Report #: 174

Report Date:

Country: PAKISTAN

Housing Type:

Housing Sub-Type:

Author(s): Sarosh Hashmat Lodi , Abdul Jabbar Sangi, Adam Abdullah

Last Updated:

Regions Where Found: Buildings of this construction type can be found in around 3.3% of all construction in Pakistan [1]. This type of construction is very popular in Karachi and its suburbs due to the ready availability of concrete blocks. Sand, gravel, aggregate, and cement, the necessary ingredients for casting concrete blocks, are conveniently available in Karachi. Cement is used as a binding agent, which gives the blocks their strength and durability (at the cost of adding substantial weight to the structure). In other parts of the country where sand and gravel are not available as easily it is more practicable to construct in brick, which is appropriate to those areas climatically as well as economically. Concrete block construction has also started to replace stone masonry in the northern areas of Pakistan because of its lower cost as compared to building in stone. In Karachi, concrete blocks are mass produced on a large scale and exported to the suburbs and outlying settlements bordering the central urbanized region. They have come to define the typical construction of Karachi. Concrete blocks are more commonly used as infill material within an RCC frame in most of the construction in Karachi. However, they can be used as load bearing members without reinforcement.

This type of housing construction is commonly found in both sub-urban and urban areas.

Summary: This report provides an overview of concrete block masonry housing construction, which is generally found in urban areas of Pakistan. Block masonry covers 3.3% of the total built environment of Pakistan. Block masonry construction is the most common type in less developed urban areas, where clay is not readily available, and ranges from one-storey houses to multi-storeyed buildings. The construction is generally carried out without any technical input. There are no guidelines and laws available to regulate it; therefore, it suffers from a number of weaknesses. This construction type is highly vulnerable to seismic forces.

Length of time practiced: 25-60 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Single dwellingMixed residential/commercial

Typical number of stories: 1-3

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments:

Concrete block construction has also started to replace stone masonry in the northern areas of Apart from being the main load

Plan Shape: Square, solidRectangular, solid

Additional comments on plan shape: As this type of construction is limited to urban or suburban regions where there are defined allotments of land rather than open parcels like in the countryside, buildings are strictly regular squares or rectangles in plan according to the plot size. Buildings contain basic living amenities. A main entrance door, which might not necessarily be located centrally on the external wall, opens into an interior lobby, from which one can access rooms or a staircase leading to an upper floor. Additional features like a wash basin, a water motor, and an underground tank may be located within this entrance lobby. Sometimes, the exterior door connects to an open veranda, and each interior room has its own door connected to the central veranda space. For other plots, shops may occupy the entire ground floor area, leaving just enough space for a minimal flight of stairs to the first floor where living facilities are provided.

Typical plan length (meters): 10-50

Typical plan width (meters): 5-30

Typical story height (meters): 2.5

Type of Structural System: Masonry: Unreinforced Masonry Walls: Concrete block masonry in cement mortar

Additional comments on structural system: The vertical load-resisting system is un-reinforced masonry walls. The loads from the roof are transferred to the walls and to the foundations. The lateral load-resisting system is un-reinforced masonry walls. The walls have a very low resistance to out of plane forces. In most cases, there is no proper connection between the roof and the walls.

Gravity load-bearing & lateral load-resisting systems:

Typical wall densities in direction 1: >20%

Typical wall densities in direction 2: >20%

Additional comments on typical wall densities: The typical structural wall density is unknown.

Wall Openings:

Is it typical for buildings of this type to have common walls with adjacent buildings?: Yes

Modifications of buildings: Smaller block masonry units are usually open to incremental modification as funds become available. These modifications can be in the form of ad hoc appendages to an existing, finished construction (Figure 5), or the addition of a single block masonry room or floor on top of an already built RCC ground floor (Figure 6). As block masonry construction is adopted by low and low-middle class residents, modifications to existing buildings are quite common, depending on when funds become available, and whether the owner decides to add more space to rent out to tenants as a source of additional income.

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

Additional comments on foundation: The foundations are block masonry wall footings laid in cement sand mortar, typically 1.5 to 2.5 feet deep, and 1.5 to 2.5 feet wide.

Type of Floor System: Composite cast-in-place reinforced concrete and masonry floor systemOther floor system

Additional comments on floor system: Structural concrete: Solid slabs (cast-in-place)

Type of Roof System: Roof system, other

Additional comments on roof system: Single story block masonry houses generally have a lighter roof made of steel girders with tiles or CGI sheets. Precast concrete beams and slab panels are also used in urban areas like Karachi. For block masonry buildings with 2 to 3 storeys, RC slab is also used. Single story block masonry houses generally have a lighter roof made of steel girders with tiles or CGI sheets. Precast concrete beams and slab panels are also used in urban areas like Karachi. For block masonry buildings with 2 to 3 storeys, RC slab is also used.

Additional comments section 2: These buildings can be found in the flattest of areas such as Karachi to quite rugged terrains such as the mountainous Gilgit and Hunza regions. The location of block masonry buildings depends more on the availability of suitable materials for construction than geographic features of the land. Another factor is the lack of availability of clay in the areas as they are located away from the river plains as shown in Figure 1. When separated from adjacent buildings, the typical distance from a neighboring building is 1-5 meters.

Who is involved with the design process?: None of the above

Roles of those involved in the design process: There are no design or construction guidelines available for this type of construction. Local masons rely on their past experience and the engineers or architects are not generally involved.

Expertise of those involved in the design process:

Who typically builds this construction type?: Owner

Roles of those involved in the building process: The builder is usually the owner of the house who decides whether to live in it or rent out portions as residential or commercial space.

Expertise of those involved in building process:

Construction process and phasing: Block masonry construction is usually carried out by local masons and labourers who rely on their experience. The foundations are generally constructed using block masonry with cement sand mortar and are wider than the walls. From plinth level, the walls are constructed in cement sand mortar. Various types of roofing materials are used which are generally directly resting on the walls without proper connections. 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

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

Applicable codes or standards:

Process for building code enforcement:

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:

Typical problems associated with this type of construction:

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

Additional comments on maintenance and building condition: Repairs consist largely of plaster peeling or blocks falling out of walls, which is not that common.

Unit construction cost: The cost of construction is roughly Rs. 7,500 to Rs. 10,000 per m2.

Labor requirements: The construction of a typical housing unit takes approximately 4 to 6 months to complete.

Additional comments section 3:

Damage patterns observed in past earthquakes for this construction type: The Indian plate upon which Pakistan, India and Nepal lie, is continuously moving northward and subducting under the Eurasian plate, thus triggering earthquakes in the process and forming the Himalayan mountains. Within the Suleiman, Hindu Kush and Karakoram mountain ranges, the Northern Areas, Chitral district in NWFP, Kashmir including Muzaffarabad, Quetta, Chaman, Sibi, Zhob, Khuzdar, Dalbandin, the Makran coast including Gwadar, and Pasni in Balochistan are located in high or very high risk areas. Cities of Islamabad, Karachi and Peshawar are located on the edges of high risk areas. Figure 7 shows the seismic zoning map of Pakistan, which was developed after 2005 Kashmir earthquake [2]. A large number of major earthquakes have hit Pakistan in 20th Century including: 1935 Quetta earthquake, 1945 Makran coast earthquake, 2001 Bhuj earthquake and 2005 Kashmir earthquake [3]. Figures 8 and 9 show the damage to block masonry houses in Kashmir 2005 earthquake.

Additional comments on earthquake damage patterns: Overall damage patterns observed in past earthquakes for this type of construction included : Collapse of wall due to out of plane effects and shear; Collapse of roof due to out of plane failure of walls.

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.

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: Poor lateral resistance, weak in out of plane direction, no lintel band, Improper opening proportions, poor quality of construction

Earthquake-resilient features in walls: There are no earthquake resistant features.

Seismic deficiency in frames: Heavy dead loads, no connection between roof elements and walls, lack of diaphragm action

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

Additional comments on seismic strengthening provisions: There are no specific set of provisions available for seismic strengthening and retrofitting of block masonry houses.

Seismic Vulnerability Assessment of Existing Buildings of Pakistan, Earthquake Model for Middle East Region (EMME) Lodi, S.H., N. Alam, and M. Ahmed (2012) Department of Civil Engineering, NED University of Engineering & Technology, Karachi, Pakistan

Building Code of Pakistan - Seismic Provisions Ministry of Housing & Works, Government of Pakistan

Seismic Hazard Analysis for the Cities of Islamabad and Rawalpindi Lindholm, C., et al. (2006) NORSAR and Pakistan Meteorological Department

Unreinforced Brick Masonry Residential Building Ali Qaisar (2006) World Housing Encyclopedia

First Report on the Kashmir Earthquake of October 8, 2005 Naeem, A., et al. (2005) EERI