World Housing Encyclopedia Report

Country: Cyprus

Housing Type: Gravity designed reinforced concrete frame buildings with unreinforcedmasonry infill walls.

Contributors:V. Levtchitch

Primary Reviewer:Craig Comartin

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............................................................................................. 5Evaluation of Seismic Performance and Seismic Vulnerability.......................... 9Earthquake Damage Patterns............................................................................ 12Building Materials and Construction Process..................................................... 13Construction Economics.....................................................................................15Insurance............................................................................................................16Seismic Strengthening Technologies................................................................. 17References......................................................................................................... 18Contributors........................................................................................................ 19Figures................................................................................................................20

1 General Information

1.1 CountryCyprus

1.3 Housing TypeGravity designed reinforced concrete framebuildings with unreinforced masonry infill walls.

1.4 SummaryThis type of concrete apartment building waswidely constructed after the1974 Turkishinvasion in order to accommodate approximately200,000 refugees. Typically, these buildings arelow-rise (up to 5 stories) apartment blocks. As arule, architectural considerations prevail overstructural requirements. Very often columns arelocated irregularly and do not form a definitegrid. Soft ground stories are used for car-parks(garages) and shops. Staircases and lift(elevator) shafts are not located symmetrically.Taking into account the inherent seismicdeficiencies of this structural type, designmistakes, construction faults, unavoidable aging,lack of maintenance, accumulation of minordamage due to previous earthquakes andoccasional overloading, the deterioration ofconcrete and the corrosion of the reinforcing bar,the vulnerability of these buildings should bevery high. But against all odds the majority ofthese buildings have stood well in numeroussmall earthquakes and exhibited rather goodperformance under the peak groundaccelerations of up to 0,15g (the maximumexpected in Cyprus). Damage and destructionhave been very selective depending on the localsoil conditions and periods of natural vibration.

FIGURE 1: 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

Additional Comments: Since 1994 the seismic code for design and construction was introduced.

1.6 Region(s) Where Used

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Throughout the country

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

Additional Comments: This type of housing accounts for more than 30% of the total dwelling stock. Inurban areas these buildings constitute approximately 45% of houses.

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2 Architectural Features

2.1 OpeningsIn external infill-walls openings may cover up to 40% of the wall surface and in internal walls - up to 20%.Openings in infill-walls (if they are not located immediately near the columns) do not constitute a majorvulnerability factor. Framing of continuous lintels into columns is to be considered.

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 Three meters

2.3 Building ConfigurationBasically rectangular, but rather often an irregular location of columns and asymmetric position ofstairs-and-lift-shafts, re-entrant corners and set-backs transform them into structurally irregular systems.Sometimes a building plot shape influences the configuration of buildings.

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) XOther (explain below)

Additional Comments: In the vast majority of cases there is a mixed functional use.

2.5 Means of EscapeIn buildings of more than one floor, commonly there is an additional exit stair for the emergency escape.

2.6 Modification of BuildingsInternal infill walls and partitions can be removed or added to meet new functional requirements. As a rule, columns remain unaffected. Balconies can be supplemented by enclosing walls made of variousmaterials. In one-two storey private buildings there can be the plan extensions of different types withoutpaying any attention to a seismic structural integrity of a modified structure. Practically all privateone-three storey buildings are provided with the starter reinforcement bars projecting from the columns forthe future construction of additional stories. This strong desire for the additions is not always backed bythe initially provided foundations and the structural capacities of a first-phase constructed frame. Theunprotected starter bars are usually extensively corroded and practically cannot serve the purpose.Moreover, their corrosion inevitably propagates inside and there are cracks due to corrosion productsexpansion. Occasionally, the additional stairs have been constructed.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyOne family per housing unit.

3.2 Number of Housing Units in a Building8- 14 units in each building.

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 X10-20> 20 XOther

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

Additional Comments: Usually 1 bathroom per unit, but in more recent buildings can be 2.

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor /Poor X /Middle Class X 4/1Rich /

Additional Comments: Reach-15%, middle class-75%, poor-10%.

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

3.7 OwnershipType of Ownership/OccupancyRent XOwn outrightOwn with Debt (mortgage or other)Units owned individually (condominium) XOwned by group or poolLong-term leaseOther

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4 Structural Features

4.1 Lateral Load-Resisting SystemReinforced concrete frame acts as the stabilizing-lateral load resisting system. The rigid, brittle infill wallshave approximately two times smaller interstory-drift capacities than those of the columns. Their jointresponse can be utilized only within low levels of lateral displacements. After shearing of infill walls, thewhole of the lateral load is suddenly transferred to columns and this makes them very vulnerable.

4.2 Gravity Load-Bearing StructureCommon cast-in-situ R.C. frame, basically of usual dimensions and typical proportions. In spite offrequent irregularities of the beam-arrangement, the commonly used 150 mm deep slab over usual spanscontributes to the lateral diaphragm action of the floor-and-roof system.Re-entrant corners and set-backs were provided without taking into account torsional effects, distributionof lateral seismic forces and overloading of outward external columns. "Strong column-weak beam"principle was not followed. Just the opposite is the case. Rigid and slender columns are used within thesame storey and "short column effect" was not considered. Interaction between flexible R.C. frames andrigid-low-strain-capacity-brittle infill walls was not addressed. Joints between them are not specified.Generally, deformation compatibility was not analyzed. Usually, floor systems are rigid enough in theirown plane to act as the horizontal stiff diaphragm and to distribute seismic forces between columns inaccordance with their rigidities. But rather often some beams are omitted or arranged in one directiononly. The continuity is disrupted, slab supports are altered, membrane action is affected, load path iscomplicated and frame lateral performance is influenced adversely. Besides, sometimes slabs have thehollow core clay bricks as the filler in tensile (bottom) zone. Since seismic forces alternate in both verticaland horizontal directions and generate torsional movements this is not a good choice to resist them.Spans of a single continuous beam usually differ considerably, but their cross-sections remain the sameand, hence, their relative rigidities and forces transferred to them are quite different. End anchorage ofbeams and slabs in the outer bays is not adequate. Top reinforcement in both beams and slabs is notsufficient in terms of quantity and length of extension into spans. Usually there is overcapacity of bottomreinforcement and undercapacity of the top reinforcement.In spite of the fact that these buildings were neither designed nor detailed for earthquakes, they havecertain reserves of lateral resistance. Tied-up columns can take lateral drifts. Floor-and-roof diaphragmsthis. Provided that anchorage and continuity are maintained, concrete structures reinforced with ductilesteel have an inherent ability to adapt to cyclic loadings due to spatial redistribution of stresses, change ofrigidities and natural periods of vibration, strain hardening of steel. In many cases their availablecapacities are somewhat higher than those determined by simplified methods of analysis.

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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 beamsConcrete 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)

X

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 footing XReinforced concrete strip footingMat 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: In the coastal areas the mat foundations were sometimes used.

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) X 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

Other

Additional Comments: In most cases floors and roofs can be treated as the rigid diaphragms.

4.6 Typical Plan DimensionsLength: 12 - 12 metersWidth: 12 - 12 meters

4.7 Typical Number of Stories3 - 5

4.8 Typical Story HeightApproximately 3 meters

4.9 Typical Span3.5 to 4.5 meters

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4.10 Typical Wall DensityApproximately 10% (infill-walls)

4.11 General Applicability of Answers to Questions in Section 4This description is based on many observations and represents the type of structures, not a particularbuilding. It is applicable to all R.C. frame buildings with infill walls, not specifically designed and detailedfor seismic loadings. Buildings with concrete walls were not included in this discussion, because theyhave a very different response. Columns with a large aspect ratio (>2) are used, but as a rule, they arechaotically oriented. Still this provides an additional safety. Rigid cores enclosing staircases can distortthe distribution of stresses.

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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 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 Features

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Structural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall Rigid, brittle infill-walls are in contact

with the much more flexible columns.Infill-walls suffer heavy damagethemselves and trigger the damage anddestruction of columns. A low qualitysite-prepared cement mortar has beenused. The characteristic bond can be aslow as 0.015 MPa, i.e. approximately 10times lower than that required for agood quality masonry. Vertical jointshave not been filled with mortar. Neitheran effect of infill panels on a frame northat of a swaying R.C. frame on a brittleinfill walls have been considered.

In spite of their brittleness masonry infillpanels can absorb and dissipate aconsiderable part of earthquake energy.Their strength must be lower than thatof a basic R.C. frame. After breakingdown of infill panels the consecutiveearthquake motions must be within thecapacities of a R.C. frame alone. Theundesirable interaction betweencolumns and walls may be prevented byproviding of separation joints. An infillpanel can be upgraded to a structuraltype, which will respond jointly with R.C.frames, i.e. as boundary columns with awall or a column with the side-walls.

Extensive diagonal cracking due to theprincipal tensile stresses is estimated totake place at interstory drifts between1/400 and 1/200, while the commonR.C. columns can accommodateinterstory drifts of up to 1/100 or evenmore. Separation gaps at the cornersand along beams are the commonfeature. Occasionally, the out-of- the-plane loss of stability has beenobserved. Sometimes, the lateral shearcracks have been developed.

Frame (columns,beams)

Columns are not specifically designedand detailed for seismic forces. "Strongcolumn-weak beam" principle was notfollowed. Shear and confiningreinforcement is not adequate. Panelzones of beam-column joints are notprovided with lateral reinforcement andfrequently are not compacted properly.Stiff and flexible columns are usedwithin one floor. Soft ground floor.Columns with the large aspect ratio areused. Torsion of peripheral columns isnot addressed. Anchorage of lateralreinforcement inside the core is notprovided. Shear reinforcement of beamsis not sufficient. Confining within thepotential plastic-hinge zones is notadequate. Excessive bottomreinforcement and not adequate topreinforcement. Not sufficient length oftop reinforcement. End anchorage in theouter bays is not sufficient.

Although columns were not designed forseismic forces, they were reinforced bythe high-ductility steels and performedas a part of a spatial frame. Columns ofsome older buildings have longitudinalreinforcement of plane mild steel whichhas an inherently high survival power. Acertain continuity and redundancy havebeen intuitively provided. Whenanchorage of beams reinforcement wasadequate and shear reinforcementrequired for the gravitational loads wasprovided their performance under a lowintensity earthquake loadings (up to0.10 g) was satisfactory. Usually, abeam's capacities were predeterminedby its connections

Both columns of buildings with "softstories" and "short-rigid columns"incorporated into more flexible R.C.frames have suffered heavy damages.The shearing failure is the mostcommon mode of destruction.Combined effects of shear, eccentricalcompression and torsion resulted inshear cracking, spalling of concrete andbuckling of longitudinal reinforcement atthe top and bottom parts. In some casesthe corrosion of reinforcementaggravated the damage. Beams usuallysuffered some visible, but not life-threatening damages. Flexural andshearing cracks could have a maximumopening of up to 0.6 mm. In somespandrel beams the torsional effectstriggered a shear type cracking.

Roof and floors In most cases the roof and floorsystems can be classified as rigid intheir own plane. But there are cases ofbeams spanning in one direction,chaotic arrangement of beams and lackof their continuity, beams within a slabdepth.

Slabs of 15cm depth, when rigidly fixedinto four supporting beams of adequatedimensions and spans, can effectivelyprovide for the uniform distribution oflateral seismic forces.

Some minor cracking was observed inone-way spanning floor slabs, whensupporting beams were provided in onedirection only.

Other In many cases the basements are notunder the whole area of buildings.More-than-one-level foundations do nothave an appropriate transition zonesfrom one depth to another. Tie-beamsare not always of an adequate capacityto hold pad footings together and toprevent their mutual displacements androtations. These beams supportinfill-walls and are not located at thebottom of footings.

Generally, foundations performedsatisfactorily, except some isolatedcases where uneven settlements andcertain base distortions were

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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)1999 Limassol 5.8 MMI-VII1996 Paphos - Limassol 6.5 MMI-VII-VIII1995 Paphos 5.7 MMI-VII

Additional Comments: Main bulk of destruction was in masonry buildings. Note: the vulnerability rating ofmedium assigned in the previous section reflects the level of seismic hazard officially adopted in Cyprus(i.e. peak ground acceleration of 0.15g). For the higher intensities, this assessment would not be true,and buildings would be expected to be rated in the B category of vulnerability.

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7 Building Materials and Construction Process

7.1 Description of Building MaterialsStructural Element Building Material Characteristic Strength Mix Proportions/ Dimensions CommentsFoundations Concrete 15-20 N/mm²Frame Concrete, Steel 15-25 N/mm², S220-S500Roof and floors Concrete , Steel 15-20 N/mm², S220-S400

Notes:1. Tensile and shear strengths of concrete generally comply with its compressive strength. Steels with thelong yielding plateau were used.2. At present a concrete mix proportion by volume is forbidden, but in the past 1:2:3 - 1:2:4 proportionswere used. Masonry cement mortar mixes were 1:3 - 1:6. Site prepared mortars were of a poor quality.Common dimensions of bricks for the infill walls: 100 X 200 X 300 mm. with the void ratio ofapproximately 40%.Up to the early 1970's the coastal areas contractors were using mainly unwashed sea gravel and sand,which have a high chloride content. In the inland regions the natural river-bed gravel and blends ofcrushed diabase and marine sand were used. Structures of the 1974-1985 period are affected bycarbonation and silica-alkali-reactions. Up to 1983 there were no effective quality control. Low strengthconcrete (approximately 10-15 N/mm² in slabs-beams and 15-20 N/mm² in columns) of high porosity andpermeability have been reported as indicative.

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?Typically these buildings are constructed by developers, but the builders can live in them.

7.3 Construction ProcessUsually developers and contractors have built up these type of buildings.

7.4 Design/Construction ExpertiseAt present a design is to be prepared by the registered engineer and architect. Contracts are awarded onthe tendering basis. Contractors are to be registered with the specified qualification and experience. Inthe past, however, this practice was not followed.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

Title of the code or standard: Before adoption of the National Code of Practice in 1994 the codes of anydeveloped country could be used , provided that a design will be checked and approved by the authority.As a result the following codes have been used: CP114, CP110, BS8110, ACI318, BAEL, DIN , SNiP andsome others.Year the first code/standard addressing this type of construction issued: Beginning of the last century.National building code, material codes and seismic codes/standards: Seismic design and construction ofreinforces concrete structures. 1994. Practically it is a version proposed by the CEB-FIP. But thedescribed here type of buildings does not conform with it.

7.6 Role of Engineers and ArchitectsArchitects are responsible for the architectural planning and drawings. Civil Engineers are responsible forthe structural design The compulsory site-control by engineers have been introduced only in 1999.

7.7 Building Permits and Development Control Rules

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Yes NoBuilding 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: Modifications, alterations and additions are possible. Permissions are to beobtained.

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

Additional Comments: Poor maintenance presents a huge problem.

7.10 Process for Building Code EnforcementThese buildings were constructed before the adoption and enforcement of current Codes. In the past alax inspection and quality control resulted in a shoddy construction which can be rated as one of the maincontributing factors to destructions. At present a site inspection by a structural engineer is compulsory.

7.11 Typical Problems Associated with this Type of ConstructionTorsional vulnerability. Short-column effects. Inadequacy of shear and confining reinforcement.Combination of stiff and flexible structural and non-structural elements. Poor detailing in terms of seismicperformance. (See paragraphs : 4.2 and 5.2).In many instances the depth of carbonation is larger than the cover to reinforcement which itself is ratherfrequently not adequate and sometimes-it does not exist at all. Corrosion of reinforcement andsubsequent cracking of concrete are widespread. In coastal areas the sea-ward sides of buildings areheavily affected by concrete deterioration and the corrosion of reinforcement.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)Approximately 450 US$/m²

8.2 Labor Requirements (estimate)5-6 months for a 4-storey building by the 8-10 person-strong team.

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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

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?

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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 shearing capacity and ductility ofcolumns

1. Steel angles-strips jacketing over the whole height of a column. SeeFig. 7A Strength, stiffness and ductility are all affected. Concrete coveror ganite concrete is added on the top.

Null 2. Traditional R.C. jacketing. See Fig. 7B Existing concrete cover is tobe removed, existing reinforcement is to be cleaned (if needed), newlongitudinal reinforcement should be anchored into foundations andfloors. Closely spaced lateral ties at the top and bottom are to beprovided. Concrete cover should be reinstalled.

Null 3. Confining of concrete by the spiral wire tightly wrapped around acolumn and welded to vertical steel strips. See Fig. 7C

Excessive interstory drift 1. Diagonal bracing. See Fig. 7D.Null 2. Infilling into opening , infilling into frame, infilling of a panel with an

opening. See Fig. 7E.

Additional Comments: A considerable improvement of confining by steel angles jacketing can beachieved by preliminary prestressing of a jacket. Before welding the steel strips are to be heated up to300 deg C, ensuring that at a time of welding their temperature is not lower than 150 deg C. While coolingdown the contraction forces create lateral tightening. The weak point of the steel-angle jacketing is theelectric welds, which are brittle in themselves and commonly are not of an adequate length and capacity.Moreover, an anchorage of angles into floors and foundations is difficult. The joint response of newlyadded angle jackets and existing columns can be significantly improved by prestressing of longitudinalangles by means of lateral bolts tightening ,as it is shown in Fig.7. Before installing angles the lateralnotches are made in them to allow their slight bending. While tightening lateral bolts the angles arestraightened and the vertical thrust forces are transferred to frame beams. Usually one of thesetechniques is used.

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?These methods have been used in several cases.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?Steel angles-strips jacketing,, R.C. jacketing , bracing and infillings were used as the repair-upgradingmeasures following slight damages after earthquakes. A confining of corner columns of circularcross-section by a spiral wire was done as a mitigation effort

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?Contractor. Structural engineer was involved.

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?Satisfactory. There was no strong quake since then, but they stood well to several light tremors.

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11 ReferencesG. Constantinou and K. Solomis. Summery of National experience, lessons learned from earthquakesand assessment of vulnerability in Cyprus. Ministry of Agriculture, National Recourses and Environment.Geological department. 1996.

Construction and housing statistics. Statistical Service of Cyprus, 1999.

I. Kalogeras, G. Stavrakis, and K. Solomis. The October 9,1996 earthquake in Cyprus. Annali diGeofisica, vol.42, N1, February 1999.

Seismicity of Cyprus during the last 100 years. Seismological station. Seismic zones. Microzones.Mitigation policy. Seismic code of practice. Ministry of Agriculture, National Resources andEnvironment.22/5/1997.

C. Chrisostomou., Earthquake in Paphos.23/2/1995. Architect and Civil Engineer. N2, May 1995.

K. Solomis., Earthquake of August 11,1999 in Limassol. Geological Department. 4/4/2000.

K. Ioannidi, G. Stavraki, C. Fringa, A. Kuriaxi and M. Sakhpaxi TEE, N1940. Athens, February 3, 1997.

Seminars, Conferences, Personal communications and practical involvements.

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12 ContributorsName V. LevtchitchTitle ProfessorAffiliation Frederick Institute of TechnologyAddress P.O.Box 24729, p.c.1303City NicosiaZipcodeCountry CyprusPhone +357-2-431355Fax +357-2-438234Email savvas@research. fit.ac.cyWebpage

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13 Figures

FIGURE 1: Typical Building

FIGURE 2: Key Load Bearing Elements

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FIGURE 3: Plan of a Typical Building

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FIGURE 4:Critical Structural Detail

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FIGURE 5A: Soft ground story

FIGURE 5B: Plan and elevation irregularities

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FIGURE 5C: Not symmetrical location of stairwell

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FIGURE 5D: Inadequate seismic joint

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FIGURE 5E: Short stiff columns

FIGURE 5F: Short columns, sharp difference of capacities of adjacent columns

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FIGURE 5G: Excessive length of a cantilever canopy

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FIGURE 5H: Large balconies

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FIGURE 5I: Heavy concentrated loads are transferred to a thin balcony slab

FIGURE 5J: Weak columns, not complete beam-grid and a heavy-rigid parapet wall of the additionallyconstructed top story

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FIGURE 6A: A Photograph Illustrating Typical Earthquake Damage. Shearing failure of a partition

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FIGURE 6B: Diagonal shearing of an infill wall

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FIGURE 6C: Horizontal shearing displacement

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FIGURE 6D: Shearing failure of a short column

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FIGURE 6E: Shearing of concrete and buckling of longitudinal reinforcement due to inadequate lateralreinforcement.

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FIGURE 6F: Torsional shearing and buckling of longitudinal reinforcement at the bottom of a cornercolumn

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FIGURE 6G: Shearing and buckling at the bottom of a column

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FIGURE 6H: Buckling of reinforcement at the bottom of a cylindrical column

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FIGURE 6I: Eccentric beam-short column connection

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FIGURE 6J: Support failure

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FIGURE 7A: Illustration of Seismic Strengthening Techniques

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FIGURE 7B: Traditional R.C. jacketing

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FIGURE 7C: Confining of concrete by spiral wire

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FIGURE 7D: Diagonal bracing

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FIGURE 7E: Infillings. a) Into opening, b) Into frame, c) Steel bracing, d) Panel with opening

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