Report #: 159

Report Date:

Country: PAKISTAN

Housing Type:

Housing Sub-Type:

Author(s): Yasir Irfan Badrashi, Qaisar Ali, Mohammad Ashraf

Last Updated:

Regions Where Found: It is estimated that reinforced concrete buildings constitute 10 to 15% of the total building stock in the major cities of Pakistan and this percentage is on the rise.

Summary: This report addresses reinforced-concrete buildings in Pakistan. Due to the rapid urbanization in Pakistan in the recent past and consequently the scarcity and inflated cost of land in the major cities, builders have been forced to resort to the construction of reinforced-concrete buildings both for commercial and residential purposes. It is estimated that reinforcedconcrete buildings constitute 10 to 15% of the total building stock in the major cities of Pakistan and this percentage is on the rise. However, construction of reinforced concrete buildings in Pakistan is still in nascent stage with construction procedures lacking compliance with the established construction procedures. This report is based on survey of the building stock of 5 major cities in Pakistan and hence provides a realistic picture of construction of reinforced-concrete buildings in Pakistan. The statistics provided in this report are based on personal observation of the authors as well as opinion of professionals working in the construction industry who were interviewed in the course of this survey.

Length of time practiced: Less than 25 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Mixed residential/commercialOther

Typical number of stories: 3-8

Terrain-Flat: Typically

Terrain-Sloped: 4

Comments:

Buildings of this construction type can be found in the urban areas of the major cities being the hub of this kind of constructi

Plan Shape: Rectangular, solid

Additional comments on plan shape: Reinforced-concrete structures are usually rectangular in plan. However, in certain cases other planar profiles such as L, T, U or even curved profiles can also be found in larger buildings like plazas and hotels, aesthetics being the main motivation in adopting irregular shapes. In elevation, these buildings usually have a regular configuration; however, in some cases the difference in stiffness in different stories may cause soft story effect. In privately owned buildings, the trend has been to allocate the ground and first floors to commercial facilities like shops while the upper stories are used as residential dwellings in form of apartments. In order to increase the floor area, these apartments are projected outwards thus causing disproportion between the inter story stiffness. A typical building plan, elevation and picture of construction are given in Figure 1, 2 and 3, respectively.

Typical plan length (meters): 10-40

Typical plan width (meters): 10-20

Typical story height (meters): 3

Type of Structural System: Structural Concrete: Moment Resisting Frame: Designed with seismic effects, with URM infill walls

Additional comments on structural system: The vertical load-resisting system is reinforced concrete moment resisting frame. Gravity loads are resisted purely by the reinforced-concrete frame. The typical load transfer path is from the slabs to beams to columns and finally to the footings of the building.

The lateral load-resisting system is reinforced concrete moment resisting frame. Different lateral load resisting systems are provided by structural designers in the reinforced-concrete buildings in Pakistan. Reinforced-concrete frames usually are either OMRF or IMRF. Very important buildings have SMRF configuration as well as in some cases dual systems are encountered, too. Reinforced-concrete frames usually have brick or block masonry infill walls which help contribute to the lateral load-resisting system.

Gravity load-bearing & lateral load-resisting systems: Reinforced-concrete buildings prior to the Kashmir 2005 earthquake were mostly designed for gravity loading only. However, after the Kashmir 2005 earthquake, a reasonable importance is being given to consideration of earthquake induced loading in the design of these buildings. Reinforced-concrete buildings in Pakistan at present are generally designed as moment-resisting frames, however, a particular building-resisting system would depend largely on the budget allocated to the project and to some extent on the importance of the building. Low- to mid-rise buildings are generally OMRF, while taller buildings with a higher importance level, are designed as SMRF or dual systems (moment-resisting frame with shear walls).

Typical wall densities in direction 1: 0-1%

Typical wall densities in direction 2: 0-1%

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

Wall Openings: In residential facilities each room is normally provided with one or two doors and one or two windows. Doors are usually located near the corners of the rooms with sizes in the range of 3.0 square meters and are usually wooden, but in some instances aluminum doors are constructed nowadays owing to their durability as compared to wooden doors. Windows are provided in the walls with sizes of 2.0 to 2.25 square meters. Reinforced-concrete lintels are provided above the openings in the brick masonry infills. These lintels are connected to the columns by dowel bars in case of good quality construction but in ordinary construction, this feature is missing. When reinforced-concrete buildings are used to house commercial facilities, openings may be lesser and differently located as compared to the ones in residential units though the sizes of the openings are almost the same. Infills in concrete frames may be of different material for commercial buildings, usually glass infills for decorative purposes which are provided generally in the front walls. Such type of individual commercial units usually have one door and no openings.

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

Modifications of buildings: When modified, reinforced-concrete buildings are modified at times without permission of the governing authority that is responsible for the construction in a particular area and in some instances the builder may get away with it, too. The most common modifications performed on the building are relocation of the masonry infill walls to suit the needs of the residents. In some cases, brick masonry infill walls are replaced with wooden boards as partition walls. Other modifications include the construction of additional stories as well as the confinement of the terraces to increase living space. The addition of stories that are not considered in the design of the building can lead to catastrophes.

Type of Foundation: Shallow Foundation: Reinforced concrete isolated footingShallow Foundation: Reinforced concrete strip footingShallow Foundation: Mat foundationDeep Foundation: Reinforced concrete skin friction piles

Additional comments on foundation: It consists of reinforced concrete skin-friction piles. Foundations for low- to mid-rise reinforced-concrete buildings are usually isolated column footings with size in the range of 1.5 square meters with thickness of about 0.15 meters. A layer of lean concrete is usually provided beneath the footing to act as a cushion against the soil effects. At times combined footings are also provided when loads are higher for low- to mid-rise buildings. In larger structures and heavy loadings, raft foundations are preferred in recent construction practice. In high-rise buildings, taller than 20 stories, deep foundations are also provided consisting of usually skin-friction piles.

Type of Floor System: Other floor system

Additional comments on floor system: Solid Slabs (Cast-in-Place) Flat Slabs (Cast-in-Place) Other: Floors/roofs are generally constructed in reinforced concrete and are monolithic with the load-resisting system (beams). Usually the thickness of roof slabs is 0.13 to 0.15 meters. Slabs are supported on their edges by beams which are cast monolithical with reinforced-concrete slabs.

Type of Roof System: Roof system, other

Additional comments on roof system: Floors/roofs are generally constructed in reinforced concrete and are monolithic with the load-resisting system (beams). Usually the thickness of roof slabs is 0.13 to 0.15 meters. Slabs are supported on their edges by beams which are cast monolithical with reinforced-concrete slabs.

Additional comments section 2: Since the major cities of Pakistan are located on flat terrain, it can be safely said that reinforced-concrete frame structures are most commonly found in flat areas. However, after the October 2005 earthquake and the reconstruction following in its wake, reinforced-concrete buildings are constructed in the hilly areas of Abbottabad and Mansehra, too, but their proportion in the total building stock is much less (not more than 1 to 2% of the total building stock) as compared to the major cities. Small residential buildings located in densely populated areas of cities do not have an appreciable distance between them but larger buildings do have a distance from 3 to 10 meters between them.

Who is involved with the design process?: EngineerArchitect

Roles of those involved in the design process: Since a lot of capital is involved in the construction of reinforced-concrete buildings, the owners hire the services of architects and structural engineers to carry out the architectural and structural design of the buildings. The role of engineers and architects for designing and construction of a reinforced-concrete building in Pakistan vary from project to project and from city to city. For projects of importance, it has been a usual practice to hire services of an architect for carrying out the architectural design while a structural designer would further design the agreed architecture of the building.

Expertise of those involved in the design process: The expertise of these professionals varies from city to city in Pakistan. If a project is of high importance, architects and structural engineers from other developed cities may also be employed for carrying out the designs.

Who typically builds this construction type?: MasonOther

Roles of those involved in the building process: Regarding execution of the construction activities, in good projects, the contractor may hire services of a site engineer or a group of engineers for supervising the construction activities, their number dependent on the spectrum of the project. In construction, there may be or may not be site engineers hired for supervising the construction.

Expertise of those involved in building process: Masons, steel fixers and other skilled workers rely solely on their experience gained over the years and are seldom trained professionally.

Construction process and phasing: Construction process of reinforced concrete buildings may be different for public and privately owned buildings. In case of public buildings, owned by government of Pakistan, the concerned line department both designs and supervise the construction itself or it may hire services of a private consulting agency to carry out the design and supervise the execution of construction activities. In case of privately owned reinforced concrete buildings, several possibilities have been observed. The owners may hire the services of an architect for carrying out the architectural design of the building. Architects would further hire services of a structural engineer to carry out the structural design. Usually execution of construction is carried out through a contractor who may either charge the owner through a BOQ (Bill of Quantities) or carry out the construction by providing with skilled workmen while the materials are supplied either by a third party or arranged by the owners themselves. The former procedure amongst the two is more common. The construction sequence involves the leveling of the work site, excavation of the foundation pits, pouring of lean concrete (1:4:8 or 1:8:16), placement of the formwork and tying of the reinforcing bars and finally pouring of concrete. This is further followed up by the construction of the stub columns and plinth beams (in some cases) and the construction of the columns. Beams are cast in place after the construction of the columns making sure that there is enough embedment of the column reinforcement into the beams. RCC slab follows the construction of the beams. Brick masonry infill walls are constructed after laying of the roof slab and finally plastering and other finishing works are carried out. The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size. In well-planned construction, it is usually ensured that the actual construction would comply to the designed plans and structural configurations as provided by the design office. However, in some cases, the builders/owners may change the configuration of the building themselves. The usual changes incorporated in this way are covering up open spaces to increase living area, relocation of infill walls etc.

Construction issues

Is this construction type address by codes/standards?: Yes

Applicable codes or standards: This construction type is addressed by the codes/standards of the country. Building Code of Pakistan governs the design and construction of reinforced-concrete buildings in Pakistan. The year the first code/standard addressing this type of construction issued was 2007. Building code of Pakistan 2007 (BCP 2007) is the code that is followed for design of reinforced-concrete buildings. However, since BCP 2007 is essentially UBC 97 except for seismic zonation that has been carried out indigenously, in true essence these buildings are designed in accordance with design specifications of UBC 97. The specifications usually referred to regarding materials are ASTM specifications which govern the quality assurance of steel, concrete, bricks etc. The most recent code/standard addressing this construction type issued was 2007. Building Code of Pakistan is typically used to design and construct these buildings.

Process for building code enforcement: Ideally the design and construction of reinforced concrete buildings should be governed by the building code of Pakistan. Every city has a building control authority that authorizes the construction after evaluating it. However this evaluation in most cases is limited to verification of the proposed design in light of the local building by-laws. In buildings of high importance, there has been a growing trend in the major cities of Karachi and Lahore to vet the structural designs too, though this practice is not common in the other cities. In government owned buildings, construction is either supervised by the nominated consultants or by the government organization itself which somehow ensures construction according to approved designs and specifications. On the other side, construction of reinforced concrete buildings owned privately, there usually is no supervision of construction quality by a building code enforcing agency. Summarizing it, it may be stated that designs are usually compliant to the building code of Pakistan while quality of construction vary and may not conform to the standard specifications.

Are building permits required?: Yes

Is this typically informal construction?: No

Is this construction typically authorized as per development control rules?: Yes

Additional comments on building permits and development control rules: Since reinforced-concrete buildings are mostly constructed in the urban areas of Pakistan which usually has a building control authority that governs the construction of buildings in that particular city. Therefore building permits are required to execute construction of these buildings.

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: Typically, the building of this housing type is maintained by Owner(s) and Tenant(s). Since these buildings are either sold to individual owners or rented out to tenants, maintenance of these buildings is carried out by either of these.

Unit construction cost: Unit construction cost of reinforced concrete buildings in Pakistan is highly variable. The cost varies according to the location of the building to the amount of facilities provided in the building.

Labor requirements: 10-15 persons working 8 hours a day can complete an approximately 280 square meter building in four months.

Additional comments section 3:

Damage patterns observed in past earthquakes for this construction type: A low to moderate seismic activity has been active in many parts of Pakistan, especially in the Northwestern province, though the other parts of Pakistan had also experienced mild to severe intensity earthquakes in the past. In 1936, the earthquake with a magnitude of 8.1 on the Richter scale, that hit the capital of the Balochistan province, Quetta, resulted in a very high death toll (around 30,000 killed). But the usual seismic activity occurs in the northwestern part of Pakistan with the epicenter in range of 250 kilometers from the provincial metropolis, Peshawar. According to MSK, Peshawar may be placed in intensity zone VI or at most in VII, Islamabad in VI, and Lahore in V. In October 2005, a strong earthquake hit the upper northern parts of the NWFP province causing severe damage to buildings and resulted in loss of lives in the tune of 70,000.

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 frames: Inadequate seismic design, sub-standard concrete quality, disparity between the specified design and actual layout of reinforcement, deficiency in the provision of clear cover in concrete, vertical alignment of columns is sometimes not ensured.

Strong beam-weak column failures are the most common. In October 2005 Muzaffarabad earthquake, main failure was due to the formation of the plastic hinges just below the beam-column connection and at the base of the column.

Earthquake-resilient features in frame: Due to high redundancy, multiple load paths are available for efficient resistance of seismic forces, masonry infill w alls contribute to the lateral resisting system.

Seismic deficiency in roof and floors: Failure of the roof slabs and floors were not noticed in the Muzaffarabad 2005 earthquake. The roof slabs that failed were due to the additional demand that was a result of the failure of the adjoining frame elements.

Earthquake resilient features in roof and floors: The usual thickness of the roof slabs is 125 to 150 mm. These slabs have high stiffness and thus efficiently transfer the seismic loads to the concrete frames they are connected to.

Seismic deficiency in foundation: Seismic design of the isolated column footing is not usually considered. Though rarely any foundation failure were observed in the October 2005 Muzaffarabad earthquake.

As such no damage of the foundations was observed in reinforced concrete structures during the past earthquakes in Pakistan.

Earthquake-resilient features in foundation: In some cases, plinth beams are provided to connect the individual spread footings. This practice results in a more efficient seismic performance of the RC frames.

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

Additional comments section 5: The overall rating of the seismic vulnerability of the housing type is C: MEDIUM VULNERABILITY (i.e., moderate seismic performance), the lower bound (i.e., the worst possible) is B: MEDIUM-HIGH VULNERABILITY (i.e., poor seismic performance), and the upper bound (i.e., the best possible) is D: MEDIUM-LOW VULNERABILITY (i.e., good seismic performance).

During the past earthquakes, especially the Kashmir 2005 earthquake, almost all types of construction were heavily damaged. Mostly damaged was the load-bearing brick masonry structures and stone masonry residential buildings. Reinforced-concrete buildings failed too in many places, especially the worst hit areas of Abbottabad and Mansehra and even in the national capital, Islamabad. Deficiency in the construction materials (concrete, improper placement of the reinforcement etc.) and strong beam-weak column phenomena were the main reasons for the failure of the RC frame structures. These local failures caused global instability in the structural system. Typical damage patterns of reinforced concrete are given in Figures 4, 5 and 6.

Additional comments on seismic strengthening provisions: Seismic strengthening is usually carried out in accordance with the Building Code of Pakistan.

Has seismic strengthening described in the above table been performed?: Pakistan has been struck by many earthquakes ranging from mild to high intensities but there have been no records of the damages incurred by the buildings. The practice of retrofitting or strengthening has not been prevalent in Pakistan. People prefer to raze down the buildings and reconstruct them. This can be attributed to lack of research and absence of skilled engineers working in the field of seismic retrofitting and strengthening. However, in recent times, especially in the areas severely affected by the 2005 earthquake, several projects have been carried out to retrofit schools and hospital buildings, but on a larger scale usually no retrofitting is carried out.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?: This work was carried out as a repair work after the Kashmir 2005 earthquake.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?: Strengthening was carried out by structural engineers from Earthquake Engineering Centre, University of Engineering & Technology, Peshawar

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?: There has been no earthquake of appreciable damage potential since this work was carried out to assess the performance of the strengthened building.

A critical review of the seismic risk zoning and development of design spectra for Peshawar and adjoining areas Qaisar Ali and Akhtar Naeem Khan 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada 2004

Seismic performance study of brick masonry building systems in Peshawar region Qaisar Ali

Observed Seismic Behavior of Buildings in Northern Pakistan During the 2005 Kashmir Earthquake Amjad Naseer, Akhtar Naeem Khan, Zakir Hussain, and Qaisar Ali Earthquake Spectra 2010 26