 2010).

Additional comments on earthquake damage patterns: Up to 1986 there was not any seismic design code for this structural type, so its behavior during March 3, 1985 earthquake was quite bad, mainly due to construction problems, partial grouting in the hollow with reinforcement, bad quality of the mortar and lack of horizontal reinforcement. The same had occurred in the later earthquakes, when requirements according to NCh1928.of1993 have not been accomplished to the full.


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. TRUE
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. TRUE
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. FALSE
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); TRUE
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. FALSE
Wall Openings TRUE
Quality of Building Materials Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). TRUE
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

Additional comments on structural and architectural features for seismic resistance: Average story height is 2.3 m and the thickness brick most used is 14 cm, so the ratio heigth to thickness is less than 30.

Vertical irregularities typically found in this construction type: No irregularities

Horizontal irregularities typically found in this construction type: No irregularities

Seismic deficiency in walls: Low shear strength, so it is difficult to get flexural ductile failure. It is difficult to achieve good anchoring and bonding conditions especially if poor quality masonry units and poor mortar instead of grout are used. Hollow sizes in clay units are inappropriate. Vertical reinforcements without grouting are ineffective. Lack of reinforced concrete horizontal tie-beams may cause out-of-plane bending effects. Lack of appropriate reinforcement at opening edges.Earthquake Damage Patterns: - Shear cracks in walls, spandrel part of the walls and window piers - Vertical cracks at the wall bottom due to compression failure- Horizontal cracks at the joints between masonry walls and reinforced concretefloors or foundation - Cracks in window piers and walls due to out-of-the-planeaction.

Earthquake-resilient features in walls: Relatively high wall density per unit floor. In general these buildings are quite stiff, they must resist a base shear of 10-22% depending on the seismic zone and the story drift must be equal or less than 0.002, (calculated with a reduced spectra, R = 3 or 4).

Seismic deficiency in frames:

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors:

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:


Seismic Vulnerability Rating

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

High vulnerabilty Medium vulnerability Low vulnerability
A B C D E F
Seismic vulnerability class |- o -|

Additional comments section 5


6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening
Lack of appropiate reinforcement Addition of new tie-columns

Additional comments on seismic strengthening provisions: The strengthening procedure consist in confining the masonry wall with reinforced concrete tie-column and tie-beam. This may cost up to 20% of the original cost. With this procedure ductility is also improved.When only some bricks have been damaged, they have been replaced; the same occurs when cracks appeared in the mortar joints.

Has seismic strengthening described in the above table been performed?: The seismic strengthening described in the above table was performed after 1985 earthquake in some “conjuntos”.After 2010 earthquake, most of severe damage buildings were demolished.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?: As it was pointed out in Section 6, after the 1985 earthquake a committee chaired by Prof. Rodrigo Flores was appointed by the Ministry of Housing in order to review the damaged buildings, to prepare restoration projects and supervise its execution.

Was the construction inspected in the same manner as new construction?: Yes

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?: Contractors hired by the government. Engineers were involved.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?: Repaired buildings after 1985 earthquake, had an adequate behavior during 2010 earthquake.

Additional comments section 6:


7. References

  • Construcciones de AlbaM. Astroza and F. DelfCap 5 del libro “El sismo de Marzo de 1985, Chile,” (Ed) J. Monge 1985
  • Bravo L., Martinez C. (1993) “Chile, 50 anos de vivienda social”, Universidad de Valparaiso
  • Giadalah, J. (2000), “Caracteristicas fisicas de los sistemas estructurales utilizados en viviendas sociales en Chile”, Civil Engineer Thesis, Universidad de Chile
  • Hidalgo P., (1993) “Edificios de Albanileria Armada” del libro “Ingenieria Sismica: El caso del sismo del 3 de marzo de 1985”. Ed. Por R. Flores, Editorial Hachette.
  • ICH (1987) “Construccion de Albanilerias Armadas”, Serie Cartilla de Recomendaciones Basicas.No6INN NCh1928.of93 (1993), “Albanileria Armada, Disposiciones para el diseno y calculo”
  • Astroza M.., (2000), Apuntes de Curso: CI 52-H. Diseno de Albanileria Estructural.Division Estructuras y Construccion, Departamento de Ingenieria Civil, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile.
  • Astroza M., M.O. Moroni, Norambuena A., Astroza R. (2005) Intensities and Damage Distribution in the June 2005 Tarapaca, Chile, Earthquake. EERI Special Earthquake Report
  • Astroza M., Moroni M.O., Jaramillo C., (2012) Efectos en los edificios de albanileria. Cap. 9 del libro Mw = 8.8 Terremoto en Chile, Chile, ed. M.O. Moroni
  • Astroza M., Moroni O., Brzev S., Tanner J., (2012) Seismic performance of engineered masonry buildings in the 2010 Maule earthquake. Eartquake Spectra, Vol 28 No S1, pages S385-S406.
  • Jaramillo C. (2011) “Estudio de los efectos del terremoto del 27 de febrero de 2010 en las viviendas de la sexta region” Civil Engineer Thesis, Universidad de Chile
  • Castro F. (2011) “Estudio de los efectos del terremoto del 27 de febrero del 2010 en las viviendas sociales de Constitucion”, Civil Engineer Thesis, Universidad de Chile
  • Nunez M. (2010) Analisis de los danos provocados por el terremoto del 27 de febrero de 2010 a los edificios de Villa Cordillera, Comuna de Rancagua, Civil Engineer Thesis, Universidad de Chile

Authors

Name Title Affiliation Location Email
Ofelia Moroni Civil Engineer/Associate Professor University of Chile Casilla 228/3, Santiago Chile mmoroni@cec.uchile.cl
Cristian Gomez Civil Engineer/Research Assistant University of Chile Casilla 228/3, Santiago Chile crgomez@cec.uchile.cl
Maximiliano Astroza Civil Engineer/Research Assistant University of Chile Casilla 228/3, Santiago Chile mastroza@cec.uchile.cl

Reviewers

Name Title Affiliation Location Email
Sergio Alcocer Director of Research Circuito Escolar Cuidad Universitaria, Institute of Engineering, UNAM Mexico DF 4510, MEXICO salcocerm@iingen.unam.mx
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