World Housing Encyclopedia Report

Country: Chile

Housing Type: Buildings with hybrid masonry walls.

Contributors:Ofelia MoroniCristian GómezMaximiliano Astroza

Primary Reviewer:Sergio Alcocer

Created on: 6/5/2002Last Modified: 6/17/2003

This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions, and recommendations expressed herein are those

of the various participants, and do not necessarily reflect the views of the Earthquake EngineeringResearch Institute, the International Association for Earthquake Engineering, the Engineering Information

Foundation, John A. Martin & Associates, Inc. or the participants' organizations.

Table of Contents

General Information............................................................................................1Architectural Features........................................................................................ 3Socio-Economic Issues...................................................................................... 4Structural Features............................................................................................. 6Evaluation of Seismic Performance and Seismic Vulnerability.......................... 10Earthquake Damage Patterns............................................................................ 13Building Materials and Construction Process..................................................... 14Construction Economics.....................................................................................16Insurance............................................................................................................17Seismic Strengthening Technologies................................................................. 18References......................................................................................................... 19Contributors........................................................................................................ 20Figures................................................................................................................21

1 General Information

1.1 CountryChile

1.3 Housing TypeBuildings with hybrid masonry walls.

1.4 SummaryThis housing type represents a commonmulti-family urban construction in Chile. Thisconstruction practice started in the 1980s, and itis mainly used for dwellings and up to 4-storyapartment buildings. The main load-bearingsystem consists of masonry walls in transversedirection and reinforced concrete walls in thelongitudinal direction. In some cases,longitudinal walls are of reinforced masonryconstruction (instead of concrete construction).Masonry walls in the transverse direction areusually confined with concrete posts at the ends(like in confined masonry construction).Buildings of this type are usually regular in planand in elevation. Seismic design code does notaddress buildings of this type, however theChilean Ministry of Housing has issuedspecifications for 1 and 2-story dwellings, whichhave been mainly followed in the design (even incase of taller buildings of this type).Performance of buildings of this type in the 1985Llolleo earthquake was rather poor, with mostbuildings experiencing structural damage.

FIGURE 1A: Typical Building (photo)

1.5 Typical Period of Practice for Buildings of This Construction TypeHow long has thisconstruction been practiced< 25 years< 50 years X< 75 years< 100 years< 200 years> 200 years

Is this construction still being practiced? Yes NoX

1.6 Region(s) Where UsedThis housing type is used throughout Chile.

1.7 Urban vs. Rural ConstructionWhere is this construction commonly found?In urban areas XIn rural areasIn suburban areas

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Both in rural and urban areas

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2 Architectural Features

2.1 OpeningsIn each longitudinal façade may be 3 to 4 openings of 0.8 to 1.5 m width probably equally spaced.The ratio for the overall window and door areas over the wall surface area is about 25 - 30%.

2.2 SitingYes No

Is this type of construction typically found on flat terrain? XIs this type of construction typically found on sloped terrain? (hilly areas)Is it typical for buildings of this type to have common walls with adjacentbuildings?

X

The typical separation distance between buildings is 5 meters

2.3 Building ConfigurationThe typical shape of a building plan is rectangular. These buildings are characterized with the regularstructural layout, symmetrical with regards to at least one axis. As a result, there is a uniform distributionof stiffness both in plan and in elevation.

2.4 Building FunctionWhat is the main function for buildings of this type?Single family houseMultiple housing units XMixed use (commercial ground floor, residential above)Other (explain below)

Additional Comments: Buildings of this type may be single family houses too.

2.5 Means of EscapeIf single-story building, there is an additional door besides the main entry. If more than one floor, there isnot an additional exit stair besides the main stairs.

2.6 Modification of BuildingsTypical patterns of modification observed are infill balconies or hillock on the top floor.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyTypically one family occupies one housing unit. However, poor families may shelter 1 or 2 families morecalled "allegados".

3.2 Number of Housing Units in a Building8 units in each building.

Additional Comments: Buildings may be from 1 to 4 floors. One-floor houses may be isolated or groupingup to 4 units. Two floor houses may be isolated or grouping up to 8 units. Up to 6 units per floor may existin higher buildings.

3.3 Average Number of Inhabitants in a BuildingHow many inhabitants reside in a typical building of thisconstruction type?

During the day / businesshours

During the evening / night

< 5 X5 to 10 X10-20 X> 20 XOther

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

3.4 Number of Bathrooms or Latrines per Housing UnitNumber of Bathrooms: 1Number of Latrines: 0

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor X 8000/2000Poor X 25000/6000Middle Class X 50000/12000Rich /

3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner Financed XPersonal Savings XInformal Network: friends and relatives XSmall lending institutions/microfinance institutions XCommercial banks / mortages XInvestment pools XCombination (explain)Government-owned housingOther

Additional Comments: This type of dwelling for poor and very poor people is subsidized by the State.

3.7 Ownership

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Type of Ownership/OccupancyRent XOwn outright XOwn with Debt (mortgage or other) XUnits owned individually (condominium)Owned by group or poolLong-term leaseOther

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4 Structural Features

4.1 Lateral Load-Resisting SystemThe main lateral load-resisting system in the buildings of this type consists of shear walls tied together atfloor levels by means of reinforced concrete beamsIn the transverse direction, the masonry walls are partially reinforced or confined with reinforced concretecolumns. In the longitudinal direction, there are reinforced masonry or reinforced concrete walls orpartially confined walls (mainly used around the openings). The reinforced masonry walls have a f 10 mmbar at each end plus f 8 mm bars distributed along the wall. Although the maximum allowed spacingbetween bars is 84 cm they are located between 120 and 150 cm. The diameter of the extreme bars isless than required (12 mm diameter) for dwellings higher than 2 story. Horizontal reinforcement does notmeet the minimum steel ratio requirement of 0.06.The brick thickness in the exterior (façade) walls is 140 mm and 150 mm in the interior walls. Although thecores and voids containing reinforcement should be filled with grout, this is not accomplished in all cases.Most of the time the blocks are filled with the same mortar used in the horizontal joints. In addition, thesize of the hollow cores in the ceramic unit is quite small so it is difficult to fill it. Concrete blocks (mostlyused in the north of Chile) have larger hollow cores but they have water leakage problems and since 1997the use of these blocks has been banned in Central Chile.

4.2 Gravity Load-Bearing StructureShear walls in both directions.Reinforced concrete slab. Average thickness 11 cm.

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4.3 Type of Structural SystemMaterial Type of

Load-BearingStructure

# Subtypes

Masonry Stone masonrywalls

1 Rubble stone (field stone) in mud/lime mortar or withoutmortar (usually with timber roof)

2 Massive stone masonry (in lime or cement mortar)Earthen walls 3 Mud walls

4 Mud walls with horizontal wood elements5 Adobe block or brick walls6 Rammed earth/Pise construction

Unreinforced brickmasonry walls

7 Unreinforced brick masonry in mud or lime mortar8 Unreinforced brick masonry in mud or lime mortar with

vertical posts9 Unreinforced brick masonry in cement or lime mortar

(various floor/roof systems)Confined masonry 10 Confined brick/block masonry with concrete posts/tie

columns and beamsX

Concrete blockmasonry walls

11 Unreinforced in lime or cement mortar (various floor/roofsystems)

12 Reinforced in cement mortar (various floor/roof systems) X13 Large concrete block walls with concrete floors and roofs

Concrete Moment resistingframe

14 Designed for gravity loads only (predating seismic codes i.e.no seismic features)

15 Designed with seismic features (various ages)16 Frame with unreinforced masonry infill walls17 Flat slab structure18 Precast frame structure19 Frame with concrete shear walls-dual system20 Precast prestressed frame with shear walls

Shear wall structure 21 Walls cast in-situ22 Precast wall panel structure

Steel Moment resistingframe

23 With brick masonry partitions24 With cast in-situ concrete walls25 With lightweight partitions

Braced frame 26 Concentric27 Eccentric

Timber Load-bearingtimber frame

28 Thatch29 Post and beam frame30 Walls with bamboo/reed mesh and post (wattle and daub)31 Wooden frame (with or without infill)32 Stud wall frame with plywood/gypsum board sheathing33 Wooden panel or log construction

Various Seismic protectionsystems

34 Building protected with base isolation devices or seismicdampers

Other 35

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4.4 Type of FoundationType Description

Shallow Foundation Wall or column embedded in soil, without footingRubble stone (fieldstone) isolated footingRubble stone (fieldstone) strip footingReinforced concrete isolated footingReinforced concrete strip footing XMat foundationNo foundation

Deep Foundation Reinforced concrete bearing pilesReinforced concrete skin friction pilesSteel bearing pilesWood pilesSteel skin friction pilesCast in place concrete piersCaissons

Other

Additional Comments: Usually the foundation does not have reinforcement, unless the soil is clay or silt.Concrete strip footing are used only under the walls plus reinforced tie beams in between.

4.5 Type of Floor/Roof SystemMaterial Description of floor/roof system Floor Roof

Masonry VaultedComposite masonry and concrete joist

StructuralConcrete

Solid slabs (cast in place or precast) XCast in place waffle slabsCast in place flat slabsPrecast joist systemPrecast hollow core slabsPrecast beams with concrete toppingPost-tensioned slabs

Steel Composite steel deck with concrete slabTimber Rammed earth with ballast and concrete or plaster finishing

Wood planks or beams with ballast and concrete or plaster finishingThatched roof supported on wood purlinsWood single roofWood planks or beams that support clay tilesWood planks or beams that support slate, metal asbestos-cement or plasticcorrugated sheets or tilesWood plank, plywood or manufactured wood panels on joists supported bybeams or walls

X

Other

Additional Comments: In the analysis the floor is considered to be a rigid diaphragm.

4.6 Typical Plan DimensionsLength: 6 - 12 metersWidth: 6 - 12 metersAdditional Comments: Unit average areas are 35-40 m².

4.7 Typical Number of Stories4

4.8 Typical Story Height2.3 meters

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4.9 Typical Span6 meters

4.10 Typical Wall Density1.5 to 7.0 % in each direction. The average is about 3.2% in each direction. The wall density per unit floorhas been related to expected level of damage; for values lower than 1.15% some moderate damage maybe expected. Generally, lower values correspond to 3 or 4 story buildings. The wall density and walldensity per unit floor variation with time are shown in Figure 5A, 5B and 5C.

4.11 General Applicability of Answers to Questions in Section 4A data base with 250 groups of masonry dwellings has been prepared. About 44% of it belongs to thishousing type.

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5 Evaluation of Seismic Performance and Seismic Vulnerability

5.1 Structural and Architectural Features: Seismic ResistanceStructural/ArchitecturalFeature

Statement True False N/A

Lateral load path The structure contains a complete load path for seismic force effects fromany horizontal direction that serves to transfer inertial forces form thebuilding to the foundation.

X

Buildingconfiguration

The building is regular with regards to both the plan and the elevation. X

Roof construction The roof diaphragm is considered to be rigid and it is expected that the roofstructure will maintain its integrity, i.e.. shape and form, during anearthquake of intensity expected in this area.

X

Floor construction The floor diaphragm(s) are considered to be rigid and it is expected that thefloor structure(s) will maintain its integrity, during an earthquake of intensityexpected in this area.

X

Foundationperformance

There is no evidence of excessive foundation movement (e.g. settlement)that would affect the integrity or performance of the structure in anearthquake.

X

Wall and framestructures-redundancy

The number of lines of walls or frames in each principal direction is greaterthan or equal to 2.

X

Wall proportions Height-to-thickness ratio of the shear walls at each floor level is: 1) Lessthan 25 (concrete walls); 2)Less than 30 (reinforced masonry walls); 3)Less than 13 (unreinforced masonry walls).

X

Foundation- wallconnection

Vertical load-bearing elements (columns, walls) are attached to thefoundations; concrete columns and walls are doweled into the foundation.

X

Wall-roofconnections

Exterior walls are anchored for out-of-plane seismic effects at eachdiaphragm level with metal anchors or straps.

X

Wall openings The total width of door and window openings in a wall is: 1) for brickmasonry construction in cement mortar: less than 1/2 of the distancebetween the adjacent cross walls; 2) for adobe masonry, stone masonryand brick masonry in mud mortar: less than 1/3 of the distance between theadjacent cross walls; 3) for precast concrete wall structures: less than 3/4 ofthe length of a perimeter wall.

X

Quality of buildingmaterials

Quality of building materials is considered to be adequate per requirementsof national codes and standards (an estimate).

X

Quality ofworkmanship

Quality of workmanship (based on visual inspection of few typical buildings)is considered to be good (per local construction standards).

X

Maintenance Buildings of this type are generally well maintained and there are no visiblesigns of deterioration of building elements (concrete, steel, timber).

X

Other

Additional Comments: Usually the roof is made of wood planks or beams that support slate, metal,asbestos-cement or plastic corrugated sheets or tiles

5.2 Seismic FeaturesStructural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall Unknown shear strength, so it is difficult

to get flexural ductile failure. It is difficultto achieve good anchoring and bondingconditions especially if poor qualitymasonry units and poor mortar insteadof grout are used. Hollow sizes in clayunits are inappropriate. Verticalreinforcements without grouting areineffective. Lack of reinforced concretetie-post may cause shear failure andout-of-plane bending effects. The tensilesteel bar in one end does not representa proper tie-post. Lack of appropriatereinforcement at opening edges.

High wall density. Perimeter walls with shear cracks, outof plumb and separations at thecorners. -crushed at the wall bottom dueto compression failure-interior wallsusually confined had only small cracks.

Frame (columns,beams)Roof and floors

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5.3 Seismic Vulnerability RatingVulnerability

High (Very PoorSeismicPerformance)

Medium Low (ExcellentSeismicPerformace)

A B C D E FSeismic

Vulnerability Class< 0 >

0 - probable value< - lower bound> - upper bound

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6 Earthquake Damage Patterns

6.1 Past Earthquakes Reported To Affect This ConstructionYear Earthquake Epicenter Richter magnitude(M) Maximum Intensity (Indicate

Scale e.g. MMI, MSK)1997 Punitaqui 6.8 VI-VII1985 Llolleo 7.8 VIII1971 La Ligua 7.5 IX

Additional Comments: Due to 1971 earthquake, about 1000 one-story houses at Choapa Valley partiallycollapsed. The masonry walls had tie-reinforced concrete beam and some tensile bars at the extremes ofthe walls or at the corners of joint between walls. After the 1985 earthquake the Ministry of Housingappointed an especial committee to review the seismic effects on social dwellings. About 84,000 unitswere reviewed, concluding that 50% of the units had some structural damage, being 2.6% of it hybridreinforced masonry 3 or 4 story buildings and all of them had some type of damage. The followingcharacteristic damage patterns were observed: # perimeter walls with shear cracks, out of plumb andseparations at the corners. # crushed at the wall bottom due to compression failure # interior walls usuallyconfined had only small cracks. Some damage occurred in houses located in Illapel during 1997earthquake due to differential settlement on a slopped terrain.

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7 Building Materials and Construction Process

7.1 Description of Building MaterialsStructural Element Building Material Characteristic Strength Mix Proportions/ Dimensions CommentsWalls Clay brick Artisan

brick6-12 2-8 14 x 29 20 x 30 10-20 15-40

Foundations Concrete block 3-10 /39x19x9 / 39x14x9/ 5-12Other: Beams Concrete Steel

A44-28H18 - 20(3)

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?Construction companies hired by the state build it.

7.3 Construction ProcessOne contractor builds large quantities of this type of buildings, so project management and controltechniques are used in order to increase productivity and to diminish cost. However, inspection andsupervision is difficult because too many activities are done simultaneously.When constructing the vertical reinforcing bars are usually first placed into position before laying themasonry units. Then, the horizontal bars can be placed in horizontal mortar joints. Finally, verticalreinforcement is grouted as the work progresses. For confined walls the brick are laid in first place andthen the columns and beams are concrete against the walls. ICH is developing guidelines to build thistype of structures properly.With respect to equipment the following is commonly used: concrete mix, trucks, traveling crane, winch.

7.4 Design/Construction ExpertiseThe structural engineer will have 6 years of studies and more than 3-5 years of experience. Theconstruction engineer may have 6 years of studies and less experience than the structural engineer. Forprivate projects there is not compulsory inspection during the construction and no peer revision of thestructural project, but when inspection does exist larger masonry compression strength are allowed. Thedesigner may visit the construction site once or twice during the construction. Projects hired by the stateare revised and inspected during construction by SERVIU.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

National building code, material codes and seismic codes/standards: The seismic loads are determinedbased on the NCh433.of96 "Seismic Design for Buildings". In general, these buildings are quite stiff andthey must resist a base shear of 10-22% depending on the seismic zone; the story drift must be equal orless than 0.002. A specific code addressing this type of construction does not exist. Designers followsome requirements of NCh1928.Of93 (Reinforced Masonry Design Code) or NCh 2123.Of97 (ConfinedMasonry Design Code) which are too strict. In general, designers follow guidelines prepared by theMinistry of housing for 1 or 2 stories houses, independently of the number of floors of the project.

7.6 Role of Engineers and ArchitectsSee the answer to 7.3

7.7 Building Permits and Development Control RulesYes No

Building permits are required XInformal construction XConstruction authorized per development control rules X

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7.8 Phasing of ConstructionYes No

Construction takes place over time (incrementally) XBuilding originally designed for its final constructed size X

7.9 Building MaintenanceWho typically maintains buildings of this type?BuilderOwner(s) XRenter(s) XNo one XOther X

Additional Comments: As it was pointed out in 6.0 after the 1985 earthquake a committee was appointedby the Ministry of Housing, in order to review the damaged buildings, to prepare restoration projects andsupervise its execution.

7.10 Process for Building Code EnforcementThe building design must follow the NCh433.of96 code. SERVIU a governmental office in charge of socialdwellings has a professional staff to review the projects and to inspect during construction. In case ofdamage an arbitrage process may take place at the court of justice.

7.11 Typical Problems Associated with this Type of ConstructionPartial grouting in vertical reinforcement. Bending of reinforcement barsBad reinforcement detailing at the corners or intersection of walls.Insufficient concrete covers for horizontal reinforcement.Inadequate construction joint, stone cage in reinforced concrete element.Lack of quality of brick materials, lack of control of humidity, so the serviceability of the buildings is indiscussion.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)The total cost of this type of building can be blotted out in main structure 62%, finishing work 25%,urbanization, operating cost and profit 13%.The cost of one unit is 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).

8.2 Labor Requirements (estimate)At present, depending on technology used, the construction may take 2 - 3 stories per month of severalunits simultaneously built.

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9 Insurance

9.1 Insurance IssuesYes No

Earthquake insurance for this construction type is typically available XInsurance premium discounts or higher coverages are available for seismicallystrengthened buildings or new buildings built to incorporate seismically resistantfeatures

X

Additional Comments: 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.

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?Repaired cost to leave the building in the same condition as previous the earthquake.

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10 Seismic Strengthening Technologies

10.1 Description of Seismic Strengthening ProvisionsType of intervention Structural Deficiency Description of seismic strengthening provision usedRetrofit(Strengthening)

Lack of appropriate confinement The strengthening procedure consist in confining the masonry wallwith reinforced concrete tie-column and tie-beam. This may cost up to20% of the original cost. With this procedure ductility is also improved.

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Only after March 3, 1985 earthquake.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?As a repair following earthquake damage.

10.4 Was the construction inspected in the same manner as new construction?Yes.

10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?A contractor hired by the Ministry of Housing.

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?None subsequent earthquakes has hit that zone.

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11 ReferencesAstroza M.., (2000), Apuntes de Curso: CI 52-H. Diseño de Albañilería Estructural.División Estructuras yConstrucción, Departamento de Ingeniería Civil, Facultad de Ciencias Físicas y Matemáticas,Universidad de Chile.

Bravo L., Martinez C. (1993) "Chile, 50 años de vivienda social", Universidad de Valparaíso

Escobar, P. (1986) "Influencia del suelo de fundación del gran Santiago en el comportamiento sísmico",Civil Engineer Thesis, Universidad de Chile.

Bravo L., Martinez C. (1993) "Chile, 50 años de vivienda social", Universidad de Valparaíso

Catastro de viviendas con daños para el terremoto de Punitaqui 1997, IV región, Base de datos de laIntendencia de la IV Región.

Giadalah, J. (2000), "Características físicas de los sistemas estructurales utilizados en viviendas socialesen Chile", Civil Engineer Thesis, Universidad de Chile

Gomez, C. (2001) "Caracterización de sistemas estructurales usados en las viviendas de hormigónarmado y albañilería reforzada en Chile" Civil Engineer Thesis, Universidad de Chile.

ICH (1992) "Construcción de Albañilerías Armadas", Instituto del Cemento y Hormigón

INE, (1980-1986), (1994-1998), "Anuario de Edificación", Instituto Nacional de Estadística.

INN NCh1928.of93 (1993), "Albañilería Armada, Disposiciones para el diseño y cálculo"

INN NCh2123.Of97 (1997), "Cálculo y Diseño de Edificios de Albañilería Confinada"

Palma V., (1998) "Alternativas de estructuración y diseño de viviendas sociales", Civil Engineer Thesis,Universidad de Chile

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12 ContributorsName Ofelia Moroni Cristian Gómez Maximiliano AstrozaTitle Civil Engineer / Assistant

ProfessorCivil Engineer / ResearchAssistant

Civil Engineer/ AssociateProfessor

Affiliation University of Chile University of Chile University of ChileAddress Casilla 228/3 Casilla 228/3 Casilla 228/3City SantiagoZipcodeCountry Chile Chile ChilePhone 562-6784372 562-7441153 562-6784372Fax 562-6892833 562-6892833 562-6892833Email mmoroni@cec.uchile.cl crgomez@cec.uchile.cl mastroza@cec.uchile.clWebpage

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13 Figures

FIGURE 1A: Typical Building (photo)

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FIGURE 1B: A Typical Housing Complex

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FIGURE 2: Key Load bearing Elements

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FIGURE 3A: Plan of a Typical Building

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FIGURE 3B: Typical Building Plan

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FIGURE 4A: Critical Structural Details: An Elevation of a confined masonry wall

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FIGURE 4B: Critical Structural Details - An elevation of a confined masonry wall showing reinforcementdetails

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FIGURE 4C: Critical Structural Details - A vertical section through the wall showing reinforced concretebeams at floor levels

FIGURE 4D: Critical Structural Details - An elevation of a confined masonry wall

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FIGURE 5A: Wall density per floor area for different masonry buildings

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FIGURE 5B: Wall Density for Hybrid Masonry Buildings

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FIGURE 5C: Wall Density per Unit Floor- Hybrid Masonry

FIGURE 6A: A Photograph Illustrating Typical Earthquake Damage (1997 Punitaqui earthquake)

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FIGURE 6B: Earthquake Damage (1997 Punitaqui earthquake)

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FIGURE 6C: Earthquake Damage (1997 Punitaqui earthquake)

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