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 #:177
Building Type: Adobe Arched-Roof
Country: Iran
Author(s): Mohammad Yekrangnia
Ali Bakhshi
Mohammad Ali Ghannad
Arash Khosravifar
Ebrahim Mousavi Eshkiki
Hamid Masaeli
Last Updated:
Regions Where Found: This typology can be found in arid and semi-arid areas, mostly in rural regions of Iran including Kerman, Southern Khorasan and Yazd provinces. Especially in the past, this structural type was the most abundant in these areas. Nowadays, brick masonry buildings with jack-arch roof are the most prevalent building typology in these regions. Moreover, these buildings constitute more than 2% out of a total of five million rural houses throughout the country.
Summary:

This construction type is a single-family house which is found ...

Length of time practiced: More than 200 years
Still Practiced: Off
In practice as of:
Building Occupancy: Single dwelling; Residential, 2 units; Mixed residential/commercial
Typical number of stories: one
Terrain-Flat: Off
Terrain-Sloped: Off
Comments: Even with the recent great changes to the big cities in Iran with respect to construction types and development, some arched-roo


 

Features

 

 

Plan Shape Rectangular, solid; Rectangular, with an opening in plan
Additional comments on plan shape Depending on the roof system, the plan shape of the building can be square or rectangular. Polygonal and dome roofs usually necessitate a squared plan shape, while the crescent, barrel and complex (Tagh-o-lenge) roofs are associated with a rectangular plan.
Typical plan length (meters) 6
Typical plan width (meters) 4
Typical story height (meters) 3
Type of Structural System Masonry: Earthen/Mud/Adobe/Rammed Earth Walls: Adobe block walls
Additional comments on structural system These buildings were constructed considering gravity loads only, and thick adobe walls can reliably transfer these loads to the ground. The arched roofs, although considered as heavy roof systems, can safely transfer their weight to the supporting walls. The arching mechanism of these roofs helps their stability against either gravity or seismic lateral forces as well. Although in some cases, deterioration of the shallow foundations was observed, no damages due to inadequate foundation capacity were reported. Adobe buildings in Iran possess no lateral load-resisting system and are therefore classified as 'non-engineered' houses. Although thick and squat walls have great in-plane and out-of-plane seismic capacity, they also induce considerable seismic demands due to their huge mass. On the other hand, since no special provisions have been given for load-transfer mechanisms between roof and walls and also between perpendicular walls, compromised structural integrity usually results in partial or complete collapse of these buildings (Figure 5).
Gravity load-bearing & lateral load-resisting systems
Typical wall densities in direction 1 10-15%
Typical wall densities in direction 2 5-10%
Additional comments on typical wall densities Wall density greatly depends on the wall thickness and plan dimensions. Wall density is larger in buildings with squared plan shape.
Wall Openings There are three types of openings in these structures: doors, windows, and shelves. The shelves are similar to the windows except that they are not through-wall openings. In other words, their depth is usually half of the walls' thickness. They are used for decoration purposes. The average area of doors, windows and shelves are 1.9m.sq., 2.2m.sq., and 2.1m.sq., respectively. Either wooden lintel or arch (more common in arched roof adobe buildings) are provided above openings (Figure 6).
Is it typical for buildings of this type to have common walls with adjacent buildings? Off
Modifications of buildings In some cases, extensions to the original houses are found, usually for adding more rooms for the newlyweds or for other functions, e.g. stable.
Type of Foundation Shallow Foundation: Wall or column embedded in soil, without footing
Additional comments on foundation As stated by Mousavi Eshkiki (2006), the foundation, in its best form, is limited to about 50 cm of digging the ground and filling it with lime-sand mortar and stones or the wall materials up to the ground level. Generally, foundation construction is mostly affected by the topography of the site and the soil conditions, and it is usually neglected during construction, unless in regions with very loose (organic) soils.
Type of Floor System No elevated or suspended floor system (single-story building)
Additional comments on floor system
Type of Roof System Vaulted earthen roof
Additional comments on roof system The material of arched roofs greatly depends on the structural specifications. In polygonal, dome and vaulted roofs, only adobe blocks are used, while in the crescent (Tagh-o-lenge) roofs, wooden ties are usually applied. These roofs are 30 to 50 cm thick and have a mass per unit area from 450 to 750 kg/sqm. Over time, several additional protective layers are mounted on top of these roofs which make them heavier due to aging process (Figure 7).
Additional comments section 2 The plan dimensions are related to the area under each arched roof. A cluster of several rooms (having a roof each) with the dimensions of 20 m can exist. Also, story height ranges from 2.8 m to 3.2 m (Figure 8).

 

Building Materials and Construction Process

 

 

Description of Building Materials


Structural Element Building Material (s)Comment (s)
Wall/Frame Sun-dried adobe blocksCompressive strength of masonry prism:5-28 kg/cm2; Shear strength of mud mortar: 0.04-0.15 kg/cm2; Density 1,800 kg/m3; Mix proportion of clay-sand of the mortar is 5:1 but this varies a lot in different regions
Foundations N.A.
Floors N.A.
Roof Sun-dried adobe blocksCompressive strength of masonry prism: 5-28 kg/cm2; Shear strength of mud mortar: 0.04-0.15 kg/cm2; Density 1,800 kg/m3; Mix proportion of clay-sand of the mortar is 5:1 but this varies a lot in different regions
Other

Design Process


Who is involved with the design process? Builder; Owner
Roles of those involved in the design process There is no special design process for these buildings. The construction details are finalized by experienced masons based on the owner's needs.
Expertise of those involved in the design process Masons' expertise is mainly developed through experience and it is transferred in the family over several generations.

Construction Process


Who typically builds this construction type? Mason
Roles of those involved in the building process The construction process is mainly performed by experienced and specialized masons.
Expertise of those involved in building process The expertise of the masons mainly originated from experience and from generation to generation.
Construction process and phasing The construction process is carried out under the direct supervision of the building owner. The construction process starts with producing adobe blocks and sun-drying them (Figure 9), excavating the ground, and placing a few courses of adobe masonry if a shallow foundation is provided. Next, the walls are built first and then the arched roof is constructed. The final step involves finishing of the walls and especially the roof with mud-straw overlay.
Construction issues The main construction issues related to the seismic vulnerability of these buildings are poor connections between the perpendicular walls, and also the connection between the roof and the supporting walls.

Building Codes and Standards


Is this construction type address by codes/standards? Off
Applicable codes or standards
Process for building code enforcement

Building Permits and Development Control Rules


Are building permits required? Off
Is this typically informal construction? Off
Is this construction typically authorized as per development control rules? Off
Additional comments on building permits and development control rules

Building Maintenance and Condition


Typical problems associated with this type of construction
Who typically maintains buildings of this type? Owner(s)
Additional comments on maintenance and building condition Usually, it is the owner who maintains the building, but given the low economic levels of the owners there is generally little or no maintenance and over time the construction deteriorates.

Construction Economics


Unit construction cost The unit construction cost for this housing type ranges from 10 to 50 USD/sqm. However, it is difficult to estimate the cost as the construction of this building type is rare nowadays.
Labor requirements The construction requires approximately three skilled workers and it takes up to about 2-3 months. The mason(s) involved in construction need(s) to have experience with respect to the building site selection, architectural requirements, and need(s) to be knowledgeable about the proper mix proportions for manufacturing the adobe blocks.
Additional comments section 3

 

Socio-Economic Issues

 

 

Patterns of occupancy Since these buildings are found in arid and semi-arid areas (deserts), they are often found in the form of cluster houses concentrated around a main yard. A housing unit is typically occupied by a single family, or sometimes by an extended family (two generations of the same family). In general, there may be up to 20 housing units in each building (Figure 10).
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 10-May
Additional comments on number of inhabitants Since a considerable number of adobe houses in Iran are in the form of cluster houses, the total number of inhabitants in one complex can reach up to 100 persons. However, the average number of inhabitants in each housing unit is 5 people. Moreover, in case of an earthquake, the entire cluster behaves as a single building since there are common walls between these housing units.
Economic level of inhabitants Low-income class (poor)
Additional comments on economic level of inhabitants
Typical Source of Financing Owner financed
Additional comments on financing
Type of Ownership Own outright
Additional comments on ownership
Is earthquake insurance for this construction type typically available? Off
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? Off
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
2003Bam, Kerman Province
2005Zarand, Kerman Province
6.6X-XI (EMS-98)
6.4X-XI (EMS-98)

Past Earthquakes


Damage patterns observed in past earthquakes for this construction type In 2003, the Bam earthquake struck Bam and the surrounding Kerman province of south-eastern Iran with a moment magnitude Mw 6.6. The earthquake was particularly destructive, with a death toll amounting to 26,271 people and injuring an additional 30,000. The effects of the earthquake were exacerbated by the use of mud bricks as the standard construction material. The earthquake left an estimated 100,000 people homeless. An important regional center during the 16th and 17th centuries, Bam contained many buildings that were not constructed to survive earthquake effects. Many houses in Bam were owner-built, and the owners did not use the help of skilled labor or proper building materials to resist earthquakes in the construction. The Bam Citadel was considered to be one of the most significant existing mud citadels before the event. Most of it was demolished in the earthquake, including a large square tower (Wikipedia.org). In 2005, the Zarand earthquake hit the city of Zarand and several villages in Kerman province of Iran. The earthquake was measured at 6.4 on the Richter scale. The quake lasted for 11 seconds and at least 61 aftershocks were reported with magnitudes between 3.3 and 4.8. The maximum recorded peak ground acceleration was 0.51g at Shirinrud Dam. Though ISNA reports, 790 dead and 1,423 injured according to officials in Kerman University of Medical Sciences. Four villages, each having around 1,000 inhabitants, were reported completely destroyed, and 30 to 70% of buildings in more than 40 villages were reported damaged (Wikipedia.org). As for adobe houses which formed the majority of the housing in rural and suburban areas in the both aforementioned regions, the common failure mode was destabilization of the arched roof due to poor connection of the perpendicular walls as shown in Figure 2-1, Figure 4-a, Figure 5-a and Figure 11.
Additional comments on earthquake damage patterns Walls experience detachment from each other and from the roof. Sliding in the form of bed-joint and diagonal is common. For barrel, crescent and complex arched roofs where two walls are load-bearing, the other two usually experience out-of-plane overturning (Figure 13).

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.FALSE
Building Configuration-VerticalThe building is regular with regards to the elevation. (Specify in 5.4.1)N/A
Building Configuration-HorizontalThe building is regular with regards to the plan. (Specify in 5.4.2)FALSE
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.N/A
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. FALSE
Wall and Frame Structures-RedundancyThe number of lines of walls or frames in each principal direction is greater than or equal to 2.TRUE
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.FALSE
Wall-Roof ConnectionsExterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. FALSE
Wall OpeningsFALSE
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).FALSE

Additional comments on structural and architectural features for seismic resistance In many cases, there is no foundation in these buildings (Figure 11). In some cases, rubble stones are found at the base of the walls and in some cases under the ground level in order to act as moisture insulator. Deterioration of the walls and wall bases have been observed due to weathering and moisture (Figure 12) as stated by Webster et al. In some cases, especially those found in suburban areas, the maintenance of the houses is acceptable. Moreover, those which have been constructed recently are kept in good condition. However, in rural areas, the quality of the existing arched-roof houses are poor due to deterioration of adobe mainly because of weathering and also cracks in the walls and the dome from previous earthquakes.
Vertical irregularities typically found in this construction type Torsion eccentricity
Horizontal irregularities typically found in this construction type Other
Seismic deficiency in walls Walls have a great potential in tolerating seismic forces both in in-plane and out-of-plane directions because of their low height/length aspect ratio and height/thickness slenderness ratio. However, since no special attention has been given to ensure the connection of perpendicular walls, these walls separate from each other during an earthquake and this results in partial or complete roof collapse.
Earthquake-resilient features in walls In rare cases, parallel walls are connected by means of steel rods. This provision was found to be very effective in preventing detachment of walls and hence maintaining 'box-like' behavior. Adobe walls are thicker and shorter than their brick counterparts and hence possess greater load-bearing capacity. Also, considering high surcharges, their in-plane behavior is governed by friction due to low cohesion of mud mortar, hence their response is more ductile than brick walls with sand-cement mortar. Also, since in many cases the openings are arch-shaped (no lintel is used), no diagonal cracks are initiated at the openings (Figure 14).
Seismic deficiency in frames N.A.
Earthquake-resilient features in frame N.A.
Seismic deficiency in roof and floors The main concern about the roofs is their attachment to the supporting walls which in many cases are weak. However, this weakness cannot result in roof collapse per se provided that 'box-like' behavior of the building has been guaranteed.
Earthquake resilient features in roof and floors The arched roofs are expected to maintain their integrity because of arching action. Their seismic performance is superior to wooden flat roofs. Besides the arching action, other reasons for good seismic resistance are their lighter weight and more uniform distribution of roof surcharge on the walls. Dome and polygonal roofs transmit their weight to four walls, while in other roof systems, these loads are placed on two walls and the remaining two walls are non-load-bearing.
Seismic deficiency in foundation N.A.
Earthquake-resilient features in foundation N.A.

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 The cluster pattern of single building units improves their strength and integrity during earthquake.

Retrofit Information

 

 

Description of Seismic Strengthening Provisions


Structural Deficiency Seismic Strengthening
Detachment of perpendicular walls Using four steel rods in each direction to attach parallel walls. These rods were used in a few retrofit projects and proved to be effective in past earthquakes (Figure 15). The rods can easily pass through the drilled holes in the walls.
Cracking in walls (in-plane) Installing steel welded mesh on the exterior faces of walls. The mesh is attached with through-wall connections bolted on the other side of the wall. Also it is enough to place the mesh only on the upper half of the wall and without any shotcrete; only a proper coating is needed in order to prevent the deterioration of the steel (Figure 15). This strengthening technique is also very simple to implement since it does not require any concrete covering.

Additional comments on seismic strengthening provisions
Has seismic strengthening described in the above table been performed? Retrofitting of adobe houses was practiced on few pilot examples throughout the country as a pilot project. The final goal was to execute a major retrofitting project for similar rural houses and several thousand school buildings of Iran by the State Organization of Schools Renovation Development and Mobilization. As of this writing (2014), this project is underway under supervision, and technical and financial assistance of the Housing Foundation of Islamic Revolution.
Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Adobe buildings showed two distinct performances during past earthquakes; severe damages or collapse and no major damages. The former needed demolition and probably replacement of the structural type and the latter needed retrofitting as a mitigation program.
Was the construction inspected in the same manner as new construction?
Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? A structural engineer and two skilled workers involved in the retrofit design and execution, respectively. The construction is carried out by a contractor appointed by the master (provincial Housing Foundation offices).
What has been the performance of retrofitted buildings of this type in subsequent earthquakes? The seismic performance of the retrofitted adobe houses has not yet been observed in earthquakes. However, shake-table studies performed in Iran proved that the proposed retrofitting system is very effective in preventing collapse of the model building even against Maximum Considered Earthquake (MCE) with a PGA of 0.92g based on Bakhshi et al. (2009).
Additional comments section 6

 

References


Alalhesabi, M. (1993). Patterns of rural houses, Housing Foundation of Islamic Revolution, Tehran, Iran.



Bakhshi, A., Ghannad, M.A., Yekrangnia, M., and Masaeli, H. (2009). Seismic Performance of Existing and Retrofitted Dome-Roof Adobe Houses in Iran using Shaking Table Tests, PEER 2009/02, October 2009, Proceedings of a U.S.-Iran Seismic Workshop , June 29-July 1, 2009, Irvine, California.



California Institute of Earth Art and Architecture, http://www.calearth.org



European Macroseismic Scale 1998. European Seismological Commission, Subcommission on Engineering Seismology, Working Group Macroseismic scales, 1998.



Hejazi, M., and Mehdizadeh Saradj, F. (2013). Persian Architectural Heritage: Form, Structure and Conservation, WIT Press, Southampton and Boston, 2013.



Mousavi, Eshkiki S.E., Khosravifar, A., Ghannad, M.A., Bakhshi, A., Taheri Behbahani, A.A., and Bozorgnia, Y. (2006). Structural Typology of Traditional Houses in Iran based on their Seismic Behavior, Proceedings of the 8th U.S. National Conference on Earthquake Engineering, April 18-22, 2006, San Francisco, California, US.



Webster, F., and Tolles, E. (2000). Earthquake damage to historic and older adobe buildings during the 1994 Northridge, California Earthquake, Proceedings of the 12th World Conference on Earthquake Engineering, 2000.



http://en.wikipedia.org/wiki/2003_Bam_earthquake; http://en.wikipedia.org/wiki/2005_Zarand_earthquake



Zamrashidi, H. (1995). Architecture of Iran - Construction of traditional houses, Zomorrod Publications, Tehran, Iran.


Authors







Name Title Affiliation Location Email
Mohammad Yekrangnia Ph.D. Candidate Sharif Univ. of Tech. Azadi St., Tehran, Iran m.yekrangnia@gmail.com
Ali Bakhshi Associate Prof. Sharif Univ. of Tech. Azadi St., Tehran, Iran bakhshi@sharif.edu
Mohammad Ali Ghannad Prof. Sharif Univ. of Tech. Azadi St., Tehran, Iran ghannad@sharif.edu
Arash Khosravifar M.Sc. Graduate Sharif Univ. of Tech. Azadi St., Tehran, Iran
Ebrahim Mousavi Eshkiki M.Sc. Graduate Sharif Univ. of Tech. Azadi St., Tehran, Iran
Hamid Masaeli M.Sc. Graduate Sharif Univ. of Tech. Azadi St., Tehran, Iran

Reviewers


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