Report #: 75

Report Date:

Country: ALGERIA

Housing Type:

Housing Sub-Type:

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

Last Updated:

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: 101-200 years

Still Practiced: No

In practice as of: 1950

Building Occupancy: Mixed residential/commercial

Typical number of stories: 5

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments:

This construction was practiced prior to 1950 by French contractors.It is the same construction type found in countries around

Plan Shape: Square, solidSquare, with an opening in planRectangular, solidRectangular, with an opening in planL-shapeTriangular, with an opening in planE-shapeU- or C-shapeIrregular plan shape

Additional comments on 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)

Typical plan length (meters): 25

Typical plan width (meters): 15

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: 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.

Gravity load-bearing & lateral load-resisting systems: The predominant structural system is composed of load bearing external stone masonry walls and wooden floors slabs. Thick external walls are distributed in both directions, however interior non-structural walls are thin and used to partitioning the space. In some cases, varied structural units (adobe, brick and stone) and systems are used resulting in variable wall strength and stiffness. Photos 03 & 04

Typical wall densities in direction 1: 5-10%

Typical wall densities in direction 2: 5-10%

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.Openings are categorized according to their construction period and method; in some of them wooden lintels are used and in others the top of the opening is closed with a small vault.

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 footingShallow Foundation: Rubble stone, fieldstone strip footing

Additional comments on foundation:

Type of Floor System: Other floor system

Additional comments on floor system: Floor: vaulted masonry (bricks) supported by steel beams Floor and roof structures are not considered as rigid diaphragms.

Type of Roof System: Roof system, other

Additional comments on roof system: Timber: wood planks or beams that support clay tiles Floor and roof structures are not considered as rigid diaphragms.Photo 03

Additional comments section 2: Typical separation distance between buildings: 4-6 meters

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.

Who typically builds this construction type?: Other

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

Is this construction type address by codes/standards?: No

Applicable codes or standards:

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

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 type of construction is permitted in seismic areas if resisting elements are added as extra strength reinforced concrete ties in vertical and horizontal directions.

Typical problems associated with this type of construction:

Who typically maintains buildings of this type?: Other

Additional comments on maintenance and building condition: Problems with maintenance - most of this construction is in a lamentable state.

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

Labor requirements: Information not available.

Additional comments section 3:

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

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: 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

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

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

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.

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.

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