| Report # | 118 |
| Report Date | 26-05-2007 |
| Country | IRAN |
| Housing Type | Unreinforced Masonry Building |
| Housing Sub-Type | Unreinforced Masonry Building : Brick masonry in mud/lime mortar |
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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
This building structure derives its name from the four earrings that are constructed at the four corners of a rectangular building at the spring level of dome roof. This structural system was developed due to the lack of of wood and stone. It was widely constructed more than 3 thousand years ago, after the invention of the dome-roof structures in the Old Persian Empire (Ashkanian & Sasanian). The main problem with the dome-roof building was to transform the rectangular or polygonal plan of the group of walls into the circular plan at the spring level of dome roof. They used to construct the first row of dome and then construct another row on top of previous one with a little offset closer to the center of the dome circle and so on. That was too difficult to construct. This system was invented to resolve this problem. In this system, once the walls were constructed, four earrings (shekanj) built upon four corners of walls intersections, and then it was much easier to build a dome over these. It is an ideal system to resist vertical and gravity loads and transform them into horizontal and shear loads. For lateral loads, domes behave like trusses and distribute the load to the other parts of the structure creating a perfect load path.
1. General Information
Buildings of this construction type can be found in throughout the Persian Empire, except places near the sea. This type of housing construction is commonly found in both rural and urban areas.
This building type is more common in old and traditional cities.
This construction type has been in practice for less than 100 years.
Currently, this type of construction is being built. This construction system is, now-a-days, rarely constructed. These are mostly constructed in areas of low population density in the middle of the desert (Kavir) or in small towns where construction materials such as steel, cement are not abundantly available.
Figure 1: Typical Building
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Figure 2: Key Load-Bearing Elements
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Figure 3: Key Load-Bearing Elements
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Figure 4: Plan of a Typical Building
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Figure 5: Critical structural details
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Figure 6: Critical structural details
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Figure 7: Critical structural details
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Figure 8: Critical structural details
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Figure 9: Critical structural details
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Figure 10: Critical structural details
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Figure 11: Key seismic feature
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Figure 12: Typical earthquake damage
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Figure 13: Typical earthquake damage
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Figure 14: Typical earthquake damage
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Figure 15: Illustration of seismic strengthening technique |
Figure 16: Inside view of the earring
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Figure 17: Soltanieh dome, Zanjan, IRAN (this dome was built without earring) | 
Figure 18: Earring over polygonal section (Kerman, IRAN) |
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2. Architectural Aspects2.1 Siting
These buildings are typically found in flat terrain. They share common walls with adjacent buildings. Most of the time, this building type sits in a group without any separation distance between them
2.2 Building Configuration
Building configuration in plan is often rectangular or octagonal, or sometimes even polygon with more arms. Due to its load bearing system, it does not have many openings. The openings are usually less than 30% of wall area. Sometimes openings are also provided in the roof as well. These are usually around 50 cm in diameter.
2.3 Functional Planning
The main function of this building typology is single-family house. Sometimes (especially in the old times) the whole family (including relatives) lived in a large rectangular with one common entrance. They might have used same courtyard, kitchen and service, but slept in separate rooms. One kind of these building type was known as four Eyvan (Balcony). In a typical building of this type, there are no elevators and no fire-protected exit staircases. Usually there was only one exit in this building type.
2.4 Modification to Building
Because the structural system is the load bearing system, it is possible only to modify some small openings.
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) | ☐ |
1. Sometimes walls and dome of the buildings constructed with mud mixed with pebbles as well.
2. Nowadays some people use cement based mortar as well.
3.2 Gravity Load-Resisting System
The vertical load-resisting system is earthen walls. Load bearing walls and dome-roof system.
3.3 Lateral Load-Resisting System
The lateral load-resisting system is earthen walls. Load bearing walls and dome-roof system.
3.4 Building Dimensions
The typical plan dimensions of these buildings are: lengths between 5 and 20 meters, and widths between 5 and 20 meters. The building has 1 to 2 storey(s). The typical span of the roofing/flooring system is 5-20 meters. Typical Plan Dimensions: The typical plan dimension depend on the building function (residential, barn, mosque etc). The dimensions may vary, but over all the structure have a regular plan shape.
Typical Story Height: The storey height depends on the building function (residential, barn, mosque etc).
Typical Span: Single span for the single roof. The typical storey height in such buildings is 4-20 meters. The typical structural wall density is more than 20 %. 20% to 40%.
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. By building it in vault form, the forces are distributed on the 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 | ☐ |
NA.
4. Socio-Economic Aspects4.1 Number of Housing Units and Inhabitants
Each building typically has 1 housing unit(s). One unit in each building.
One large room is covered by one dome-roof. The number of inhabitants in a building during the day or business hours is less than 5. The number of inhabitants during the evening and night is less than 5. NA.
4.2 Patterns of Occupancy
Houses of this type are mostly occupied by a single family.
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) | ☐ |
Nowadays very small number of people live in this type of building.
Economic Level:
The ratio of price of housing unit to the annual income can be 1:1 for poor 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) | ☐ |
NA. In each housing unit, there are 1 bathroom(s) without toilet(s), 1 toilet(s) only and no bathroom(s) including toilet(s).
As stated in section 2.4 when the whole family lived together, they shared the same bathroom and latrine. .
4.4 Ownership
The type of ownership or occupancy is renting and outright ownership.
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) | ☐ |
NA.
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 | Constructed of low strength brittle materials, the structural elements are unreinforced, walls are large and heavy | Well defined load path, high rigidity, continues bearing (Shear) walls | Vertical and diagonal cracks in walls, more often along mortar joints |
| Frame (columns, beams) | NA | NA | NA |
| Roof and floors | Constructed of low strength brittle materials, heavy in weight, the roof is unreinforced, opening in the roof, slipping of the roof over walls large span, | well defined load path, perfect distribution of forces and stresses | No significant damage except that caused by wall damage especially when walls under the dome slip leaving the dome roof without any support |
| Other | Not enough distance between adjacent buildings, no second seismic system like tie beams, | NA | Crushable brick material, weak mortar band |
This type of structure has continuous load path like concrete shear walls with concrete shell at top that connects the walls However, present building is constructed of extremely weak and brittle materials. Once cracked, the materials start crumbling.
5.3 Overall Seismic Vulnerability Rating
The overall rating of the seismic vulnerability of the housing type is A: HIGH VULNERABILITY (i.e., very poor seismic performance), the lower bound (i.e., the worst possible) is A: HIGH VULNERABILITY (i.e., very poor seismic performance), and the upper bound (i.e., the best possible) is A: HIGH VULNERABILITY (i.e., very poor 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 |
As stated above this type has been constructed thousands years ago, so there must be many other earthquakes especially historical ones that affected these buildings. However, no exact information is 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
Yes, the builder lives in the house. Traditionally every body has a co-operation in construction their own home.
6.3 Construction Process, Problems and Phasing
It is basically owner built construction where experienced persons, master builders and may be some local 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 in a single phase. 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 Standards for design of this type of building structures were available. These are 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 a non-engineered, and not authorized as per development control rules.
This type can only be seen in small villages and old towns nowadays. 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 and Owner(s). Often, the whole family work together for the maintenance of the building.
6.8 Construction Economics
Approximately US$ 80. For construction of an average size of house, 4-8 persons work for about 6 month.
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 available. Earthquake insurance is included in fire insurance and it’s based on the value of the building. It depends on the owner capital demand. usually for every US$ 5000 additional cover, it costs about US$ 6 /year added to the fire insurance.
8. Strengthening
8.1 Description of Seismic Strengthening Provisions
Strengthening of Existing Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Not enough distance between adjacent buildings | For buildings with different heights: 1.Destroy some common part of the adjacent walls to reach distance of 1% wall height. 2. Join all the buildings in an area to make them behave as a one single structure. |
| Damages in load path (exterior walls) | 1. Add a shear wall to the system. 2. Embed some materials to maintain the wall. 3. Filling the cracks by plaster, cement… |
| opening in roof | Strengthening all around the opening by wood or steel bars. |
| heavy weight | Remove the heavy weight materials of the roof and replace them with light new materials. |
| large span | Build some tie beams to make spans smaller. |
| Slipping the roof over the walls | Connect dome base with timber to prevent slipping. |
Iranian codes stated that they are not suitable for monuments.
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?
Both intervention options have been used. They are used for both matters.
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?
Owner, local masons without any no academic background in engineering.
What was the performance of retrofitted buildings of this type in subsequent earthquakes?
NA.
Reference(s)- History of engineering in Iran
Farshad,M.
Iranian code of practice for seismic resistant design of buildings Std.2800, BHRC 2005, Section 3 unreinforced masonry structures, Balkh Publication 1997
- Iran insurance co., http://www.iraninsurance.ir
- Iranian retrofitting provision for existing buildings, Section 7 masonry structures and infills
IIEES
- Iranian code of practice for seismic resistant design of buildings Std.2800, BHRC 2005, section 3 unreinforced masonry structures
- Earthquake Engineering Theory and Applications
Moghaddam,H.
Farahang Publication 2002
- Persians masters of empire
Researches group
Time Life Book Publication
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)
