World Housing Encyclopedia Report

Country: Romania

Housing Type: Reinforced concrete frame structure with diagonal bracings and brickinfill walls

Contributors:Maria Bostenaru DanIlie Sandu

Primary Reviewer:Vanja Alendar

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........................................................................................ 3Socio-Economic Issues...................................................................................... 4Structural Features............................................................................................. 5Evaluation of Seismic Performance and Seismic Vulnerability.......................... 9Earthquake Damage Patterns............................................................................ 11Building Materials and Construction Process..................................................... 12Construction Economics.....................................................................................14Insurance............................................................................................................15Seismic Strengthening Technologies................................................................. 16References......................................................................................................... 18Contributors........................................................................................................ 19Figures................................................................................................................20

1 General Information

1.1 CountryRomania

1.3 Housing TypeReinforced concrete frame structure withdiagonal bracings and brick infill walls

1.4 SummaryThis is a Post-World War II variant of thewell-known Romanian 'inter-bellum' building.This urban housing construction was practicedin Romania over a rather short period of time,after the World War II until the nationalization in1947. Buildings of this type are still in use,mainly as apartment buildings. Buildings aretypically 7 to 11 stories high and the mainload-bearing structure consists of a reinforcedconcrete space frame with reinforced concretediagonal bracings. The floor structure consists ofRC solid slabs and beams cast in place. Theframes are infilled with brick masonry walls(typical wall thickness 140 mm or 280 mm).These buildings were designed according to thetemporary guidelines issued in 1941 by theMinistry of Public Works (MLP); the guidelineswere based on the German recommendations.This region is well known as a seismically pronearea, with the epicenter of damagingearthquakes close to Vrancea. Earthquakes withthe Richter magnitude of over 7.0 occur once in30 years. Bucharest, the capital, is locatedaround 150 km south of the epicenter and lies inthe main direction of the propagation of seismicwaves. The Bucharest area is located on thebanks of the Dâmbovita and Colentina river, onnon-homogenous alluvial soil deposits. Duringthe earthquake of 4 March 1977 (Richtermagnitude 7.2), over 30 buildings collapsed inBucharest, killing 1,424 people. It should benoted that buildings of this construction type hadexperienced severe damage, mainly cracking inthe columns and the brick masonry infill walls,however collapse was not reported. After the1977 Vrancea earthquake, the damagedbuildings were repaired and strengthened. Oneof the example buildings described in thiscontribution was retrofitted by strengthening theexisting columns with new reinforced concretejackets and replacing the existing brick masonryinfill walls with new lightweight concrete blockwalls. It should be noted that the diagonalbracings were removed as a part of the retrofit.Another example shows a triangular-shapedbuilding with the original bracing preserved

FIGURE 1A: Typical Building

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during the retrofit.

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

Is this construction still being practiced? Yes NoX

Additional Comments: Blocks of apartments of this type were built after the World War II until thenationalization in 1947. Period of practice was less than 5 years.

1.6 Region(s) Where UsedThere are a few existing buildings of this type in Bucharest. These buildings were retrofitted after the 1977earthquake and they are still in use.

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

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2 Architectural Features

2.1 OpeningsThere is one window in each room. The windows in these buildings are much wider than in theirpredecessors, the inter-bellum buildings. The width of a window is equal to 60% of the wall length, andthe total area of windows constitutes up to 24% of the wall surface area. Each room has a door; howeverin this building type doors constitute less than 30% of the wall surface area.

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 meters

2.3 Building ConfigurationMostly rectangular, with notable exceptions; for example, a building with triangular-shaped plan is shownin this contribution.

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)

2.5 Means of EscapeOne elevator for 4 persons, and the 1.30 m wide stairs. There are 2 dwellings per floor and the building istypically 5-story high.

2.6 Modification of BuildingsThe dwellings have been modified after the 1978 retrofit, however the modifications vary from building tobuilding and it is hard to generalize. The building plan presented in this contribution was recorded basedon the actual condition in November 2001. Neither the original (as constructed) building plan nor the plansexisting at the time of the 1977 earthquake are available. It is known that, in general, the new inhabitantsafter 1948 made their own modifications, and did not follow the regulations concerning the building space.Modifications of the building interior arrangement and in the structural elements were made as a part ofthe retrofit following the 1977 earthquake. Details of the modifications are not available.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyOne family per housing unit, and two housing units per floor.

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

Additional Comments: The number varies from 10-20; there are two units per floor

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 1010-20> 20Other X X

Additional Comments: About 4 inhabitants per housing unit

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

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

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

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 / mortagesInvestment poolsCombination (explain)Government-owned housingOther

3.7 OwnershipType of Ownership/OccupancyRentOwn outright XOwn with Debt (mortgage or other)Units owned individually (condominium)Owned by group or poolLong-term leaseOther

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4 Structural Features

4.1 Lateral Load-Resisting SystemThe main load-bearing structure consists of a reinforced concrete space frame with reinforced concretediagonal bracings and masonry infill walls. The floor structure consists of two-way RC solid slabssupported by beams cast in place. The masonry infill walls are 140 mm or 280 mm thick and they areconsidered as nonstructural walls. In some buildings of this type the braces were removed as a part of theretrofit. Figures 5A and 5D illustrate possible bracing layout.

4.2 Gravity Load-Bearing StructureReinforced concrete frame supported by two-way slabs on beams. Although the brick infill walls are notconsidered a part of the load-bearing structure, these walls carry an increased gravity load in the courseof time, due to the reduced load-bearing capacity of reinforced concrete structure caused by thecorrosion.

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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)

15 Designed with seismic features (various ages) X16 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

Moment resistingframe

35 Reinforced concrete frame with concrete diagonal bracings X

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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: The columns are supported by the individual (isolated) footings tied with thebeams.

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: Floor and roof structures are two-way solid slabs with beams.

4.6 Typical Plan DimensionsAdditional Comments: Width varies from 15 to 20 m

4.7 Typical Number of Stories5 - 8

4.8 Typical Story Height2.75 meters

4.9 Typical Span4 meters

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Additional Comments: The wall span is rather non-uniform.

4.10 Typical Wall DensityThe main load-bearing system is concrete frame, and the information regarding wall density is notrelevant.

4.11 General Applicability of Answers to Questions in Section 4This contribution describes a case study of a typical building of this construction 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

5.2 Seismic FeaturesStructural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsInfill walls - Irregular wall layout; - Too heavy

walls; - Walls not a part of theload-bearing structure; - Wide openings

- Very rigid; might be of assistance tothe frame structure to behave as a dual(frame-wall) system

-The brick masonry infill walls weredamaged in the 1977 earthquake (crackwidth over 0.3 mm).

Frame (columns,beams)

- Irregular layout - Designed according to the Germaninstructions, which provided only basicseismic design provisions

-The example building was affected bythe 1977 earthquake. Over 30% of thecolumns were cracked.

Roof and floors - No significant deficiency -Behave as rigid diaphragm - No significant damage observedBracings - A lateral load bearing capacity

comparable to the capacity of infillmasonry wall wasn't reached.

- The bracings played the key role inprotecting the buildings from collapse inthe 1977 earthquake.

- The bracings were severely damagedin the 1977 earthquake. They wereeffective in resisting seismic effects, andas a result concrete cover has spalledoff. It was considered that the braceswere damaged beyond repair and thatthe retrofitting would prove inefficient.Therefore, the bracings were removedas a part of the retrofit.

Additional Comments: The structural role of the infill walls was neglected in the original design performedaccording to the 1941 temporary guidelines for seismic design.

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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)1986 Vrancea 7 8 (MMI)1990 Vrancea 6.7 7 (MMI)

Additional Comments: No damages to the buildings of this type were observed in the 1986 and 1990earthquakes. In the 1977 earthquake (M 7.2), no significant damages were observed on other buildings ofsimilar construction (as discussed in Section 5.2).

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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 brick masonry infill

wallsbrick dimensions280 X 140 X 70 mm

Foundations reinforced concrete N/AFrame reinforced concrete 28-day cube compressive

strength Quality A= 21.0 MPaCommercial steel yieldstrength = 240 MPa

N/A

Roof and floors reinforced concrete N/A

Notes:1. According to the "Provisions for the design and construction of reinforced concrete buildings" issued bythe Ministry for Public Works and Telecommunications in 1942 following the study of the effects of the1940 earthquake, the concrete used for engineering works incl. civil buildings had to satisfy the required28-day cube compressive strength: Concrete of quality A = 21.0 MPa; Concrete of quality B = 16.5 MPa;Concrete of quality C = 12.0 MPa. Higher strengths were permitted only for the quality A concrete andonly for the structures designed and supervised by experienced engineers. Steel reinforcementproperties: Commercial steel yield strength = 240.0 MPa; superior steel yield strength = 360.0 MPa.2.

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?Information not available.

7.3 Construction ProcessThere were no data available about the original construction which took place in 1946. The retrofit wascompleted by specialized teams, with adequate background and technical skills.

7.4 Design/Construction ExpertiseInformation not available.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

Title of the code or standard: "Provisions for the Design and Construction of Reinforced ConcreteBuildings" (contained seismic provisions based on the German recommendations)Year the first code/standard addressing this type of construction issued: 1942National building code, material codes and seismic codes/standards: P100-78 (contains seismicprovisions)-used for the evaluation of buildings damaged in the 1977 earthquake P100-92 "Standard forseismic design of residential, public, agricultural and industrial buildings"When was the most recent code/standard addressing this construction type issued? 1992

7.6 Role of Engineers and ArchitectsInformation not available.

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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Additional Comments: This construction practice is no longer followed.

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)No oneOther

7.10 Process for Building Code EnforcementInformation not available.

7.11 Typical Problems Associated with this Type of ConstructionInformation not available.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)Information not available.

8.2 Labor Requirements (estimate)Information not available.

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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: ADAS insurance available.

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)

Almost 30% of the total number ofcolumns were cracked

Jacketing of columns with reinforced concrete (see AdditionalComments and Figures 7A, 7B and 7C); As a result of the jacketing,the original column size (450 X 450 mm) was increased to 600 mm X600 mm. The jacketed columns are shown in yellow color in Figure 3B.

Cracking of brick masonry infill walls(crack width over 0.3 mm)

-Replacing the damaged brick masonry infill walls with the lightweightconcrete block infill walls.

Severely damaged RC bracing The damaged bracings were removed. The original position ofbracings is shown in Figure 3B (blue lines). It should be noted that thebracings were not removed in all buildings of this type. The bracingswere not removed in the buildings that suffered less damage in the1977 earthquake.

Additional Comments: Seismic strengthening of deficient concrete columns was accomplished using ajacketing technique. It is very important to achieve an adequate connection between the existing and newconcrete. The following solutions can be applied: (a) Anchorage by means of new ties connecting newand existing reinforcement. Welding is not necessary, however chipping off the concrete cover in theexisting column is required (in order to enable passing of hooks of the new ties). (b) Connection by meansof bent bars welded to the vertical reinforcement. The concrete must be chipped off locally, in order toexpose the vertical reinforcement bars in the areas where bent bars are going to be provided. In this way,concrete keys capable of transmitting shear forces are formed and the force transfer between the existingand the new concrete is achieved. (c) Welding of additional ties to the existing column. The concretecover in the tie region must be removed and each new tie must be welded to the existing one. The abovedescribed solutions are also presented in the UNIDO (1983) publication. Dritsos (2000) provides detailsabout steps followed in applying one-sided RC jacketing. RC jacketing solution likely to have beenadopted in this case is shown in the FEMA 172 publication, as illustrated in Figures 7B and 7C.

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Yes.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?The work was done as post-earthquake rehabilitation following the March 1977 Vrancea earthquake. Dueto the severe damage the building was evacuated and supported on temporary shoring immediately afterthe earthquake and was retrofitted in 1978. The buildings were built in 1946/47 and became stateproperty (nationalization) in 1948. The owners were evacuated; the institutions were changed frequently,while the buildings were also modified. The documents in the archives were lost or are not accessible.The data and drawings required to understand the original design would have to be obtained fromtechnicians practicing at the time. Neither the construction drawings for the original design, nor the retrofitproject drawings were available.

10.4 Was the construction inspected in the same manner as new construction?The construction was inspected according to the current codes (P100-78).

10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?After the 1977 earthquake the retrofit design was developed by the "Institute for Building Design (IPC)".The design has referred to the 1941 Temporary Instructions of the MLP used in the original design andthe then current standard P100-78, which contained seismic design criteria. Specialist architects and civilengineers were involved in the retrofit design.

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10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?The earthquakes in 1986 and 1990 did not cause any damage to the retrofitted buildings.

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11 ReferencesUNIDO (1983). Repair and Strengthening of Reinforced Concrete, Stone and Brick Masonry Buildings.Volume 5, Building Construction Under Seismic Conditions in the Balkan Region, UNDP/UNIDO ProjectRER/79/015, United Nations Industrial Development Organization, Vienna, Austria.

FEMA 172 (1992). NEHRP Handbook of Techniques for the Seismic Rehabilitation of Existing Buildings,Building Seismic Safety Council, Washington, D.C., figures 3.1.2.2b

Dritsos, Stefanos (2000). "Retrofit of Reinforced Concrete Buildings" (in Greek), The University of Patras,Greece, p. 212.

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12 ContributorsName Maria Bostenaru Dan Ilie SanduTitle Dipl.-Ing. Ing.Affiliation Institute for Technology & Management

in Construction, Universitat ofKarlsruhe, Graduate Research Center450

Address Am Fasanengarten, Geb 50.31, Room115

City Karlsruhe BucharestZipcode 76128Country Germany RomaniaPhone +49 721 608 4121Fax +49 721 695 245Email maria.bostenaru@tmb.uni-karlsruhe.deWebpage http://www.natkat.org/maria/

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13 Figures

FIGURE 1A: Typical Building

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FIGURE 1B: Typical Building

FIGURE 2A: Key Load-Bearing Elements

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FIGURE 2B: Perspective Drawing Showing Exterior of the Building

FIGURE 2C: Perspective Drawing Showing Exterior of the Building

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FIGURE 3A: Plan of a Typical Building

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FIGURE 3B: Plan of a Typical Building (after the retrofit)- the jacketed columns are yellow-colored

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FIGURE 4A: Critical Structural Details - Frame with Diagonal Braces and Masonry Infill

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FIGURE 4B: Critical Structural Details - Frame with Diagonal Bracings and Masonry Infill

FIGURE 5A: An Illustration of Key Seismic Features

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FIGURE 5B: Key Seismic Features - RC frame with Bracings

FIGURE 5C: Key Seismic Features-Vertical Section

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FIGURE 5D: Perspective Drawing Showing Key Seismic Features

FIGURE 6: A photo showing a damaged brace panel in the 1977 earthquake (Balan et al. 1982)

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FIGURE 7A: Illustration of Seismic Strengthening Techniques

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FIGURE 7B: Seismic Strengthening Techniques: Cross-Section of a Jacketed Column (Source: FEMA172)

FIGURE 7C: Seismic Strengthening Techniques - Installation of RC Concrete Jacket (Source: FEMA172)

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FIGURE 8A: Another Example of a Typical Building (triangular plan, suffered minor damage in the 1977earthquake)

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FIGURE 8B: A Building with a Triangular Plan - a Perspective Drawing Showing Key Load-BearingElements

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FIGURE 8C: A Building With a Triangular Plan - Perspective Drawing Showing Key Load-BearingElements

FIGURE 8D: Typical Triangular Floor Plan

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FIGURE 8E: Typical Triangular Floor Plan with Balconies

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