Unreinforced concrete and masonry bearing wall construction (designed for gravity loads only), Palestinian Territories

From World Housing Encyclopedia


1. General Information

Report: 49

Building Type: Unreinforced concrete and masonry bearing wall construction (designed for gravity loads only)

Country: PALESTINIAN TERRITORIES

Author(s): Jalal N. Al Dabbeek, Abdel H. W. Al-Jawhari

Last Updated:

Regions Where Found: Buildings of this construction type can be found in the main cities of West Bank like East of Jerusalem, Nablus, Ramallah, Bethlehem and Jenin. It represents 20 to 30% of the housing stock in these cities. For Gaza Strip, it was applied on a small scale because the stone blocks needed were not available there. This type of housing construction is commonly found in both rural and urban areas.

Summary: This building type is usually found in most cities of the West Bank and less often in the Gaza Strip. It is a traditional, non-engineered, low-rise construction practice. The main lateral load-resisting system consists of bearing walls with unreinforced concrete strip foundation. The interior masonry walls consist of plain concrete (system #2) or two wythe stone masonry walls filled with plain concrete (system #1). The exterior bearing walls consist of stone masonry facing with a plain concrete backup. Wall thickness ranges from 400 to 500 mm (system #1) to 300-mm thickness in system #2. It is important to note that system #1 represents the old practice for bearing-wall construction while system #2 represents the new trend which was developed and used from the 1950s to the 1970s. This construction is not practiced at the present time.

Length of time practiced: 76-100 years

Still Practiced: No

In practice as of:

Building Occupancy: Residential, 3-4 unitsMixed residential/commercial

Typical number of stories: 2

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments: The main function of this building typology is mixed use (both commercial and residential use).


2. Features

Plan Shape: Rectangular, solid

Additional comments on plan shape:

Typical plan length (meters): 20

Typical plan width (meters): 20

Typical story height (meters): 41734

Type of Structural System: Masonry: Stone Masonry Walls: Massive stone masonry (in lime/cement mortar)

Additional comments on structural system: The vertical and lateral load bearing systems are the same. These walls transfer the vertical loads to the foundations. The foundations typically consist of spread footings of plain concrete with stone boulders resting on stiff soil or rock. The lateral load resisting system consists of bearing walls resting on unreinforced concrete strip foundation. These masonry walls consist of plain concrete with or without stone. They are very thick (40-50 cm) and of high density. Thus the building weight is very high, and it generates high inertia forces during earthquake. The walls are not connected properly to the foundation, to the floor slabs and to each other. The buildings are generally regular and have only minor variation in stiffness between different floors, except the irregularity due to some variations or changes in the stiffness of the internal walls. The initial stiffness of these walls is not a reliable measure of its strength since it degrades very quickly after the first earthquake shock. This is especially true for the buildings having more than two stories (see Figures 11, 12 and 13).

Gravity load-bearing & lateral load-resisting systems: The selection of the type of structural system represents system #1, whereas system #2 can be classified as masonry concrete with stone covering for the external walls and without for the internal walls.

Typical wall densities in direction 1: 10-15%

Typical wall densities in direction 2: 10-15%

Additional comments on typical wall densities: 10% - 15% total wall area/plan area (for each floor) is the range between the ratios of the area of all the walls in each principal direction divided by the total area of the plan.

Wall Openings: The windows and doors are usually centered within the wall. The height of the windows usually varies from 1.8 to 2.0 meters, and the width has a variable size depending on the architect's experience and personal judgment. Generally, the windows represent 10 to 20% of the wall area. The doors are 1.2 to 1.5 meters wide and 2.2 to 2.5 meters high as an average.

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

Modifications of buildings: Investigations on this type of buildings showed the following: - Some changes in the size and location of the openings are made especially in the internal walls. - Extensions to buildings are applied in many cases using either short, medium or long time intervals. - Staircases are added whenever additional floors are needed. This happens in very few cases where staircases do not exist in single floor buildings. - When adding additional floors, the bearing wall system is usually changed according to the new function, architectural and structural system adopted.

Type of Foundation: Shallow Foundation: Rubble stone, fieldstone strip footing

Additional comments on foundation:

Type of Floor System: Other floor system

Additional comments on floor system: (cast-in-place) reinforced-concrete slabs resting on steel girders (see Figure 10). (cast-in-place) reinforced-concrete slabs resting on steel girders (see Figure 10).

Type of Roof System: Roof system, other

Additional comments on roof system: (cast-in-place) reinforced-concrete slabs resting on steel girders (see Figure 10). (cast-in-place) reinforced-concrete slabs resting on steel girders (see Figure 10).

Additional comments section 2: Typical Plan Dimensions: Length and width are varied from 10 to 20 meters. Typical Story Height: Typical story height is 4 - 5 meters. Typical Span: Usually typical span ranges from 4 to 6 meter. The typical storey height in such buildings is 5 meters. The distance between adjacent buildings varies from 6 to 10 meters in the areas classified for housing purposes and zero for commercial areas


3. Building Process

Description of Building Materials

Structural Element Building Material (s) Comment (s)
Wall/Frame Wall: Concrete bearing wall (internal) Concrete/Stone (external) Wall: Characteristic Strength - 1.0-2.0/15-20 /1.0- 2.0 1.0-2.0/15- 20/1.0-2.0 Mix proportions - 1:3:6 - 1:3:5 Comments - The stone used for decorative purposes in the external walls is neglected in the strength (Represents system 2 only since system1 was not governed by identified parameters)
Foundations Concrete Characteristic Strength - 1-2/15-20/1-2 Mix proportions - 1:3:6 Comments - (Represents system 2 since system 1 was not governed by identified parameters).
Floors Concrete Characteristic Strength - 1-2/15-20/1-2 Mix proportions - 1:3:6 Comments - (Represents system 2 since system 1 was not governed by identified parameters).
Roof Concrete Characteristic Strength - 1-2/15-20/1-2 Mix proportions - 1:3:6 Comments - (Represents system 2 since system 1 was not governed by identified parameters).
Other

Design Process

Who is involved with the design process? Other

Roles of those involved in the design process: For system 1, no engineers were available except for very few number of draftsmen or authorized designers. The engineers association was not there. For system 2, very few engineers were available and the engineers association was just started. In both cases, the personal experience of the workmen and the conventional methods governed the process. As mentioned above, the engineers played only a limited role especially in preparing the drawings for system

Expertise of those involved in the design process:


Construction Process

Who typically builds this construction type? Owner

Roles of those involved in the building process: The builder lives in this type in many cases. Also, a developer sometimes built the house for investment purposes and others bought or rented it.

Expertise of those involved in building process: The major role during the construction process was played by the contractors and local builders.

Construction process and phasing: The construction process can be briefly described as follows: (1) For system 1 : - A draftsman or a licensed engineer (very rarely) made the drawings for the building. The drawings followed only the traditional forms used by people at that time. Sometimes the owners with the help of the local builders made their own houses without preparing drawings by specialized people. - Many of the buildings had the same design concerning heights, dimensions, openings, and sometimes number and distribution of rooms and spaces. - The drawings which usually included only architectural design without any detailing were signed by the designer mentioned above and submitted to the municipality or the authorized departments for building license. - A contractor or a builder was assigned by the owner to build the house without using any procurement process. - The work was not usually done under the supervision of the engineers who were not available. - Generally, traditional building methods ere applied and all the work was done manually using traditional tools and depending on the personal experience of the builders. - The time of construction used to be very long and sometimes lasted for years. (2) For system 2 - The architectural and structural drawings were prepared by the engineer (usually the same) without preparing the necessary detailing. - The drawings were signed by the authorized engineer and submitted to the municipality for building license - No electrical or mechanical design was made. This was usually applied on site and during construction by skilled labors who used only their personal experience and conventional methods. - The work was awarded by the owner to local contractors or builders. Procurement methods were rarely applied.. - More effective building techniques were applied but still conventional and also the personal experience of the contractor or builder governed the process. - The time of construction as a result was relatively long but less than that for system 1 - So e of the buildings were built under the supervision of engineers. The construction of this type of housing takes place incrementally over time. Typically, the building is originally not designed for its final constructed size.

Construction issues:


Building Codes and Standards

Is this construction type address by codes/standards? No

Applicable codes or standards:

Process for building code enforcement: There was no national code for this type of construction. Also no specified court of law was applied to ensure good quality construction.


Building Permits and Development Control Rules

Are building permits required? Yes

Is this typically informal construction? No

Is this construction typically authorized as per development control rules? No

Additional comments on building permits and development control rules:


Building Maintenance and Condition

Typical problems associated with this type of construction:

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

Additional comments on maintenance and building condition:


Construction Economics

Unit construction cost: These housing systems are not used anymore. To build a housing unit of this type or even to buy it, the cost is more than 50000 $US. The estimated cost at the time of construction (during the 1950s) is around 2000 $US (This does not include the land price which was generally cheap at that time).

Labor requirements: For a housing unit of system 1 nearly 1500 workdays or person days were required to complete the construction and for system 2 the number was 1000 workdays.

Additional comments section 3:


4. Socio-Economic Issues

Patterns of occupancy: One family generally occupies one housing unit. We can find in very few cases or even rarely more than one family in one housing unit. Each building typically has multiple housing units. Ground floor can be used for commercial purposes. Each building typically has 4 housing unit(s). The number of housing units in the type considered in this study (as Figure 1) varies between 2-4. In few cases, especially in Nablus and Ramallah cities, the number of the units may reach up to 8 units in each building.

Number of inhabitants in a typical building of this construction type during the day: 5-10

Number of inhabitants in a typical building of this construction type during the evening/night: 10-20

Additional comments on number of inhabitants:

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

Additional comments on economic level of inhabitants: These figures represent the present cost. The cost of construction was much lower when these building were constructed. Economic Level: For Poor Class the Housing Unit Price is 40,000 and Annual Income is 5,000. For Middle Class the Housing Unit Price is 40,000 and the Annual Income is 9,000. Ratio of housing unit price to annual income: 5:1 or worse

Typical Source of Financing: Owner financedPersonal savings

Additional comments on financing:

Type of Ownership: RentOwn outrightOwned by group or pool

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: No

What does earthquake insurance typically cover/cost:

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
1927 Jericho MMI,VII
1995 Aqaba Gulf MMI, VII - VIII

Past Earthquakes

Damage patterns observed in past earthquakes for this construction type: - The magnitude of the Aqaba Gulf earthquake ranged between 6.2-6.5. -The magnitude of the Jerico earthquake ranged between 6.2-6.3. - In the 1995 earthquake, the Epicenter was located about 100 kilometers south of Aqaba and Elat cities where MMI was VII.

Additional comments on earthquake damage patterns:


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. FALSE
Building Configuration-Vertical The building is regular with regards to the elevation. (Specify in 5.4.1) TRUE
Building Configuration-Horizontal The building is regular with regards to the plan. (Specify in 5.4.2) TRUE
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. TRUE
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. TRUE
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. FALSE
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). N/A
Quality of Workmanship Quality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards). TRUE
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: Interconnection of different components: foundation, walls, roof slabs is poor.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: #NAME?

Earthquake-resilient features in walls:

Seismic deficiency in frames:

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors: #NAME?

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation: The footings are not well connected to achieve the necessary stiffness

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
A B C D E F
Seismic vulnerability class |- o -|

Additional comments section 5:


6. Retrofit Information

Description of Seismic Strengthening Provisions

Structural Deficiency Seismic Strengthening

Additional comments on seismic strengthening provisions: The retrofitting of these structures is not described in any provisions. It is performed rarely by individual engineers without applying unique principles and tools. In general, jacketing using reinforced concrete or steel is used for strengthening purposes.

Has seismic strengthening described in the above table been performed? Information not available.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?

Was the construction inspected in the same manner as new construction?

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?

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

Additional comments section 6:


7. References

  • Building Construction Under Seismic Conditions in the Balkan Region, Volume 3 (Design and Construction of Stone and Masonry Buildings) UNDP/UNIDO - Project RER/79/015, 1984, Vienna 1984
  • Building code requirements for structural concrete and commentary, ACI 318-95 American Concrete Institute (ACI) 1995
  • Vulnerability and seismic performance of buildings in Palestine Al-Dabbeek,J. Expert Meeting on Earthquake Engineering and retrofit, UNESCO, Beirut 2000
  • 1999 and 2000 Bulletins and site investigation reports Earth Sciences and Seismic Engineering Center (ESSEC), An-Najah University, Palestine 1999-2000
  • European Microseismic Scale (EMS) Luxembourg 1998
  • The Aqaba earthquake of November 22, 1995 Hussein Malkawi,A.I, Numayr,K.S., and King,S.A. Earthquake Spectra, 15 (3), 397-415 1999
  • Seismic risk assessment and design of building structures Koridze,A. Omega Scientific, UK 1988
  • Drawings of Wahid and Ala'Din Al-Jawhari buildings Municipality of Nablus-Engineering Department, Building License Section 1935, Nablus Palestine Nablus Palesti 1960
  • Learning from earthquake-the Aqaba earthquake of November 22, 1995 Osman,A. and Ghobarah,A. EERI Special Earthquake Report, May 1995

Authors

Name Title Affiliation Location Email
Jalal N. Al Dabbeek Civil Engineer/Associate Professor Center of Earth Sciences & Seismic Engineering, An-Najah National University P.O. Box 707, Nablus West Bank , PALESTINIAN TERRITORIES seiscen@najah.edu
Abdel H. W. Al-Jawhari Civil Engineer Engineering Department, Municipality of Nablus P.O. Box 218, Nablus , PALESTINIAN TERRITORIES awjawhari@nablus.org

Reviewers

Name Title Affiliation Location Email
Ravi Sinha Professor Civil Engineering Department, Indian Institute of Technology Bombay Mumbai 400 076, INDIA rsinha@civil.iitb.ac.in
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