Description

The World Housing Encyclopedia (WHE) Report Database contains 130 reports on housing construction types in 43 seismically active countries. Each housing report is a detailed description of a housing type in a particular country. The description is prepared from a number of standard closed-ended questions and some narrative that have been provided by report authors. Each report has five major categories including architectural and structural features; Building Materials and Construction Process; Socio-economic Issues; Past Performance In Earthquakes, Seismic Features and Vulnerability; and Retrofit. All of the housing reports in this database have been contributed by volunteers. If you are interested in writing a housing report please contact the WHE Editorial Board.

About

The World Housing Encyclopedia (WHE) is a collection of resources related to housing construction practices in the seismically active areas of the world. The mission is to share experiences with different construction types and encourage the use of earthquake-resistant technologies worldwide. The technical activities of the WHE are steered by an international team of 22 professionals specializing in different aspects of seismic safety of buildings and structures. They bring relevant experience from 16 seismically active countries across the world. For more information about the World Housing Encyclopedia, visit http://www.world-housing.net/.

General Information

 

Report #:72
Building Type: Traditional rural house in Kutch region of India (bhonga)
Country: India
Author(s): Madhusudan Choudhary
Kishor Jaiswal
Ravi Sinha
Last Updated:
Regions Where Found: Buildings of this construction type can be found in Kutch district of Gujarat state in India. This type of housing construction is commonly found in rural areas. There is no evidence of Bhongas constructed in urban areas. However, since the Bhongas rarely survive for over 50 years, Bhongas constructed in urban areas do not exist any more due to the prevalence of modern construction materials in urban areas during the last 50 years.
Summary:

The Bhonga is a traditional construction type in the Kutch ...

Length of time practiced: More than 200 years
Still Practiced: Yes
In practice as of:
Building Occupancy: Single dwelling
Typical number of stories: 1
Terrain-Flat: Typically
Terrain-Sloped: 3
Comments: Bhongas older than 50 years have been found in Kutch district of Gujarat state in India.


 

Features

 

 

Plan Shape Curved, solid (e.g. circular, elliptical, ovoid)
Additional comments on plan shape Inner diameter generally varies between 3.0 m to 6.0 m..
Typical plan length (meters) 6 meters
Typical plan width (meters) 6 meters
Typical story height (meters) 2.5 meters
Type of Structural System Masonry: Earthen/Mud/Adobe/Rammed Earth Walls: Adobe block walls
Additional comments on structural system The conical roof of a Bhonga is supported at its crest by a vertical central wooden post, which rests on a wooden 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 (vertical members) adjacent to the cylindrical wall. This reduces the roof-load on the walls. The Bhonga wall is usually extended below ground up to the required foundation depth, and separate foundation is not traditionally constructed. In newer constructions, proper strip footing is also used. Due to circular shape of wall in plan, inertial forces developed in wall are resisted through shell action providing excellent resistance to lateral forces. In addition, the thick walls required for thermal insulation have high in-plane stiffness which provides excellent performance under lateral loads The roofing materials are generally very light weight, and develops low inertia forces. Since the roof is constructed from extremely ductile materials such as bamboo and straw, the performance of these roofs is usually very robust. Even in situations where the roof collapses, its low weight ensures that the extent of injuries to occupants is very low. In several Bhongas, the roof joist is not directly supported on the cylindrical walls, but is supported by two wooden vertical posts outside the Bhonga, which further improves 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 additional strength. These bands are constructed from bamboo or from RCC. These increase the lateral load-carrying strength greatly and increase the seismic resistance of the Bhongas.
Gravity load-bearing & lateral load-resisting systems Many old Bhongas (constructed over 40-50 years) consist of adobe block walls with mud or lime mortar whereas the walls of recently constructed Bhongas consists of cut stone or clay bricks in mud or lime mortar.
Typical wall densities in direction 1 >20%
Typical wall densities in direction 2 >20%
Additional comments on typical wall densities 25% (totally) since the plan is circular in shape.
Wall Openings A Bhonga generally has only three openings one door and two small windows.
Is it typical for buildings of this type to have common walls with adjacent buildings? No
Modifications of buildings Recent Bhongas constructions have used wide variety of construction materials. These include the stone or burnt brick masonry either in mud mortar or in cement mortar. Traditional roof consists of light-weight conical roof, while some recent constructions have used heavy manglore tiles on roofs. Some recent constructions have used circular strip footing below the wall, while traditional construction simply extended the walls below ground level.
Type of Foundation Shallow Foundation: Wall or column embedded in soil, without footing
Additional comments on foundation
Type of Floor System Other floor system
Additional comments on floor system Random rubble with mud finishing.
Type of Roof System Roof system, other
Additional comments on roof system Thatched roof supported on wood purlins Roof is considered to be a flexible diaphragm.
Additional comments section 2 Typical separation between buildings is 3.0 meters. The typical span of the roofing/flooring system is 6 meters.

 

Building Materials and Construction Process

 

 

Description of Building Materials


Structural Element Building Material (s)Comment (s)
Wall/Frame Stone masonry in mud mortar (most common for new constructions), Adobe walls (old constructions), Burnt bricks with mud or lime mortar Stone masonry in mud mortar (most common for new construction), Adobe walls (old construction), Burnt bricks with mud or lime mortar
Foundations Same as wallUsually the walls are extended to a depth of 1.0m into the ground as foundation
Floors Bamboo, straw and thatch roofVery light weight and ductile.
Roof Bamboo, straw and thatch roofVery light weight and ductile.
Other

Design Process


Who is involved with the design process? Other
Roles of those involved in the design process In almost all situations, the owner lives in this construction. No engineers and architects are involved in the design or construction since this is a traditional housing form which has been in use for several hundred years.
Expertise of those involved in the design process

Construction Process


Who typically builds this construction type? OwnerMason
Roles of those involved in the building process In almost all situations, the owner lives in this construction.
Expertise of those involved in building process These constructions are carried out by local village masons. The construction process uses traditional expertise and understanding of performance of local building materials.
Construction process and phasing These constructions are carried out by local village masons. The locally available soft stone can easily be cut or chiselled into rectangular blocks, which are used for wall masonry. The local soil is used for mud mortar and to make adobe blocks. Locally available timber and bamboo are used for roof. The entire construction process, which is carried out by the mason with very few unskilled laborers, can be completed within 30 days. The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size. Bhongas are never "designed" in the modern context. However, Bhonga architecture 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.
Construction issues

Building Codes and Standards


Is this construction type address by codes/standards? No
Applicable codes or standards
Process for building code enforcement Not applicable since rural constructions do not require building code compliance.

Building Permits and Development Control Rules


Are building permits required? No
Is this typically informal construction? Yes
Is this construction typically authorized as per development control rules? No
Additional comments on building permits and development control rules

Building Maintenance and Condition


Typical problems associated with this type of construction These structures are not very durable due to the use of mud mortar. The use of light-weight roof also causes problems during cyclone season. Several instances of roof damage after cyclonic winds are reported every year. However, due to its light weight, the flying roof debris do not cause major secondary damage.
Who typically maintains buildings of this type? Builder
Additional comments on maintenance and building condition

Construction Economics


Unit construction cost Rs 160 per sq m (US $4 per sq m) per house in the case of a conventional Bhonga constructed using sun-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 layer thick burnt brick wall in cement mortar, and with timber conical roof.
Labor requirements Only unskilled or semi-skilled labour is required for its construction.
Additional comments section 3

 

Socio-Economic Issues

 

 

Patterns of occupancy A Bhonga is occupied by a single family. Sometimes, a single family housing unit may consist of several Bhongas. The variation depends on the size and economic condition of the family. Each Bhonga is a single room housing unit. Depending on the economic condition of the owner, a housing unit may consist of several Bhongas.
Number of inhabitants in a typical building of this construction type during the day <5
Number of inhabitants in a typical building of this construction type during the evening/night 5-10
Additional comments on number of inhabitants
Economic level of inhabitants Very low-income class (very poor)Low-income class (poor)
Additional comments on economic level of inhabitants Ratio of housing unit price to annual income: 1:1 or better
Typical Source of Financing Owner financedInformal network: friends or relatives
Additional comments on financing
Type of Ownership Own outright
Additional comments on ownership
Is earthquake insurance for this construction type typically available? No
What does earthquake insurance typically cover/cost
Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features? No
Additional comments on premium discounts
Additional comments section 4

 

Earthquakes

 

 

Past Earthquakes in the country which affected buildings of this type


YearEarthquake Epicenter Richter Magnitude Maximum Intensity
2001Bhuj (Gujarat)
1819Bulandshahar (Uttar Pradesh)
7.6X (MSK)
6.7VIII (MSK)

Past Earthquakes


Damage patterns observed in past earthquakes for this construction type The earthquakes of 1819 and 2001 caused widespread devastation. Adequate reliable information on the performance of Bhonga during the 1819 earthquake is not available. However, during the 2001 earthquake, Bhonga constructions performed at least as well as modern masonry constructions with cement mortar and RCC roof.
Additional comments on earthquake damage patterns Minor damage for walls constructed with cement mortar and significant damage for walls constructed with mud mortar were observed after Bhuj earthquake. Only minor damage to the roofs were observed during the Bhuj earthquake, even for Bhongas whose walls had totally collapsed. The roof was able to maintain its structural integrity due to its light weight and weak connection between the roof and the wall.

Structural and Architectural Features for Seismic Resistance


The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.
Structural/Architectural Feature Statement Seismic Resistance
Lateral load pathThe structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation.TRUE
Building Configuration-VerticalThe building is regular with regards to the elevation. (Specify in 5.4.1)TRUE
Building Configuration-HorizontalThe building is regular with regards to the plan. (Specify in 5.4.2)TRUE
Roof ConstructionThe roof diaphragm is considered to be rigid and it is expected that the roof structure will maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area.FALSE
Floor ConstructionThe floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) will maintain its integrity during an earthquake of intensity expected in this area.FALSE
Foundation PerformanceThere is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-RedundancyThe number of lines of walls or frames in each principal direction is greater than or equal to 2.N/A
Wall ProportionsHeight-to-thickness ratio of the shear walls at each floor level is: Less than 25 (concrete walls); Less than 30 (reinforced masonry walls); Less than 13 (unreinforced masonry walls);TRUE
Foundation-Wall ConnectionVertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation.TRUE
Wall-Roof ConnectionsExterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. FALSE
Wall OpeningsTRUE
Quality of Building MaterialsQuality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). FALSE
Quality of WorkmanshipQuality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards).FALSE
MaintenanceBuildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber).N/A

Additional comments on structural and architectural features for seismic resistance
Vertical irregularities typically found in this construction type No irregularities
Horizontal irregularities typically found in this construction type No irregularities
Seismic deficiency in walls Poor quality of construction materials (especially the use of adobe blocks and mud mortar)
Earthquake-resilient features in walls Excellent resistance to lateral loads due to the shell action of cylindrical walls.
Seismic deficiency in frames N/A
Earthquake-resilient features in frame
Seismic deficiency in roof and floors Roofs are simply supported on the walls. Sometimes, vertical posts are used to support the wooden joists, but the connection is not proper.
Earthquake resilient features in roof and floors Roofs have good resistance due to their light weight and use of highly ductile materials.
Seismic deficiency in foundation
Earthquake-resilient features in foundation

Seismic Vulnerability Rating


For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

High vulnerabilty Medium vulnerabilityLow vulnerability
ABCDEF
Seismic vulnerability class |- o -|

Additional comments section 5 Bhonga is a very unique example of shear-wall building.

Retrofit Information

 

 

Description of Seismic Strengthening Provisions


Structural Deficiency Seismic Strengthening
Low resistance to lateral loads Providing seismic bandage between lintel and roof levels on both outside and inside of the wall.
Weak roof support system Providing additional joists to transfer roof load to the cylindrical walls.
Weak roof support system Providing new vertical post adjacent to walls (on the outside) to support the roof joist.
New Construction: Low resistance to lateral loads Using cement mortar and stone or burnt brick masonry for walls; Constructing seismic bands at lintel and roof levels to enhance wall stiffness to lateral loads and to also improve shear resistance near corner of openings
New Construction: Weak roof support system Providing vertical post adjacent to walls (on the outside) to support roof joints; Providing several joists to transfer roof load to the cylindrical walls or vertical posts.

Additional comments on seismic strengthening provisions
Has seismic strengthening described in the above table been performed? No, seismic strengthening of Bhongas has not been carried out.
Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Not applicable.
Was the construction inspected in the same manner as new construction? No formal structural inspection is done for either new or rehabilitated constructions.
Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? In these rural constructions, technically trained personnel are seldom available. Most constructions are carried out by skilled or semi-skilled persons only.
What has been the performance of retrofitted buildings of this type in subsequent earthquakes? No data is available. However, new constructions with earthquake-resistant features performed very well compared to Bhongas without any earthquake-resistant features. The performance of these Bhongas was comparable to that of RCC frame structures in the epicentral region.
Additional comments section 6

 

References

Sinha, R. et al., The Bhuj earthquake of January 26, 2001, Indian Institute of Technology, Bombay, April 2001 (available at http://www.civil.iitb.ac.in/BhujEarthquake/Cover_Page.htm).




Authors




Name Title Affiliation Location Email
Madhusudan Choudhary Graduate Student Indian Insitute of Technology, Bombay Department of Civil Engineering, IIT Powai, Mumbai 400 076 India madhu@civil.iitb.ac.in
Kishor Jaiswal Graduate Student Indian Insitute of Technology, Bombay Department of Civil Engineering, IIT Powai, Mumbai 400 076 India rskishor@civil.iitb.ac.in
Ravi Sinha Associate Professor Indian Insitute of Technology, Bombay Department of Civil Engineering, IIT Powai, Mumbai 400 076 India rsinha@civil.iitb.ac.in

Reviewers


Name Title Affiliation Location Email
Mauro Sassu Associate Professor Dept. of Structural Engineering, University of Pisa Pisa 56126, ITALY m.sassu@ing.unipi.it