| Report # | 117 |
| Report Date | 26-05-2007 |
| Country | IRAN |
| Housing Type | Unreinforced Masonry Building |
| Housing Sub-Type | Unreinforced Masonry Building : Brick masonry in mud/lime mortar, with vertical posts |
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Author(s)
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Nima T. Bekloo |
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Reviewer(s)
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Important
This encyclopedia contains information contributed by various earthquake engineering professionals around the world. All opinions, findings, conclusions & recommendations expressed herein are those of the various participants, and do not necessarily reflect the views of the Earthquake Engineering Research Institute, the International Association for Earthquake Engineering, the Engineering Information Foundation, John A. Martin & Associates, Inc. or the participants' organizations.
Summary
The “Four arches” or Char Taaqi (in Persian) derives its name from the four arches that connects tops of four timber or masonry piers enclosing the space. It is an equilateral architectural 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 barrel vaults together constitute a room of cruciform ground plan. This structural system developed about 2500 years ago, after earring system in the Old Persian Empire (Sasanian age). Main goal of this building system was to create wide openings at four side of the structure. This building system was used for special places that carry high population like fire temple (place where Persians worshiped the Fire God), mosque, bazaar and other public places. This is not that difficult to built a dome over four arches. Further, dome structures are ideal for large span structures against gravity loads as it transforms them into horizontal and shear loads. In addition, for lateral loads, domes behave like a trusse and distribute the load to other parts of the structure developing a perfect load path. This construction system has been considered, the most prominent structural system in traditional Iranian architecture. These are basically monumental buildings developed close to desert where there was not enough construction materials that could take tensile stresses.
1. General Information
Buildings of this construction type can be found in This structural system is common throughout the Persian Empire, especially next to the desert (Kavir). This type of housing construction is commonly found in both rural and sub-urban areas. This construction type has been in practice for more than 200 years ago.
Currently, this type of construction is not being practiced. This construction system was common in the past for monumental building structures.
Figure 1: Typical building (shrine in Aqda, province of Yazd). | 
Figure 2: Another typical building (this is a Niasar fire temple, constructed approximately 0 A.D., in the village of Niasar, near Kashan in the province of Isfahan). | 
Figure 3: Perspective Drawing Showing Key Load-Bearing Elements |
Figure 4: Perspective Drawing Showing Key Load-Bearing Elements | 
Figure 5: Plan of a Typical Building
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Figure 6: 1- Cracks in the dome-roof (it may not have been caused by an earthquake). Photo from Kerman bazaar, in the city of Kerman. |
Figure 7: 2- Vertical crack on thick column (pier). This is from a structure built around 0 A.D. in the city of Bam, province of Kerman. | 
Figure 8: 3- Collapse of the structure due to non ductile materials (Bam earthquake, 2003, IRAN) This is the Kerman bazaar in the city of Kerman. | 
Figure 9: An Illustration of Key Seismic Features and/or Deficiencies. This is a building built around 0 A.D. in the city of Bam, province of Kerman. |
Figure 10: Roof opening for natural light because of lack of electricity in the past . This is the Ganjali khan bath in the city of Kerman. | 
Figure 11: Modification and strengthening technique of arches. This is the Toqrol Tower, built around 400 A.D., in the city of Ray, province of Tehran. | 
Figure 12: The holes that carry the timber tie beams to prevent slipping the roof. This building is located in the city of Aqda, province of Yazd. |
Figure 13: Modern structure based on principles of older Persian architecture. This is Azadi Square, built in the 1970's, in the city of Tehran. | 
Figure 14: Section. Building built around 0 A.D. in Bam, province of Kerman. | 
Figure 15: A Samanian king's house in Bukhara
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2. Architectural Aspects2.1 Siting
These buildings are typically found in flat terrain. They have common walls with adjacent buildings. These are 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 When separated from adjacent buildings, the typical distance from a neighboring building is 0 meters.
2.2 Building Configuration
This building is square in the plan. This type of building has also been constructed with other plan shapes as well however, then the name would be different. Large openings are provided in all four sides in between huge piers located at the corners. Sometimes an opening is also provided in the roof for natural light. These are usually around 50 cm in diameter.
2.3 Functional Planning
This building type was used for public places like temples, mosques, street or bazaar, intersections, public baths, or may be sometimes as house of an important person, because with this technique the house could be constructed bigger and higher. In a typical building of this type, there are no elevators and no fire-protected exit staircases. Depending on the building function, there could be up to four exits on all four sides.
2.4 Modification to Building
Some modifications could have been made in the roof opening and the shapes of the arches over the time. The roof opening could have been made smaller or larger, and the arches modified as shown in figures.
3. Structural Details3.1 Structural System
| Material | Type of Load-Bearing Structure | # | Subtypes | Most appropriate type |
| Masonry | Stone Masonry
Walls | 1 | Rubble stone (field stone) in mud/lime
mortar or without mortar (usually with
timber roof) | ☐ |
| 2 | Dressed stone masonry (in
lime/cement mortar) | ☐ |
| Adobe/ Earthen Walls | 3 | Mud walls | ☐ |
| 4 | Mud walls with horizontal wood elements | ☐ |
| 5 | Adobe block walls | ☐ |
| 6 | Rammed earth/Pise construction | ☐ |
Unreinforced masonry
walls | 7 | Brick masonry in mud/lime
mortar | ☐ |
| 8 | Brick masonry in mud/lime
mortar with vertical posts | ☑ |
| 9 | Brick masonry in lime/cement
mortar | ☐ |
| 10 | Concrete block masonry in
cement mortar | ☐ |
| Confined masonry | 11 | Clay brick/tile masonry, with
wooden posts and beams | ☐ |
| 12 | Clay brick masonry, with
concrete posts/tie columns
and beams | ☐ |
| 13 | Concrete blocks, tie columns
and beams | ☐ |
| Reinforced masonry | 14 | Stone masonry in cement
mortar | ☐ |
| 15 | Clay brick masonry in cement
mortar | ☐ |
| 16 | Concrete block masonry in
cement mortar | ☐ |
| Structural concrete | Moment resisting
frame | 17 | Flat slab structure | ☐ |
| 18 | Designed for gravity loads
only, with URM infill walls | ☐ |
| 19 | Designed for seismic effects,
with URM infill walls | ☐ |
| 20 | Designed for seismic effects,
with structural infill walls | ☐ |
| 21 | Dual system – Frame with
shear wall | ☐ |
| Structural wall | 22 | Moment frame with in-situ
shear walls | ☐ |
| 23 | Moment frame with precast
shear walls | ☐ |
| Precast concrete | 24 | Moment frame | ☐ |
| 25 | Prestressed moment frame
with shear walls | ☐ |
| 26 | Large panel precast walls | ☐ |
| 27 | Shear wall structure with
walls cast-in-situ | ☐ |
| 28 | Shear wall structure with
precast wall panel structure | ☐ |
| Steel | Moment-resisting
frame | 29 | With brick masonry partitions | ☐ |
| 30 | With cast in-situ concrete
walls | ☐ |
| 31 | With lightweight partitions | ☐ |
| Braced frame | 32 | Concentric connections in all
panels | ☐ |
| 33 | Eccentric connections in a
few panels | ☐ |
| Structural wall | 34 | Bolted plate | ☐ |
| 35 | Welded plate | ☐ |
| Timber | Load-bearing timber
frame | 36 | Thatch | ☐ |
| 37 | Walls with bamboo/reed mesh
and post (Wattle and Daub) | ☐ |
| 38 | Masonry with horizontal
beams/planks at intermediate
levels | ☐ |
| 39 | Post and beam frame (no
special connections) | ☐ |
| 40 | Wood frame (with special
connections) | ☐ |
| 41 | Stud-wall frame with
plywood/gypsum board
sheathing | ☐ |
| 42 | Wooden panel walls | ☐ |
| Other | Seismic protection systems | 43 | Building protected with base-isolation systems | ☐ |
| 44 | Building protected with
seismic dampers | ☐ |
| Hybrid systems | 45 | other (described below) | ☐ |
Plaster of paris was one the materials that was used for the mortar.
3.2 Gravity Load-Resisting System
The vertical load-resisting system is earthen walls. Huge masonry piers connected by the arches at the top and dome-roof system.
3.3 Lateral Load-Resisting System
The lateral load-resisting system is others (described below). Huge masonry piers connected by the arches at the top and dome-roof system.
3.4 Building Dimensions
The typical plan dimensions of these buildings are: lengths between 7 and 30 meters, and widths between 7 and 30 meters. The building is 1 storey high. The typical span of the roofing/flooring system is 3-15 meters. Typical Plan Dimensions: The building plan size depends on the building function (intersection, mosque…). The plan dimensions may vary, but in overall the structure have a regular plan.
Typical Story Height: It depends on the building function.
Typical Span: single span for the single roof. The typical storey height in such buildings is 7-20 meters. The typical structural wall density is more than 20 %. 15% to 30%.
3.5 Floor and Roof System
| Material | Description of floor/roof system | Most appropriate floor | Most appropriate roof |
| Masonry | Vaulted | ☑ | ☑ |
Composite system of concrete joists and
masonry panels | ☐ | ☐ |
| Structural concrete | Solid slabs (cast-in-place) | ☐ | ☐ |
| Waffle slabs (cast-in-place) | ☐ | ☐ |
| Flat slabs (cast-in-place) | ☐ | ☐ |
| Precast joist system | ☐ | ☐ |
| Hollow core slab (precast) | ☐ | ☐ |
| Solid slabs (precast) | ☐ | ☐ |
Beams and planks (precast) with concrete
topping (cast-in-situ) | ☐ | ☐ |
| Slabs (post-tensioned) | ☐ | ☐ |
| Steel | Composite steel deck with concrete slab
(cast-in-situ) | ☐ | ☐ |
| Timber | Rammed earth with ballast and concrete or
plaster finishing | ☐ | ☐ |
| Wood planks or beams with ballast and concrete or plaster finishing | ☐ | ☐ |
| Thatched roof supported on wood purlins | ☐ | ☐ |
| Wood shingle roof | ☐ | ☐ |
| Wood planks or beams that support clay tiles | ☐ | ☐ |
Wood planks or beams supporting natural
stones slates | ☐ | ☐ |
Wood planks or beams that support slate,
metal, asbestos-cement or plastic corrugated
sheets or tiles | ☐ | ☐ |
Wood plank, plywood or manufactured wood
panels on joists supported by beams or walls | ☐ | ☐ |
| Other | Described below | ☑ | ☑ |
The construction materials have no ductility. With building it in vault form, the forces distribute on surface.
3.6 Foundation
| Type | Description | Most appropriate type |
| Shallow foundation | Wall or column embedded in
soil, without footing | ☑ |
Rubble stone, fieldstone
isolated footing | ☐ |
Rubble stone, fieldstone strip
footing | ☐ |
Reinforced-concrete isolated
footing | ☐ |
Reinforced-concrete strip
footing | ☐ |
| Mat foundation | ☐ |
| No foundation | ☐ |
| Deep foundation | Reinforced-concrete bearing
piles | ☐ |
Reinforced-concrete skin
friction piles | ☐ |
| Steel bearing piles | ☐ |
| Steel skin friction piles | ☐ |
| Wood piles | ☐ |
| Cast-in-place concrete piers | ☐ |
| Caissons | ☐ |
| Other | Described below | ☐ |
4. Socio-Economic Aspects4.1 Number of Housing Units and Inhabitants
Each building typically has less than 10 housing unit(s). Not applicable as these were used as public space.
Each dome-roof provides cover to one large platform at ground level. The number of inhabitants in a building during the day or business hours is more than 20 persons. The number of inhabitants during the evening and night is 5-10 persons. These buildings had been uses as public buildings so the number of inhabitants depended upon the population area it served.
4.2 Patterns of Occupancy
Public places, for small to large population.
4.3 Economic Level of Inhabitants
| Income class | Most appropriate type |
| a) very low-income class (very poor) | ☐ |
| b) low-income class (poor) | ☐ |
| c) middle-income class | ☑ |
| d) high-income class (rich) | ☑ |
Economic Level:
The ratio of price of housing unit to the annual income can be 1:1 for middle class families.
| Ratio of housing unit price to annual income | Most appropriate type |
| 5:1 or worse | ☐ |
| 4:1 | ☐ |
| 3:1 | ☐ |
| 1:1 or better | ☑ |
What is a typical source of
financing for buildings of this
type? | Most appropriate type |
| Owner financed | ☐ |
| Personal savings | ☑ |
Informal network: friends and
relatives | ☐ |
Small lending institutions / micro-
finance institutions | ☐ |
| Commercial banks/mortgages | ☐ |
| Employers | ☐ |
| Investment pools | ☐ |
| Government-owned housing | ☐ |
| Combination (explain below) | ☐ |
| other (explain below) | ☑ |
Governors from taxes. Or people of an area gathered and built -for example- a public bath or mosque. In each housing unit, there are no bathroom(s) without toilet(s), no toilet(s) only and no bathroom(s) including toilet(s).
Usually no bathroom provided. .
4.4 Ownership
The type of ownership or occupancy is outright ownership, ownership by a group or pool of persons and others.
Type of ownership or
occupancy? | Most appropriate type |
| Renting | ☐ |
| outright ownership | ☑ |
Ownership with debt (mortgage
or other) | ☐ |
| Individual ownership | ☐ |
Ownership by a group or pool of
persons | ☑ |
| Long-term lease | ☐ |
| other (explain below) | ☑ |
It is public building owned by the governor or people of the area.
5. Seismic Vulnerability5.1 Structural and Architectural Features
Structural/
Architectural
Feature | Statement | Most appropriate type |
| True | False | N/A |
| Lateral load path | The 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. | ☑ | ☐ | ☐ |
Building
Configuration | The building is regular with regards to both the plan
and the elevation. | ☑ | ☐ | ☐ |
| Roof construction | The 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. | ☑ | ☐ | ☐ |
| Floor construction | The 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. | ☑ | ☐ | ☐ |
Foundation
performance | There is no evidence of excessive foundation movement
(e.g. settlement) that would affect the integrity or
performance of the structure in an earthquake. | ☑ | ☐ | ☐ |
Wall and frame
structures-
redundancy | The number of lines of walls or frames in each principal
direction is greater than or equal to 2. | ☑ | ☐ | ☐ |
| Wall proportions | Height-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); | ☑ | ☐ | ☐ |
Foundation-wall
connection | Vertical load-bearing elements (columns, walls)
are attached to the foundations; concrete
columns and walls are doweled into the
foundation. | ☐ | ☑ | ☐ |
Wall-roof
connections | Exterior walls are anchored for out-of-plane seismic
effects at each diaphragm level with metal anchors or
straps | ☐ | ☐ | ☑ |
| Wall openings | 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. | ☐ | ☑ | ☐ |
| Quality of building materials | Quality of building materials is considered to be
adequate per the requirements of national codes and
standards (an estimate). | ☐ | ☑ | ☐ |
| Quality of workmanship | Quality of workmanship (based on visual inspection of
few typical buildings) is considered to be good (per
local construction standards). | ☑ | ☐ | ☐ |
| Maintenance | Buildings of this type are generally well maintained and there
are no visible signs of deterioration of building
elements (concrete, steel, timber) | ☐ | ☑ | ☐ |
| Other | | ☑ | ☐ | ☐ |
5.2 Seismic Features
| Structural Element | Seismic Deficiency | Earthquake Resilient Features | Earthquake Damage Patterns |
| Wall | N/A | N/A | N/A |
| Frame (columns, beams) | Constructed of low strength brittle materials, the structural elements are unreinforced. | well defined load path, high rigidity | diagonal cracks more often in mortar, shear and tensile failure at the column bottom |
| Roof and floors | Constructed of low strength brittle materials, heavy in weight, the roof is unreinforced, opening in the roof, large span | well defined load path, perfect distribution of forces and stresses | No significant damage except that caused by column failure |
| Other | No second seismic system like tie beams | NA | Crushing of brick material |
This type of structure has continuous load path like concrete columns with concrete shell connecting the columns at the top, except that bricks and mortars do not have that material properties.
5.3 Overall Seismic Vulnerability Rating
The overall rating of the seismic vulnerability of the housing type is B: MEDIUM-HIGH (i.e., poor seismic performance), the lower bound (i.e., the worst possible) is A: HIGH (i.e., very poor seismic performance), and the upper bound (i.e., the best possible) is C: MEDIUM (i.e., moderate seismic performance).
| Vulnerability | high | medium-high | medium | medium-low | low | very low |
| | very poor | poor | moderate | good | very good | excellent |
Vulnerability
Class | A | B | C | D | E | F |
| ☐ | ☐ | ☐ | ☐ | ☐ | ☐ |
5.4 History of Past Earthquakes
| Date | Epicenter, region | Magnitude | Max. Intensity |
| 2003 | Bam | 6.5 | VIII |
As stated above this type has been constructed thousands years ago, hence there must have been many other earthquakes especially the historical ones that affected these buildings. However, information in not available.
6. Construction6.1 Building Materials
| Structural element | Building material | Characteristic strength | Mix proportions/dimensions | Comments |
| Walls | Brick & adobe | 40-120 kg/cm2 | 20x10x10 – 50x50x20 cm | Varies from places and ages |
| Foundation | Brick & stone | 40 – 150 kg/cm2 | Not much bigger than the walls | Varies from places and ages |
| Frames (beams & columns) | NA | | | |
| Roof and floor(s) | Brick & adobe | 40 – 120 kg/cm2 | 20x10x10 – 50x50x20 cm | Varies from places and ages |
6.2 Builder
As stated earlier, this type was usually built for public uses. May be in the past, the labors lived in the building temporarily who built it.
6.3 Construction Process, Problems and Phasing
Experienced persons, master builders and may be some contractors with help of labors built the structure, with shovel, hack, float and other old construction equipment. The construction of this type of housing takes place incrementally over time. Typically, the building is originally designed for its final constructed size.
6.4 Design and Construction Expertise
There were no academically qualified engineers or architects and no standard codes for design of this type of building structures were available. These might have been constructed by empiricism or experimentation. However, it is still a issue of research. There are no academically qualified engineers or architects for this type of buildings.
6.5 Building Codes and Standards
This construction type is not addressed by the codes/standards of the country.
NA.
6.6 Building Permits and Development Control Rules
This type of construction is not an informal, and not authorized as per development control rules.
This is a historic building typology and is not anymore being constructed nowadays, except for creating the past architecture of Persia. Building permits are not required to build this housing type.
6.7 Building Maintenance
Typically, the building of this housing type is maintained by Builder, Owner(s) and others. sometimes the governor maintains the building.
6.8 Construction Economics
Approximately US$70-80 /m2. 5-15 persons for about 6-12 month depending on the size of the building.
7. Insurance
Earthquake insurance for this construction type is typically available. For seismically strengthened existing buildings or new buildings incorporating seismically resilient features, an insurance premium discount or more complete coverage is not available. Earthquake insurance is included in fire insurance and it’s based on the value of the building. 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 of the governors’ properties. So these.
8. Strengthening
8.1 Description of Seismic Strengthening Provisions
Strengthening of Existing Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| No shear wall | add a shear wall to the system by filling between the arches. |
| Damages in load path (columns) | 1. add a shear wall to the system by filling between the arches. 2. embed some materials to maintain the column. |
| opening in roof | Strengthening all around the opening. |
| heavy weight | Remove the heavy weight materials of the roof and replace them with light new materials. |
| large span | Constructing some horizontal tie beams (timber, cable or steel bar). |
| Unreinforced arch | Reinforcing of the arch by prestressed with cable or steel bar at spring level |
The construction materials used in these buildings do not comply with the Iranian codes.
8.2 Seismic Strengthening Adopted
Has seismic strengthening described in the above table been performed in design and construction practice, and if so, to what extent?
No.
Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake?
They are used for both issues.
8.3 Construction and Performance of Seismic Strengthening
Was the construction inspected in the same manner as the new construction?
No.
Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineer involved?
Government.
What was the performance of retrofitted buildings of this type in subsequent earthquakes?
NA.
Reference(s)- History of engineering in Iran
Farshad,M.
Balkh Publications 1997
- Iranian retrofitting provision for existing buildings : Section 7 - Masonry structures and infills
IIEES
- Iran insurance co., http://www.iraninsurance.ir
- Earthquake Engineering Theory and Applications
Moghaddam,H.
Farahang Publication 2002
- Siamak Ahi webblog, http://chaartaagh.blogspot.com/
Author(s)- Nima T. Bekloo, NA
No.24 St.18 velenjak ave.TehranIran, Tehran 1985743337, IRAN
Email:poosad@gmail.com FAX: (9821)-22171696
Reviewer(s)
