World Housing Encyclopedia Report

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World Housing Encyclopedia ReportCountry: IndiaHousing Type: Traditional rural house in Kutch region of India (bhonga)Contributors:Madhusudan ChoudharyKishor S. JaiswalRavi SinhaPrimary Reviewer:Mauro SassuCreated on: 6/5/2002Last Modified: 7/2/2003This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions, and recommendations expressed herein are thoseof the various participants, and do not necessarily reflect the views of the Earthquake EngineeringResearch Institute, the International Association for Earthquake Engineering, the Engineering InformationFoundation, John A. Martin & Associates, Inc. or the participants' organizations.

Table of ContentsGeneral Information.1Architectural Features. 5Socio-Economic Issues. 6Structural Features. 8Evaluation of Seismic Performance and Seismic Vulnerability. 12Earthquake Damage Patterns. 16Building Materials and Construction Process. 18Construction Economics.20Insurance.21Seismic Strengthening Technologies. 22References. 23Contributors. 24Figures.25

1 General Information1.1 CountryIndia1.3 Housing TypeTraditional rural house in Kutch region of India(bhonga)1.4 SummaryBhonga is a traditional construction type of theKutch district of Gujarat state in India, which hasa very high seismic hazard. A Bhonga consistsof a single cylindrically shaped room. TheBhonga has a conical roof supported bycylindrical walls. Bhonga construction hasexisted for several hundred years. This type ofhouse is quite durable and appropriate forprevalent desert conditions. Due to itsrobustness against natural hazards as well as itspleasant aesthetics, this type of housing is alsoknown as "Architecture without Architects". Thistype of housing performed very well in the recentM 7.6 Bhuj earthquake of 2001. Very fewBhongas experienced significant damage in theepicentral region, and damage that did occurcan be mainly attributed to poor quality of theconstruction materials or improper maintenanceof the structure. It was also observed that thefailure of Bhongas in the last earthquake causedvery few injuries to the occupants due to thetype of collapse.Figure 1A: Typical Building1.5 Typical Period of Practice for Buildings of This Construction TypeHow long has thisconstruction been practiced 25 years 50 years 75 years 100 years 200 years 200 yearsXIs this construction still being practiced?YesXNoAdditional Comments: Bhongas older than 50 years have been found in Kutch district of Gujarat state inIndia.1.6 Region(s) Where UsedKutch district of Gujarat state in India1.7 Urban vs. Rural ConstructionPage 1

Where is this construction commonly found?In urban areasIn rural areasIn suburban areasBoth in rural and urban areasXAdditional Comments: There is no evidence of Bhongas constructed in urban areas. However, since theBhongas rarely survive for over 50 years, Bhongas constructed in urban areas do not exist any more dueto the prevalence of modern construction materials in urban areas during the last 50 years.Figure 1B: Typical BuildingPage 2

Figure 1C: Typical BuildingFigure 1D: Typical BuildingPage 3

Figure 1E: Typical BuildingFigure 1F: Typical BuildingPage 4

2 Architectural Features2.1 OpeningsA Bhonga generally has only three openings one door and two small windows.2.2 SitingIs this type of construction typically found on flat terrain?Is this type of construction typically found on sloped terrain? (hilly areas)Is it typical for buildings of this type to have common walls with adjacentbuildings?YesXNoXXThe typical separation distance between buildings is 3.0 meters2.3 Building ConfigurationBhonga is circular in plan, with cylindrically shaped walls and topped with conical roof. The inner diameterof the Bhonga is typically between 3m to 6m.2.4 Building FunctionWhat is the main function for buildings of this type?Single family houseMultiple housing unitsMixed use (commercial ground floor, residential above)Other (explain below)XAdditional Comments: Insert additional text if applicable2.5 Means of EscapeMain door of the Bhonga is the only means of escape.2.6 Modification of BuildingsRecent Bhongas constructions have used wide variety of construction materials. These include the stoneor burnt brick masonry either in mud mortar or in cement mortar. Traditional roof consists of light-weightconical roof, while some recent constructions have used heavy manglore tiles on roofs. Some recentconstructions have used circular strip footing below the wall, while traditional construction simplyextended the walls below ground level.Page 5

3 Socio-Economic Issues3.1 Patterns of OccupancyA Bhonga is occupied by a single family. Sometimes, a single family housing unit may consist of severalBhongas. The variation depends on the size and economic condition of the family.3.2 Number of Housing Units in a Building1 units in each building.Additional Comments: Each Bhonga is a single room housing unit. Depending on the economic conditionof the owner, a housing unit may consist of several Bhongas.3.3 Average Number of Inhabitants in a BuildingHow many inhabitants reside in a typical building of thisconstruction type? 55 to 1010-20 20OtherDuring the day / businesshoursXDuring the evening / nightX3.4 Number of Bathrooms or Latrines per Housing UnitNumber of Bathrooms: 0Number of Latrines: 0Additional Comments: Bathroom and laterines are constructed in a separate structure.3.5 Economic Level of InhabitantsEconomic StatusVery poorPoorMiddle ClassRichHouse Price/Annual Income(Ratio)////XX3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner FinancedPersonal SavingsInformal Network: friends and relativesSmall lending institutions/microfinance institutionsCommercial banks / mortagesInvestment poolsCombination (explain)Government-owned housingOtherXX3.7 OwnershipType of Ownership/OccupancyRentOwn outrightOwn with Debt (mortgage or other)Units owned individually (condominium)Owned by group or poolLong-term leaseOtherXPage 6

Figure 3: Plan of a Typical BuildingPage 7

4 Structural Features4.1 Lateral Load-Resisting SystemDue to circular shape of wall in plan, inertial forces developed in wall are resisted through shell actionproviding excellent resistance to lateral forces. In addition, the thick walls required for thermal insulationhave high in-plane stiffness which provides excellent perfomance under lateral loadsThe roofing materials are generally very light weight, and develops low inertia forces. Since the roof isconstructed from extremely ductile materials such as bamboo and straw, the performance of.these roofsis usually very robust. Even in situations where the roof collapses, its low weight ensures that the extentof injuries to occupants is very low. In several Bhongas, the roof joist is not directly supported on thecylindrical walls, but is supported by two wooden vertical posts outside the Bhonga, which furtherimproves seismic resistance of the inetia force generated in the roof.In some instances, reinforcing bands at lintel level and collar level have been used to provide additionalstrength. These bands are constructed from bamboo or from RCC. These increase the lateralload-carrying strength greatly and increase the seismic resistance of the Bhongas.4.2 Gravity Load-Bearing StructureThe conical roof of a Bhonga is supported at its crest by a vertical central wooden post, which rests on awooden joist. The base of the roof and the wooden joist are generally directly supported on Bhonga walls.Sometimes, the roof load on wooden joist is transferred to diametrically placed timber posts (verticalmembers) adjacent to the cylindrical wall. This reduces the roof-load on the walls.The Bhonga wall is usually extended below ground upto the required fundation depth, and separatefoundation is not traditionally constructed. In newer constructions, proper strip footing is also used.Page 8

4.3 Type of Structural SystemMaterialMasonryType ofLoad-BearingStructureStone masonrywalls#123456Unreinforced brick 7masonry walls8Earthen walls9Confined masonry 10Concrete blockmasonry wallsConcreteSteelTimberVarious111213Moment resisting 14frame151617181920Shear wall structure 2122Moment resisting 23frame2425Braced frame2627Load-bearing28timber frame2930313233Seismic protection 34systemsOther35SubtypesRubble stone (field stone) in mud/lime mortar or withoutmortar (usually with timber roof)Massive stone masonry (in lime or cement mortar)Mud wallsMud walls with horizontal wood elementsAdobe block or brick wallsRammed earth/Pise constructionUnreinforced brick masonry in mud or lime mortarUnreinforced brick masonry in mud or lime mortar withvertical postsUnreinforced brick masonry in cement or lime mortar(various floor/roof systems)Confined brick/block masonry with concrete posts/tiecolumns and beamsUnreinforced in lime or cement mortar (various floor/roofsystems)Reinforced in cement mortar (various floor/roof systems)Large concrete block walls with concrete floors and roofsDesigned for gravity loads only (predating seismic codes i.e.no seismic features)Designed with seismic features (various ages)Frame with unreinforced masonry infill wallsFlat slab structurePrecast frame structureFrame with concrete shear walls-dual systemPrecast prestressed frame with shear wallsWalls cast in-situPrecast wall panel structureWith brick masonry partitionsWith cast in-situ concrete wallsWith lightweight partitionsConcentricEccentricThatchPost and beam frameWalls with bamboo/reed mesh and post (wattle and daub)Wooden frame (with or without infill)Stud wall frame with plywood/gypsum board sheathingWooden panel or log constructionBuilding protected with base isolation devices or seismicdampersXAdditional Comments: Many old Bhongas (constructed over 40-50 years) consist of adobe block wallswith mud or lime mortar whereas the walls of recently constructed Bhongas consists of cut stone or claybricks in mud or lime mortar.Page 9

4.4 Type of FoundationTypeDescriptionShallow Foundation Wall or column embedded in soil, without footingRubble stone (fieldstone) isolated footingRubble stone (fieldstone) strip footingReinforced concrete isolated footingReinforced concrete strip footingMat foundationNo foundationDeep Foundation Reinforced concrete bearing pilesReinforced concrete skin friction pilesSteel bearing pilesWood pilesSteel skin friction pilesCast in place concrete piersCaissonsOtherX4.5 Type of Floor/Roof OtherDescription of floor/roof systemVaultedComposite masonry and concrete joistSolid slabs (cast in place or precast)Cast in place waffle slabsCast in place flat slabsPrecast joist systemPrecast hollow core slabsPrecast beams with concrete toppingPost-tensioned slabsComposite steel deck with concrete slabRammed earth with ballast and concrete or plaster finishingWood 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 wallsRandom rubble with mud finishingFloorRoofXXAdditional Comments: Roof is considered to be a flexible diaphragm.4.6 Typical Plan DimensionsAdditional Comments: Inner diameter generally varies between 3.0 m to 6.0 m.4.7 Typical Number of Stories14.8 Typical Story Height2.5 meters4.9 Typical Span6 metersAdditional Comments: Cylindrical wall having an inner diameter of 3 to 6Page 10

4.10 Typical Wall Density25% (totally) since the plan is circular in shape4.11 General Applicability of Answers to Questions in Section 4The answers are for a Bhonga with inner diameter of about 3.0 m. This is the lower-end of typicaldiameter of Bhonga. Bhongas with diameter of up to 6.0 m are also sometimes constructed.Figure 4: Critical Structural DetailsPage 11

5 Evaluation of Seismic Performance and Seismic Vulnerability5.1 Structural and Architectural Features: Seismic ResistanceStructural/ArchitecturalFeatureLateral load pathBuildingconfigurationRoof constructionFloor constructionFoundationperformanceWall and framestructuresredundancyWall proportionsFoundation- wallconnectionWall-roofconnectionsWall openingsQuality of buildingmaterialsQuality ofworkmanshipMaintenanceStatementTrueThe structure contains a complete load path for seismic force effects fromany horizontal direction that serves to transfer inertial forces form thebuilding to the foundation.The building is regular with regards to both the plan and the elevation.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.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.There is no evidence of excessive foundation movement (e.g. settlement)that would affect the integrity or performance of the structure in anearthquake.The number of lines of walls or frames in each principal direction is greaterthan or equal to 2.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).Vertical load-bearing elements (columns, walls) are attached to thefoundations; concrete columns and walls are doweled into the foundation.Exterior walls are anchored for out-of-plane seismic effects at eachdiaphragm level with metal anchors or straps.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.Quality of building materials is considered to be adequate per requirementsof national codes and standards (an estimate).Quality of workmanship (based on visual inspection of few typical buildings)is considered to be good (per local construction standards).Buildings of this type are generally well maintained and there are no visiblesigns of deterioration of building elements (concrete, steel, timber).FalseN/AXXXXXXXXXXXXXOther5.2 Seismic FeaturesStructural Element Seismic DeficiencyEarthquake-Resilient FeaturesWallPoor quality of construction materialsExcellent resistance to lateral loads due(especially the use of adobe blocks and to the shell action of cylindrical walls.mud mortarFrame (Columns,beams)Roof and floorsEarthquake Damage PatternsMinor damage for walls constructed withcement mortar and significant damagefor walls constructed with mud mortarwere observed after Bhuj earthquake.Not ApplicableRoofs are simply supported on thewalls. Sometimes, vertical posts areused to support the wooden joists, butthe connection is not proper.Roofs have good resistance due to their Only minor damage to the roofs werelight weight and use of highly ductileobserved during the Bhuj earthquake,materials.even for Bhongas whose walls hadtotally collapsed. The roof was able tomaintain its structural integrity due to itslight weight and weak connectionbetween the roof and the wall.OtherAdditional Comments: Bhonga is a very unique example of shear-wall building.Page 12

5.3 Seismic Vulnerability RatingHigh (Very PoorSeismicPerformance)ASeismicVulnerability ClassVulnerabilityMediumBC D0E Low (ExcellentSeismicPerformace)F0 - probable value - lower bound - upper boundPage 13

Page 14

Figure 5A: A Photograph Illustrating Typical Earthquake Damage (2001 Bhuj earthquake)Page 15

6 Earthquake Damage Patterns6.1 Past Earthquakes Reported To Affect This ConstructionYearEarthquake EpicenterRichter magnitude(M)02001Bulandshahar (Uttar Pradesh)Bhuj (Gujarat)6.77.6Maximum Intensity (IndicateScale e.g. MMI, MSK)VIII (MSK)X (MSK)FIGURE 6A: A Photograph Illustrating Typical Earthquake Damage (2001 Bhuj earthquake)Page 16

Figure 6B: A Photograph Illustrating Typical Earthquake Damage (2001 Bhuj earthquake)Page 17

7 Building Materials and Construction Process7.1 Description of Building MaterialsStructural Element Building MaterialCharacteristic StrengthWallsStone masonry in -mud mortar (mostcommon for newconstructions),Adobe walls (oldconstructions),Burnt bricks withmud or lime mortarFoundationsSame as wall--FrameRoof and floors--Bamboo, straw and -thatch roofMix Proportions/ Dimensions Comments-Stone masonry inmud mortar (mostcommon for newconstructions),Adobe walls (oldconstructions),Burnt bricks withmud or lime mortar-Usually the wallsare extended to adepth of 1.0 m intothe ground asfoundation---Very light weightand ductileOtherOther7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?In almost all situations, the owner lives in this construction.7.3 Construction ProcessThese constructions are carried out by local village masons. The locally available soft stone can easily becut or chiselled into rectangular blocks, which are used for wall masonry. The local soil is used for mudmortar and to make adobe blocks. Locally available timber and bamboo are used for roof. The entireconstruction process, which is carried out by the mason with very few unskilled labourers, can becompleted within 30 days.7.4 Design/Construction ExpertiseThe construction process uses traditional expertise and understanding of performance of local buildingmaterials.7.5 Building Codes and StandardsYesIs this construction type addressed by codes/standards?NoX7.6 Role of Engineers and ArchitectsNo engineers and architects are involved in the design or construction since this is a traditional housingform which has been in use for several hundred years.7.7 Building Permits and Development Control RulesYesBuilding permits are requiredInformal constructionConstruction authorized per development control rulesNoXXX7.8 Phasing of ConstructionPage 18

YesConstruction takes place over time (incrementally)Building originally designed for its final constructed sizeNoXXAdditional Comments: Bhongas are never "designed" in the modern context. However, Bhongaarchitecture is a very unique aspect of traditional desert architecture of Kutch region in which the size,location and orientation of the Bhonga are planned for very good structural and functional results.7.9 Building MaintenanceWho typically maintains buildings of this type?BuilderOwner(s)Renter(s)No oneOtherX7.10 Process for Building Code EnforcementNot applicable since rural constructions do not require building code compliance.7.11 Typical Problems Associated with this Type of ConstructionThese structures are not very durable due to the use of mud mortar. The use of light-weight roof alsocauses problems during cyclone season. Several instances of roof damage after cyclonic winds arereported every year. However, due to its light weight, the flying roof debris do not cause major secondarydamage.Figure 7: Illustration of Seismic Strengthening TechniquesPage 19

8 Construction Economics8.1 Unit Construction Cost (estimate)Rs 160 per sq m (US 4 per sq m) per house in the case of a conventional Bhonga constructed usingsun-dried brick, mud and thatch roof.Rs. 1075 per sq m (US 23 per sq m) per house in the case of a Bhonga constructed using a single layerthick burnt brick wall in cement mortar, and with timber conical roof.8.2 Labor Requirements (estimate)Only unskilled or semi-skilled labour is required for its construction.Page 20

9 Insurance9.1 Insurance IssuesYesEarthquake insurance for this construction type is typically availableInsurance premium discounts or higher coverages are available for seismicallystrengthened buildings or new buildings built to incorporate seismically resistantfeaturesNoXX9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?Page 21

10 Seismic Strengthening Technologies10.1 Description of Seismic Strengthening ProvisionsType of intervention Structural DeficiencyRetrofitLow resistance to lateral loads(Strengthening)Weak roof support systemWeak roof support systemDescription of seismic strengthening provision usedProviding seismic bandage between lintel and roof levels on bothoutside and inside of the wall.Providing additional joists to transfer roof load to the cylindrical walls.Providing new vertical post adjacent to walls (on the outside) tosupport the roof joist.New ConstructionUsing cement mortar and stone or burnt brick masonry for walls.Constructing seismic bands at lintel and roof levels to enhance wallstiffness to lateral loads and to also improve shear resistance nearcorner of openingsProviding vertical post adjacent to walls (on the outside) to supportroof joinstsProviding several joists to transfer roof load to the cylindrical walls orvertical posts.Low resistance to lateral loadsLow resistance to lateral loadsWeak roof support systemWeak roof support system10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?No, seismic strengthening of Bhongas has not been carried out.10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?Not applicable.10.4 Was the construction inspected in the same manner as new construction?No formal structural inspection is done for either new or rehabilitated constructions.10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?In these rural constructions, technically trained personnel are seldom available. Most constructions arecarried out by skilled or semi-skilled persons only.10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?No data is available. However, new constructions with earthquake-resistant features performed very wellcompared to Bhongas without any earthquake-resistant features. The performance of these Bhongas wascomparable to that of RCC frame structures in the epicentral region.Page 22

11 ReferencesSinha, R. et al., The Bhuj earthquake of January 26, 2001, Indian Institute of Technology, Bombay, April2001 (available at http://www.civil.iitb.ac.in/BhujEarthquake/Cover Page.htm).Page 23

12 CountryPhoneFaxEmailWebpageMadhusudan ChoudharyKishor S. JaiswalRavi SinhaGraduate StudentResearch StudentAssociate ProfessorIndian Institute of Technology, IIT BombayIIT BombayBombayDepartment of CivilCivil Engineering Department, Civil EngineeringEngineering, IIT PowaiIndian Institute of Technology DepartmentIndian Institute ofTechnology, PowaiMumbaiPowai MumbaiMumbai400 076400 076400 076IndiaIndiaIndia 91-22-572-2545 Ext. 8389 91-22-5722545 ext. 8389(91-22) 576-7336(91-22) 572-3480, ac.inrsinha@civil.iitb.ac.inPage 24

13 FiguresFigure 1A: Typical BuildingPage 25

World Housing Encyclopedia Report Country: India Housing Type: Traditional rural house in Kutch region of India (bhonga) Contributors: Madhusudan Choudhary Kishor S. Jaiswal Ravi Sinha Primary Reviewer: Mauro Sassu Created on: 6/5/2002 Last Modified: 7/2/2003 This encyclopedia contains info

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