Report: 117

Building Type: Unreinforced Masonry Building : Brick masonry in mud/lime mortar, with vertical posts

Country: Iran

Author(s): Nima T. Bekloo, NA

Last Updated:

Regions Where Found: Buildings of this construction type can be found in all parts of the Persian Empire, especially next to the desert(Kavir). This type of housing construction is commonly found in both rural and sub-urban areas.

Summary: The 'Four arches' or Char Taaqi (in Persian) derives its name from the four arches thatconnect the tops of four timber or masonry piers enclosing the space. It is an equilateralarchitectural unit consisting of four arches or short Barrel vaults between four corner piers,with a dome over the central square; this square and the lateral bays under the arches or barrelvaults together constitute a room of cruciform ground plan. This structural system developedabout 2500 years ago, after the earring system in the Old Persian Empire (Sasanian age). The maingoal of this building system was to create wide openings at four side of the structure. Thisbuilding system was used for special places that carry high population like fire temple (placewhere Persians worshiped the Fire God), mosque, bazaar and other public places. It is notthat difficult to built a dome over four arches. Further, dome structures are ideal for large spanstructures against gravity loads as it transforms them into horizontal and shear loads. Inaddition, for lateral loads, domes behave like a truss and distribute the load to other parts ofthe structure developing a perfect load path. This construction system has been considered the most prominent structural system in traditional Iranian architecture. These are basicallymonumental buildings developed close to the desert where there was not enough constructionmaterials that could take tensile stresses.

Length of time practiced: More than 200 years

Still Practiced: No

In practice as of: Unknown

Building Occupancy: Institutional housingOther

Typical number of stories: 1

Terrain-Flat: Typically

Terrain-Sloped: Occasionally

Comments: This construction system was common in the past formonumental building structures.

Plan Shape: Square, solidRectangular, solid

Additional comments on plan shape: This building is square in the plan. This type of building has also been constructed with other plan shapes as wellhowever, then the name would be different.

Typical plan length (meters): 7-30

Typical plan width (meters): 7-30

Typical story height (meters): 7-20

Type of Structural System: Masonry: Earthen/Mud/Adobe/Rammed Earth Walls: Mud wallsMasonry: Earthen/Mud/Adobe/Rammed Earth Walls: Adobe block wallsMasonry: Earthen/Mud/Adobe/Rammed Earth Walls: Rammed earth/pile constructionMasonry: Unreinforced Masonry Walls: Brick masonry in mud/lime mortarMasonry: Unreinforced Masonry Walls: Brick masonry in mud mortar with vertical posts

Additional comments on structural system: Lateral load-resisting system: The lateral load-resisting system is huge masonry piers connected by the arches at the topand the dome-roof system.Gravity load-bearing system: The vertical load-resisting system is earthen walls: huge masonry piers connected by the arches at the top and the dome-roof system.

Gravity load-bearing & lateral load-resisting systems: Plaster of paris was one of the materials that was used for the mortar.

Typical wall densities in direction 1: >20%

Typical wall densities in direction 2: >20%

Additional comments on typical wall densities: The typicalstructural wall density is more than 20 %. 15% to 30%.

Wall Openings: Large openings are provided in all four sides in between huge pierslocated at the corners. Sometimes an opening is also provided in the roof for natural light. These are usually around 50cm in diameter.

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Modifications of buildings: Some modifications could have been made in the roof opening and the shapes of the arches over time. The roofopenings could have been made smaller or larger, and the arches modified as shown in figures.

Type of Foundation: Shallow Foundation: Wall or column embedded in soil, without footingShallow Foundation: Rubble stone, fieldstone isolated footingShallow Foundation: Rubble stone, fieldstone strip footing

Additional comments on foundation:

Type of Floor System: Wooden beams or trusses and joists supporting heavy flooring

Additional comments on floor system: Vaulted Masonry; The construction materials have no ductility. With building it in vault form, the forces distribute on surface.

Type of Roof System: Masonry roof, unknownVaulted masonry roofShallow-arched masonry roofEarthen roof, unknownVaulted earthen roofRoof system, other

Additional comments on roof system: Vaulted Masonry; The construction materials have no ductility. With building it in vault form, the forces distribute on surface.

Additional comments section 2: These buildings do not share common walls with adjacent buildings; theyare mostly free standing buildings. However, sometimes when these are built in the middle of other buildings (as intersection), there is no gap between adjacent buildings. This building type was used as public places like temples, mosques, street or bazaar, intersections, public baths, ormaybe sometimes as house of an important person because with this technique the house could be constructedbigger and higher. In a typical building of this type, there are no elevators and no fire-protected exitstaircases. Depending on the building function, there could be up to four exits on all four sides.

Who is involved with the design process? ArchitectTechnologistBuilderOther

Roles of those involved in the design process: There were no academically qualified engineers or architects and no standard codes for design of this type of buildingstructures were available. These might have been constructed by empiricism or experimentation. However, it is still atopic of research.

Expertise of those involved in the design process: There are no academically qualified engineers or architects for this type of buildings.

Who typically builds this construction type? MasonBuilderOther

Roles of those involved in the building process: Experienced persons, master builders and maybe some contractors with help of laborers built the structure.

Expertise of those involved in building process:

Construction process and phasing: Tools/equipment typically used: shovel, hack, float and other old construction equipment.The construction of this type of housing takes place in asingle phase. Typically, the building is not originally designed for its final constructed size.

Construction issues:

Is this construction type address by codes/standards? No

Applicable codes or standards:

Process for building code enforcement:

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: This is a historic building typology and is not being constructed anymore, except for creating the pastarchitecture of Persia. Building permits are not required to build this housing type.

Typical problems associated with this type of construction: Since These types are ancient, sometimes they clash with urban developement

Who typically maintains buildings of this type? BuilderOwner(s)Other

Additional comments on maintenance and building condition: Sometimes the governormaintains the building.

Unit construction cost: Approximately US$70-80 /m2.

Labor requirements: 5-15 people for about 6-12 month depending on the size of the building

Additional comments section 3:

Patterns of occupancy: Public places, for small to large population. Each dome-roofprovides cover to one large platform at ground level.

Number of inhabitants in a typical building of this construction type during the day: >20

Number of inhabitants in a typical building of this construction type during the evening/night: 10-20

Additional comments on number of inhabitants:

Economic level of inhabitants: Middle-income classHigh-income class (rich)

Additional comments on economic level of inhabitants: Economic Level: The ratio of price of housing unit to the annual income can be 1:1 for middle class families.

Typical Source of Financing: Personal savingsInformal network: friends or relativesGovernment-owned housingOther

Additional comments on financing: Government from taxes or people of an area gathered and built -for example- a public bath or mosque.

Type of Ownership: Own outrightOwned by group or poolOther

Additional comments on ownership: It is a public building owned by the government or people of the area.

Is earthquake insurance for this construction type typically available?: Yes

What does earthquake insurance typically cover/cost: Earthquake insurance is included in fire insurance and it is based on the value of thebuilding.Depends on the owner capital demand, usually for every US$5000 additional cover, it costs about US$6/year added to fire insurance. That is what the insurance company quotes, however, these structures are now parts ofthe governors' properties.

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: Yes

Additional comments on premium discounts:

Additional comments section 4:

Damage patterns observed in past earthquakes for this construction type: As stated above this type has been constructed thousands years ago, hence there must have been many otherearthquakes especially the historical ones that affected these buildings. However, information in not available.

Additional comments on earthquake damage patterns: Overall damage patterns observed in past earthquakes for this type of construction included crushing of brick material and:(frame): diagonal cracks more often in mortar, shearand tensile failure at the column bottom (roof and floors): No significant damage except that causedby column failure(other): Crushing of brick material

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.

Additional comments on structural and architectural features for seismic resistance:

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: SetbackChange in vertical structureOther

Seismic deficiency in walls: Brittle material, mostly no confinements

Earthquake-resilient features in walls: Vaulted roof and massive masonry piers.

Seismic deficiency in frames: Constructed of low strength brittle materials, the structuralelements are unreinforced.

Earthquake-resilient features in frame: Well defined load path, highrigidity

Seismic deficiency in roof and floors: Constructed of low strength brittle materials, heavy inweight, the roof is unreinforced, opening in the roof, largespan

Earthquake resilient features in roof and floors: Well defined load path, perfectdistribution of forces andstresses

Seismic deficiency in foundation: Lack of Lateral resistance

Earthquake-resilient features in foundation: N/A

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

Additional comments section 5: This type of structure has continuous load path like concrete columns with concrete shell connecting the columns atthe top, except that bricks and mortars do not have that material properties.

Additional comments on seismic strengthening provisions: Unreinforced arch - Reinforcing of the arch by prestressed with cable or steel bar at spring level

Has seismic strengthening described in the above table been performed?: No

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?: They are used for both issues.

Was the construction inspected in the same manner as new construction?: No.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?: Government.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?: N/A

Additional comments section 6: The construction materials used in these buildings do not comply with the Iranian codes.

• History of engineering in IranFarshad,M.Balkh Publications 1997

• Iranian retrofitting provision for existing buildings : Section 7 - Masonry structures and infillsIIEES

• Iran insurance co., http://www.iraninsurance.ir

• Earthquake Engineering Theory and ApplicationsMoghaddam,H.Farahang Publication 2002

• Siamak Ahi webblog, http://chaartaagh.blogspot.com/