Stone masonry apartment building, Algeria

From World Housing Encyclopedia

1. General Information

Report: 75

Building Type: Stone masonry apartment building

Country: Algeria

Author(s): Mohammed Farsi, Farah Lazzali, Yamina Ait-Mziane

Last Updated: 6/17/2003

Regions Where Found: These stone masonry buildings exist throughout northern Algeria. In particular, the multi-story buildings exist mainly in the major cities e.g. Algiers, Oran, Constantine, Annaba, etc. This construction type may constitute 40 to 50% of the urban housing stock.

Summary: Stone masonry building is typical multy-family residential construction found in most Algerian urban centres, and it constitutes 40 to 50% of the total urban housing stock. This construction, mostly built before 1950s by French contractors, is no longer practiced. Buildings of this type are typically 4 to 6 stories high. The slabs are wooden structures or shallow arches supported by steel beams (jack arch system). Stone masonry walls, usually 400 to 600 mm thick, have adequate gravity load-bearing capacity, however their lateral load resistance is very low. As a result, these buildings are considered to be highly vulnerable to seismic effects.

Length of time practiced: Less than 200 years

Still Practiced: No

In practice as of: Prior to 1950.

Building Occupancy: Mixed residential/commercial

Typical number of stories: 5

Are buildings of this type typically built on flat or sloped terrain?: Both

Comments: This construction was practiced prior to 1950 by French contractors. This type of construction is found in the older urban districts.

2. Features

Plan Shape: The building plan for this housing type can be of different forms: rectangular, L-shaped, U-shaped, etc. (see photos 1 and 2).

Additional comments on plan shape: None

Typical plan length (meters): 25

Typical plan width (meters): 25

Typical story height (meters): 3.5

Type of Structural System: Masonry: Stone Masonry Walls: Rubble stone (field stone) in mud/lime mortar or without mortar (usually with timber roof). Masonry: Stone Masonry Walls: Massive stone masonry (in lime/cement mortar)

Additional comments on structural system: None

Gravity load-bearing & lateral load-resisting systems: Lateral load-resisting system: The lateral load-resisting system consists of the stone masonry walls built in longitudinal and cross directions. Wall thickness varies from 400 to 600 mm. Low-strength mortar (either cement/sand or mud mortar) has been used. According to the Algerian Seismic Code (RPA99), this construction is permitted only if confined with reinforced concrete ties in vertical and horizontal direction, and with RC slabs used as floor and roof structures. The maximum building height allowed by the Code depends on the seismic zone (17 m, 14 m and 11 m, for seismic zones I, II and III, respectively). Gravity load-bearing system: Stone masonry walls are the principal elements of the gravity load-bearing structure.

Typical wall densities in direction 1: 5% - 6%

Typical wall densities in direction 2: 5% - 6%

Additional comments on typical wall densities: The ratio of total wall area/plan area (for each floor) in each principal direction is between 5% and 6%.

Wall Openings: The number, size and position of openings for a typical floor in a building are shown on the typical plan (Figure 3). The total window and door area is about 25% of the overall wall surface area.

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

Modifications of buildings: Modifications are often undertaken by the residents without any professional assistance provided by engineers. They include demolition of interior walls, opening commercial areas, and vertical extensions.

Type of Foundation: Shallow Foundation: Wall or column embedded in soil, without footing. Shallow Foundation: Rubble stone (fieldstone) strip footing

Additional comments on foundation:

Type of Floor System: Masonry: Vaulted. Masonry: Masonry and steel jack arch structure.

Additional comments on floor system: Floor and roof structures are not considered as rigid diaphragms.

Type of Roof System: Timber: wood planks or beams that support clay tiles.

Additional comments on roof system: Floor and roof structures are not considered as rigid diaphragms. Photo 03

Additional comments section 2: Typical separation distance between buildings is 5 meters.

3. Building Process

Description of Building Materials

Structural Element Building Material (s) Comment (s)
Wall/Frame Wall: Field stone in cement or mud mortar Massive stones used at the corners and around the openings
Foundations Field stone in cement or mud mortar
Floors Vaulted bricks
Roof Vaulted bricks

Design Process

Who is involved with the design process? Architect

Roles of those involved in the design process: Only architects had a role in the design/construction of this housing type

Expertise of those involved in the design process: The level of expertise of all parties involved in the design and construction process was at the worldwide level of the 20th Century.

Construction Process

Who typically builds this construction type? Architect

Roles of those involved in the building process: Owners and contractors were involved in the construction of this type. This construction was practiced prior to 1950 by French contractors.

Expertise of those involved in building process: The level of expertise of all parties involved in the design and construction process was at the worldwide level of the 20th Century.

Construction process and phasing: The stone blocks were laid by hand and the basic construction equipment was used. This building type was typically constructed incrementally and so was not always designed for its final constructed size.

Construction issues: N/A

Building Codes and Standards

Is this construction type address by codes/standards? No

Applicable codes or standards: None

Process for building code enforcement: Not applicable - building codes are not applicable to this construction practice.This construction type was used before the advent of seismic codes

Building Permits and Development Control Rules

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: Permits are now required for public buildings for the vertical extensions, structural interventions and for repair and strengthening.

Building Maintenance and Condition

Typical problems associated with this type of construction: Problems with maintenance - most of this construction is in a lamentable state.

Who typically maintains buildings of this type? Owner(s); Renter(s).

Additional comments on maintenance and building condition: None

Construction Economics

Unit construction cost: 10 000-15 000 Algerian Dinars /m.sq. (150-200 $US/sq.m.)

Labor requirements: Information not available.

Additional comments section 3: None

4. Socio-Economic Issues

Patterns of occupancy: In Algeria there is a serious housing crisis. On an average, there are two families occupying the same housing unit: the parents and a son's or daughter's family.

Number of inhabitants in a typical building of this construction type during the day: 44105

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

Additional comments on number of inhabitants: In most cases the women in the families are not working and stay at home during the day.

Economic level of inhabitants: Low-income class (poor)

Additional comments on economic level of inhabitants: Economic Level: For the Poor Class the ratio of Housing Price Unit to their Annual Income is 10:1.

Typical Source of Financing: Owner financedPersonal savingsGovernment-owned housing

Additional comments on financing:

Type of Ownership: RentOwn outright

Additional comments on ownership:

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

What does earthquake insurance typically cover/cost: Earthquake insurance for all construction types is available since 2004 This insurance, known as CATNAT, was set up following the Boumerdes earthquake by the group of insurance companies. The insurance premium is assessed, for the moment, only on the seismic zone, the surface and the height of the construction. Since the begining of 2013, a working group was set up to reflect on the parameters to be taken into account for the evaluation of the premium

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: No

Additional comments on premium discounts:

Additional comments section 4:

5. Earthquakes

Past Earthquakes in the country which affected buildings of this type

Year Earthquake Epicenter Richter Magnitude Maximum Intensity
1980 El-Asnam 7.3 X (MMI)
1989 Tipaza 6.2 VIII-IX (MSK)
1994 Mascara 5.6 VIII (MSK)
1999 Ain-Tmouchent 5.8 VIII (MSK)
2003 Boumerdes 6.8 IX-X (MMI)

Past Earthquakes

Damage patterns observed in past earthquakes for this construction type: Damage patterns vary from diagonal “X”-cracks to total wall collapse, and partial to total collapse of the roofs/slabs.The following damage patterns were also observed:- Horizontal cracks between walls and floors, - Vertical cracks at walls intersections, - Out of plane collapse of external walls, - Diagonal cracks in wall piers, - Partial or complete disintegration of walls, - Partial or complete collapse of the building

Additional comments on earthquake damage patterns: Earthquake Total Number of Apartment Buildings (all types) Damage level (MSK scale) 1 2 3 4 5 1980 El-Asnam 4844439 1304 1351 863 8871989 Tipaza 4511 1480 1102 223 426 12801994 Mascara 1874 470 302 351 212 5391999 Ain-Tmouchent 3398 1062 606 684 528 518

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 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. TRUE
Building Configuration-Vertical The building is regular with regards to the elevation. (Specify in 5.4.1) FALSE
Building Configuration-Horizontal The building is regular with regards to the plan. (Specify in 5.4.2) FALSE
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. FALSE
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. FALSE
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. TRUE
Wall and Frame Structures-Redundancy The number of lines of walls or frames in each principal direction is greater than or equal to 2. TRUE
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); TRUE
Foundation-Wall Connection Vertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation. TRUE
Wall-Roof Connections Exterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. FALSE
Wall Openings TRUE
Quality of Building Materials Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). FALSE
Quality of Workmanship Quality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards). FALSE
Maintenance Buildings 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 some cases, the use of these buildings changed.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: - Poor mortar strength;- Walls not tied together;- varied structural units (adobe, brick and stone) and systems

Earthquake-resilient features in walls:

Seismic deficiency in frames:

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors: -Not monolithic;-Not rigid in-plane;

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:

Seismic Vulnerability Rating

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

High vulnerabilty Medium vulnerability Low vulnerability
Seismic vulnerability class o

Additional comments section 5: Behavior of masonry buildings when subjected to seismic event is depending on how the walls and the floors are interconnected and anchored. In the majority of observed masonry buildings where the timber joist is not anchored to the masonry, walls tend to separate along their intersections causing vertical cracks.

6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening
Cracks in the stone masonry walls - Cracks less than 0.3 mm width; by injection using fluid cement mortar- Large cracks: injection and adding stitching dog or steel bars; rebuilt using bricks or stones to bridge the crack zone in case of vertical crack; using metallic plate in case
Lack of integrity Addition of horizontal and vertical RC ties at exterior and steel ties in the interior, see Figure 7A

Additional comments on seismic strengthening provisions:

Has seismic strengthening described in the above table been performed? These strengthening techniques were used to repair and strengthen the damaged buildings after the Algerian earthquakes reported in this contribution. A guide for using these seismic strengthening techniques is available in Algeria (“Mthodes de Rparation et de Renforcement des Ouvrages” was edited by CGS in 1992).

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Vulnerability studies for strategic buildings were done in 1996 at Algiers City, and some buildings of this type were strengthened as a result of the study.

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? A contractor performed the construction and engineers were involved.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? Good.

Additional comments section 6:

7. References

  • Benedetti D., Benzoni G., Parisi M.A. (1988). Seismic Vulnerability and Risk Evaluation for Old Urban Nuclei, Earthquake Engineering and Structural Dynamics, Vol. 16, 183-201.
  • Boutin, C., E. Ibraim, et S. Hans (1999). Auscultation de Btiments Rels en Vue de l'Estimation de la Vulnrabilit, Vme Colloque National PS “Gnie Parasismique et Rponse Dynamique des Ouvrages”, ENS 3- 3- Cachan, 1, 298-305.
  • C. Boutin, S. Hans, E. Ibraim (2000). Pour une approche exprimentale de la vulnrabilit sismique, Revue franaise de gnie civil, vol 4 (6), pp. 682-714.
  • Coburn A.W., Spence R.J.S., Pomonis A. (1992). Factors Determining Casuality Levels in Earthquakes: Mortality Prediction in Building Collapse, 10th WCEE, Madrid, Spain.
  • Centre National de Recherche Applique en Gnie Parasismique (2000), Rgles Parasismiques Algriennes (RPA99), Alger, Algrie
  • Cochrane S.W., Schaad W.H. (1992). Assessment of Earthquake Vulnerability of Buildings, 10 WCEE, Madrid, Spain.
  • European Seismological Commission (1993). European Macroseismic Scale 1992, Grnthal G. Editor, Luxembourg.
  • Farsi M. N., Belazougui M. (1992). The Mont Chenoua (Algeria) earthquake of October 29th, 1989: Damage assessment and distribution, 10WCEE, Madrid, Spain.
  • Farsi M. N. (1996). Identification des Structures de Gnie Civil Partir de Leurs Rponses Vibratoires et Vulnrabilit du Bti Existant. Thse de Doctorat, Observatoire de Grenoble, LGIT, Universit Joseph Fourier.
  • Karnik V., Schenkova Z., Schenk V. (1984). Vulnerability and the MSK Scale, Engineering Geology, 20, 161-168.
  • Petrini V. (1995). Overview Report on Vulnerability Assessment, 5th ICSZ, Nice, France
  • Spence R.J.S., Coburn A.W., Pomonis A. (1992). Correlation of Ground Motion with Building Damage: The Definition of a New Damage-Based Seismic Intensity Scale, 10 WCEE, Madrid, Spain.
  • Tebbal F. (1985). Estimation Prliminaire du Risqu Sismique dans la Ville d'Alger, CTC.
  • Office National des Statistiques (ONS), recensement gnral de l'habitat et de la population, Algiers, 1998
  • M. Benblidia, J. R. Liu, Y. M. Xu, M. N. Farsi, M. Slimani & A.A. Chaker (1986). Etude de Vulnrabilit de la Ville de Djelfa, ANAT.
  • CGS (1992). “Mthodes de Rparation et de Renforcement des Ouvrages”, Algeria.


Name Title Affiliation Location Email
Mohammed Farsi Head of Department CGS Kaddour Rahim St, BP 252, HUSSEIN-DEY, Algiers 16040 Algeria,
Farah Lazzali Researcher CGS Kaddour Rahim St, BP 252, HUSSEIN-DEY, Algiers 16040 Algeria
Yamina Ait-Mziane Researcher CGS Kaddour Rahim St, BP 252, HUSSEIN-DEY, Algiers 16040 Algeria


Name Title Affiliation Location Email
Marjana Lutman Research Engineer Slovenian National Building & Civil Engineering Ljubljana 1000, SLOVENIA
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