World Housing Encyclopedia Report

Country: Yugoslavia

Housing Type: Confined masonry building with concrete floor slabs

Contributors:Nikola MuravljovRadovan Dimitrijevic

Primary Reviewer:Svetlana Brzev

Created on: 6/5/2002Last Modified: 7/2/2003

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........................................................................................ 2Socio-Economic Issues...................................................................................... 3Structural Features............................................................................................. 5Evaluation of Seismic Performance and Seismic Vulnerability.......................... 9Earthquake Damage Patterns............................................................................ 11Building Materials and Construction Process..................................................... 12Construction Economics.....................................................................................14Insurance............................................................................................................15Seismic Strengthening Technologies................................................................. 16References......................................................................................................... 17Contributors........................................................................................................ 18Figures................................................................................................................19

1 General Information

1.1 CountryYugoslavia

1.3 Housing TypeConfined masonry building with concrete floorslabs

1.4 SummaryThis type of construction has been used forsingle-family and medium-rise residentialbuildings throughout urban and rural Yugoslaviaduring the past 30 years. The structure consistsof load-bearing masonry (brick, stone, concreteblock) walls confined with reinforced concreteposts and tie-beams. The walls are typicallymade of hollow clay tiles. Floor slabs arecomposed of prefabricated joists infilled withbrick elements and topped with a reinforcedconcrete slab in-situ.

FIGURE 1A: Typical Building

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 UsedMasonry (brick, concrete block, or stone) construction is widespread both in urban and rural areas ofYugoslavia.

1.7 Urban vs. Rural ConstructionWhere is this construction commonly found?In urban areasIn rural areasIn suburban areasBoth in rural and urban areas X

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2 Architectural Features

2.1 OpeningsAccording to the Yugoslav National Building Code, size of the openings should not exceed 2.5 to 3.5meters (depending on the seismic zone). The size can be increased up to 30% if the openings areconfined with reinforced concrete posts and tie beams.

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) XIs 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 ConfigurationUsually regular shape.

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

Additional Comments: Buildings of this type are single family houses frequent, but there are a lot ofmultiple housing units and mixed too.

2.5 Means of EscapeThere is no additional door besides the main entry in residential buildings of this type. However,standards for commercial buildings define number and type of exit stairs.

2.6 Modification of BuildingsThe most common pattern of modification in residential houses is complete removal or displacement ofinterior walls and columns. House owners usually perform modifications without seeking an advice of acompetent technician (engineer/architect).

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3 Socio-Economic Issues

3.1 Patterns of OccupancyUsually one family occupies one housing unit.

3.2 Number of Housing Units in a Building20 units in each building.

Additional Comments: It varies from one unit per building (single-family house) to 50 units incondominiums.

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

< 55 to 10 X X10-20 X X> 20 X XOther

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

Additional Comments: In case of units with over two bedrooms there is one bathroom and a separate WC.The majority of units are two- or three- bedroom units; mostly there is one bathroom, or one bathroomwith separate WC.

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor /Poor X 50/1Middle Class X 30/1Rich /

Additional Comments: In the last 10 years, the economic situation in Yugoslavia has been very bad. Theaverage net salary is less than 50 $ US per month.

3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner Financed XPersonal SavingsInformal Network: friends and relativesSmall lending institutions/microfinance institutionsCommercial banks / mortages XInvestment poolsCombination (explain)Government-owned housing XOther

3.7 Ownership

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

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4 Structural Features

4.1 Lateral Load-Resisting SystemThe main lateral load-resisting system for this housing type is a wall structure in with brick walls laid inboth directions (transverse and longitudinal) carry lateral seismic forces and transfer them to thefoundations.Reinforced concrete posts and tie-beams are effective in increasing the stiffness and ductility in thisconstruction type and providing an improved level of seismic safety for this type of construction. Details ofconcrete posts and tie-beams are shown in Figure 4A. A possible failure mechanism for confinedmasonry walls is illustrated in Figure 5.

4.2 Gravity Load-Bearing StructureMasonry walls transfer all gravity loads from the roof and floor slabs to the foundations. Minimumthickness for bearing masonry walls is 190 mm (as prescribed by the code).The Yugoslav National Building Code classifies masonry buildings into three categories, depending onthe wall layout:- buildings with walls in transverse direction;- buildings with walls in longitudinal direction, and- buildings with walls in both directions.

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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)13 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: Foundation details are illustrated in Figure 4B.

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

Masonry VaultedComposite masonry and concrete joist X X

StructuralConcrete

Solid slabs (cast in place or precast) X XCast in place waffle slabs X XCast 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

Other

Additional Comments: According to the National Building code, floor/roof must act as rigid diaphragm

4.6 Typical Plan DimensionsLength: 10 - 10 metersWidth: 10 - 10 metersAdditional Comments: Plan dimensions (i.e. length and width) of this building type should not exceed 40to 50 meters. Length to width ratio is usually on the order of 3-4. In case the plan dimensions exceedthese values, the walls need to be divided into sections by means of control joints.

4.7 Typical Number of Stories2 - 4

4.8 Typical Story Height2.8 meters

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Additional Comments: Typical floor height for residential buildings is 2.8 m, and 3.0 m for public buildings.Total height for buildings of this type should not exceed 20 meters (according to the code).

4.9 Typical Span5 meters

Additional Comments: Typical span (between the adjacent concrete posts) ranges from 3 to 6 m. TheNational Building Code prescribes the maximum span of 5 meters.

4.10 Typical Wall DensityVaries from 6% to 12%.

4.11 General Applicability of Answers to Questions in Section 4This description does not relate to one specific building - it outlines generic features of confined masonryconstruction.4

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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

5.2 Seismic FeaturesStructural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall Low shear strength and diagonal

tension cracking as a result of brittleseismic response of unreinforcedmasonry walls subjected to seismicshear forces and gravity loads; brittlebehavior

Typical brick strength is more than 20MPa.

Diagonal tension cracks

Roof and floors In some cases inadequate rigidity ofroof and floor slabs

Concrete post-to-tiebeam joints

Special construction requirements forthe joints are not followed in someinstances.

Reinforced concrete posts and beamsincrease stiffness and ductility in thisconstruction type

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5.3 Seismic Vulnerability RatingVulnerability

High (Very PoorSeismicPerformance)

Medium Low (ExcellentSeismicPerformace)

A B C D E FSeismic

Vulnerability Class0

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)1987 Kraljevo 4.91980 Banja Luka 6.21980 Kopaonik 5.71969 Banja Luka 6.4

Additional Comments: Other earthquakes: 1998 Mionica (magnitude 5.7); 1999 Trstenik (magnitude 5.1).Damage to confined masonry buildings in these earthquakes was not extensive. Figure 6 shows damageto masonry buildings in the 1998 Mionica earthquake (magnitude 5.7). A number of older unreinforcedmasonry buildings were damaged in the earthquake however confined masonry buildings performed welland did not suffer any significant damage, as illustrated in the figure.

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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 Bricks/hollow clay

tiles mortarCharacteristic compressivestrength Bricks : from 7.5-20MPa Hollow clay tiles: from5.0 to 20.0 MPa Mortar: from5-15 MPa)

According to theYugoslav standardsconcretecompressivestrength isdetermined using200 mm cubespecimens. Typicalmasonry units areshown in Figure4D.

Foundations -Concrete -Steelreinforcement

Concrete: minimumcompressive strength 15 MPaSteel: minimum yield stress240 MPa

Minimum 3 fractions of graveland 200 kg/m³ of cement

Foundation detailsare illustrated inFigure 4B.

Roof and floors -Concrete -Steelreinforcement

Concrete strength 15-30 MPasteel yield stress min. 240MPa

Minimum 3 fractions of graveland 300 kg/m³ of cement

Details ofprefabricatedfloor-slabconstruction areshown in Figure4C.

Concrete posts andtie-beams

-Concrete -Steelreinforcement

Concrete minimum strength20 MPa Steel: minimum yieldstress 240 MPa

Minimum 3 fractions of graveland 250 kg/m³ of cement

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?Typically, builders (developers) build the housing of this type. In some cases, builders live in the housesof this type, too.

7.3 Construction ProcessIn this construction system, brick elements must be built and tied together in a specific way. Thickness ofreinforced concrete vertical posts must be equal to the wall thickness. Minimum reinforcement to beprovided in vertical posts consists of 4 -14 mm diameter steel bars tied with 6 mm diameter stirrupsspaced at 250 mm on centre. Tie beams are constructed after the bricklaying is completed. Minimumreinforcement required in the tie beams consists of 4 - 12 mm diameter bars tied with 6 mm stirrups at250 mm on centre spacing. In seismic areas lime/cement mortar has to be used.

7.4 Design/Construction ExpertiseArchitects and engineers design buildings of this type. If certified engineers are not involved in thebuilding design (i.e. non-engineered construction), National Building Code allows the construction of abuilding up to max. two-storey high.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

Title of the code or standard: Technical regulations for masonry construction.Year the first code/standard addressing this type of construction issued: 1987National building code, material codes and seismic codes/standards: Technical regulations forconstruction in seismically prone areas

7.6 Role of Engineers and ArchitectsEngineers and architects work jointly on developing project for buildings of this construction type.

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7.7 Building Permits and Development Control RulesYes No

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

7.8 Phasing of ConstructionYes No

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

Additional Comments: In some cases there are changes and differences between the designed and theconstructed building. In such case, National Building Code prescribes the development of technicaldocumentation describing the "as constructed" condition. Modifications (especially vertical expansion) forthe buildings of this type are common, especially in case of single-family houses.

7.9 Building MaintenanceWho typically maintains buildings of this type?BuilderOwner(s) XRenter(s)No oneOther

Additional Comments: In the urban areas, public companies take care of maintenance for the housingstock.

7.10 Process for Building Code EnforcementFor all newly constructed buildings, building permits confirming that the construction has been done inconformance with the National Building Code must be issued; the code also prescribes the seismic zonethe buildings are located in.Yugoslavia (and Serbia) are the part of the Balkan Peninsula, which is known to be one of the mostseismically prone regions of Europe. However, until the catastrophic 1963 Skopje (Macedonia)earthquake, there were no seismic codes or regulations in the country. In 1964, the Preliminary NationalBuilding Code (including the seismic provisions) was issued. The latest edition of the National BuildingCode was issued in 1987. In addition to the National Code, Euro Codes have been used in the country aswell.

7.11 Typical Problems Associated with this Type of ConstructionA comprehensive construction quality control system, including building inspection and material testing,does not exist for this construction type.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)Construction cost is about 100 to 150 $US/m² of built-up area (structure only), whereas the price of thefinished building is on the order of 200 to 300 $US/m² of built-up area.

8.2 Labor Requirements (estimate)Construction of a typical building of this type (built-up area of 120-200 m²) takes approximately 6 months,depending on the finances. It should be also noted that this type of construction requires a limited numberof trained labor and technical personnel. Majority of the other construction labor involved in this type ofconstruction are generally unskilled.

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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

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?The annual insurance rate is 0.45% of the building value increased by 15% to account for earthquakerisk.

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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)

Low shear strength and diagonaltension cracking as a result of brittleseismic response of unreinforcedmasonry walls subjected to shear forcesand gravity loads; brittle behavior

Reconstruction of damaged walls; New reinforced concrete walloverlay; Injection grouting of cracks; Application of carbon fiberlaminates bonded diagonally to the walls

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Yes, all strengthening methods were used in design practice. Structural engineers provide designspecifications for the seismic strengthening design.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?In most of the cases, seismic strengthening has been performed as a part of post-earthquakerehabilitation (e.g. after the 1979 Montenegro earthquake or 1998Mionica earthquake).

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?Usually it was owner/user who performed the construction, with competent participation of an architectand engineer.

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?The buildings that were seismically upgraded were generally not subjected to another major earthquake.However, it is expected that the strengthened buildings would show improved seismic performance ifsubjected to an earthquake.

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11 ReferencesCollection of Yugoslav Codes and Standards (1995). Lateral Forces, Masonry, Belgrade, Yugoslavia.

B. Petrovic: "Selected Chapters of Earthquake-Resistant Construction"- Structural Book, Belgrade,Yugodslavia, 1985.

B. Acimovic: "The Earthquake Influence on Buildings in the Region of Mionica" - Proceedings, Institute forTesting Materials IMS, Belgrade, Yugoslavia, 1998.

M. Muravljov, B. Stevanovic: "Masonry and Wooden Construction", Faculty for Structural Engineering,Belgrade, Yugoslavia, 1999.

M. Muravljov, N. Muravljov, D. Denic:" Effects of Concrete Posts in Block and Brick Walls", Congress SIG,Vrnjacka Banja, 1999.

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12 ContributorsName Nikola Muravljov Radovan DimitrijevicTitle Senior Structural Engineer Consultant AdvisorAffiliation Structural Engineering Department Duros CompanyAddress IMS Institute, Belgrade, Bul. Vojvode

Misica 43Ace Joksimovica 102, Zarkovo

City Belgrade BelgradeZipcode 11 000 11 000Country Yugoslavia YugoslaviaPhone (381 11) 653-015 (381 11) 501 248Fax (381 11) 651-033 (381 11) 501 248Email koljaka@Eunet.yu Rakadim@Eunet.yuWebpage

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13 Figures

FIGURE 1A: Typical Building

FIGURE 1B: Typical building

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FIGURE 1C: Typical building

FIGURE 1D: Typical building

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FIGURE 1E: Typical building

FIGURE 1F: Typical building

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FIGURE 2: Key Load-Bearing Elements

FIGURE 3: Plan of a Typical Building

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FIGURE 4A: Details of concrete posts and tie beams)

FIGURE 4B: Foundation Details

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FIGURE 4C: Floor slab details (an example of a precast floor slab type LMT)

FIGURE 4D: Typical masonry units used in wall and floor-slab constructione

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FIGURE 5: A possible failure mechanism for confirned masonry walls

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FIGURE 6: Damage to masonry buildings in the 1998 Mionica earthquake.

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