| Report # | 104 |
| Report Date | 25-02-2004 |
| Country | IRAN |
| Housing Type | Adobe / Earthen House |
| Housing Sub-Type | Adobe / Earthen House : Mud walls with horizontal wood elements |
|
Author(s)
|
Mehrdad Mehrain, Farzad Naeim |
|
Reviewer(s)
|
Marcial Blondet |
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 type is typically one or two stories and used for single-family housing. It is more predominant in the desert, in cold-weather, or other inhospitable climates. It has a large mass
and basically no strength, particularly against out-of-plane wall forces. These buildings are the most seismically vulnerable. In the 2003 Bam earthquake, collapse of these buildings was widespread and contributed to many of the 43,000+ deaths. The typical mode of collapse is out-of-plane failure of the walls, resulting in loss of support for the roof. Adobe construction is widespread throughout Iran, and is used both by wealthy families in luxury residences, as well as by poor families in more modest dwellings.
1. General Information
Buildings of this construction type can be found in Middle East. This type of housing construction is commonly found in both rural and urban areas. This construction type has been in practice for less than 100 years.
Currently, this type of construction is being built. Adobe construction is widespread throughout Iran, and is used both by wealthy families in luxury residences as well as poor families in more modest dwellings.
Figure 1: Modest adobe house
| 
Figure 2: View of adobe construction with multiple domes | 
Figure 3: Luxury adobe house
|
|
2. Architectural Aspects2.1 Siting
These buildings are typically found in flat terrain. They share common walls with adjacent buildings. The typical separation distance between buildings is more than one meter, if not connected to adjacent buildings
2.2 Building Configuration
It is rectangular in plan. Small windows, one entrance door and one entry for each room. Opening area is about 30 percent of total wall area.
2.3 Functional Planning
The main function of this building typology is single-family house. These buildings can also be found in steep hillside areas, where an individual house is on a flat foundation, but then steps into another house's roof. In a typical building of this type, there are no elevators and no fire-protected exit staircases. There is only one door to exit from the building.
2.4 Modification to Building
No modifications are made to the building.
Figure 4: Historic adobe structure
| 
Figure 5: Section of luxury adobe house.
| 
Figure 6: Ceiling skylight in wealthy adobe dwelling |
Figure 7: Entryway in wealthy adobe home
|
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) | ☐ |
3.2 Gravity Load-Resisting System
The vertical load-resisting system is earthen walls. The roofs are usually adobe domes or cylindrical arches, supported on adobe walls. Sometimes flat adobe roofs with wood joists are used (as described in section 2, if these buildings are built on hillsides, the ground floor of one building can be the roof for another.).
3.3 Lateral Load-Resisting System
The lateral load-resisting system is earthen walls. The lateral load-resisting elements are adobe walls, typically 3 m high, 4 m wide and 0.80 m thick. The walls do not have any additional system (such as crown beam or pilasters) to restrain their out-of-plane movement. That is one reason why the buildings are so vulnerable in earthquakes. If the walls move out of plane, the roof loses its support, and collapses.
3.4 Building Dimensions
The typical plan dimensions of these buildings are: lengths between 12 and 12 meters, and widths between 12 and 12 meters. The building is 1 storey high. The typical span of the roofing/flooring system is 4 meters. Typical Plan Dimensions: the dimensions can vary, but typically modest homes are 12 meters by 12 meters. Large homes can be very extensive.
Typical Number of Stories: typically, these adobe houses are only one story high.
Typical Span: a cylindrical or dome-shaped arched roof typically spans 4 meters. More elaborate buildings will have such a vaulted ceiling in the center, flanked by semi-spherical rooms that have domes spanning 3 to 4 meters. A poorer owner may have one cyclindrical ceiling. The typical storey height in such buildings is 3 meters. The typical structural wall density is more than 20 %. The typical structural wall density varies from 10% to 35%.
The walls are very thick, typically
+/- 70-80 cm.
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 roofs (and walls) typically have a 5 cm (2 inch) layer of straw reinforced mud to provide protection against rain.
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 | ☐ |
Figure 8: Perspective of a typical modest adobe dwelling. Cylindrical roof goes over rectangular center space,
domes are used for the square rooms. |
4. Socio-Economic Aspects4.1 Number of Housing Units and Inhabitants
Each building typically has 1 housing unit(s). There is only one unit in each building. 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.
4.2 Patterns of Occupancy
Just one family, possibly with married son anddaughter-in-law, lives in each unit.
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) | ☐ |
The ratio of price of each housing unit to the annual income can be 10:1 for very poor and poor families, and 20:1 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) | ☐ |
In each housing unit, there are no bathroom(s) without toilet(s), no toilet(s) only and no bathroom(s) including toilet(s).
Bathrooms or latrines are in separate structures. .
4.4 Ownership
The type of ownership or occupancy is outright ownership and ownership with debt (mortgage or other).
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) | ☐ |
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 | They are weak in the out of plane direction. | There are no earthquake resistant features. | The walls tips over or bend outwards. |
| Frame (Columns, beams) | | | |
| Roof and floors | It is made of weak materials. | The roof consists of arches and domes which provide integrity | If the walls move out of plane, the roof collapses. |
| Other | | | |
if the adobe walls can be kept in place, the seismic performance of the building will improve significantly.
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 |
| 1990 | Manjil | 7.7 | |
| 1997 | Ardekul | 7.3 | |
| 2003 | Bam | 6.6 | |
Iran has a long history of devastating earthquakes that have affected adobe structures. In the 2003 Bam earthquake, over 40,000 people died; in 1997 over 1,568 people died and in the 1990 earthquake in Manjil over 40,000 people died. In the Bam area, there have also been other significant earthquakes: in the Gisk-Zarand 1977 earthquake--665 people were killed; in the 1981 Golbaf earthquake--betwen 1,000 and 3,000 people were killed; in the 1981 Sirch earthquake--1300 people killed. Many people were killed in adobe structures.
Figure 9: Key Seismic Deficiency--buildings not well-tied together. Example of building collapse in Bam earthquake | 
Figure 10: Aerial view of roofs after Bam earthquake--multiple domes of each house are visible. | 
Figure 11: Key Seismic Deficiency: walls are not tied to roof, and can move out-of-plane in an earthquake |
Figure 12: Aerial view of complete destruction of adobe dwelllings in Bam earthquake | 
Figure 13: Aerial view of neighborhood with widespread damage to adobe structures in Bam earthquake | 
Figure 14: If walls can be kept in-plane, building typically survives. Adobe house in Bam earthquake. |
Figure 15: Bam earthquake: Damage to a traditional adobe house. Nonbearing walls collapsed, bearing walls are
still standing. | 
Figure 16: Bam earthquake: collapsed adobe structures | 
Figure 17: Bam earthquake: debris cleared from roadway, partially collapsed adobe structures, tents |
|
6. Construction6.1 Building Materials
| Structural element | Building material | Characteristic strength | Mix proportions/dimensions | Comments |
| Walls | Adobe is used to make walls. | No information is available on this. | No information is available on this. | |
| Foundation | | | | |
| Frames (beams & columns) | | | | |
| Roof and floor(s) | Adobe is used to make walls. | No information is available on this. | No information is available on this. | |
6.2 Builder
Builder Occupied.
6.3 Construction Process, Problems and Phasing
Sun dried adobe units are used to build walls and roof. A 2-inch layer of straw-reinforced mud covers the walls and roof for rain protection. Every 4 to 6 years, this layer is washed away from the roof and requires replacement. 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
No special expertise. None.
6.5 Building Codes and Standards
This construction type is not addressed by the codes/standards of the country.
6.6 Building Permits and Development Control Rules
This type of construction is a non-engineered, and not authorized as per development control rules. Building permits are not required to build this housing type.
6.7 Building Maintenance
Typically, the building of this housing type is maintained by Owner(s).
6.8 Construction Economics
$20/m2 (this is a rough estimate. A lot of people build their own houses, using their own dirt to make adobe blocks.). It takes about 100 days for 2-3 persons (200-300 person days) to complete the construction.
7. Insurance
Earthquake insurance for this construction type is typically unavailable. For seismically strengthened existing buildings or new buildings incorporating seismically resilient features, an insurance premium discount or more complete coverage is unavailable.
8. Strengthening
8.1 Description of Seismic Strengthening Provisions
Strengthening of Existing Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Weak walls | In other countries, particularly Peru, add reinforced concrete, or add rope stitching |
Strengthening of New Construction :
| Seismic Deficiency | Description of Seismic Strengthening provisions used |
| Weak walls | Dimensional constraints, bamboo reinforcement (Peru) or reinforced concrete overlay. |
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?
None in Iran.
Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake?
Not applicable.
8.3 Construction and Performance of Seismic Strengthening
Was the construction inspected in the same manner as the new construction?
Not applicable.
Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineer involved?
Not applicable.
What was the performance of retrofitted buildings of this type in subsequent earthquakes?
Not applicable.
Figure 18: Basic gravity strengthening technique used for several hundred years--iron rod across vaulted space,
tying walls together (increases gravity resistance, not seismic resistance) |
Reference(s)
Author(s)- Mehrdad Mehrain
Vice-President, URS Corporation
911 Wilshire Blvd., Los Angeles CA 90017, USA
Email:Michael_Mehrain@URSCorp.com FAX: (213) 996-2375
- Farzad Naeim
Vice President, John A. Martin & Associates
1212 South Flower Street 4th Floor, Los Angeles CA 90015, USA
Email:farzad@johnmartin.com FAX: (213) 483-3084
Reviewer(s)- Marcial Blondet
Professor
Civil Engineering Dept., Catholic University of Peru
Lima 32 , PERU
Email:mblondet@pucp.edu.pe FAX: 51-1-463-6181
