Recent earthquakes in Pakistan demonstrated that the region is highlyseismic. Masonry buildings constructed with stones, concrete blocks, andfired-clay bricks and concrete buildings were damaged during the 8 October2005 Kashmir earthquake. This paper presents the seismic behavior ofreinforced concrete and masonry buildings in northern part of the North-WestFrontier Province (NWFP) and Kashmir during the earthquake. Most of thebuildings were observed to be nonengineered or semi-engineered. The paperpresents an overview of the 1937 Quetta building code and the 1986 and 2007building codes of Pakistan. Lessons learned during the earthquake are alsopresented. �DOI: 10.1193/1.3383119�
INTRODUCTION
On 8 October 2005, an earthquake of magnitude Mw=7.6 struck northeastern part ofthe North-West Frontier Province (NWFP) of Pakistan and southwestern part of Kashmir. Itcaused extensive damage to manmade infrastructure over an area of 30,000 sq. km in thedistricts of Manshera, Battagram, Abbottabad, and Shangla in NWFP, and Muzaffarabad,Bagh, Garhi Dubata, and Neelam in Azad Jamu and Kashmir (Figure 1). Balakot and Muzaf-farad were the worst-hit cities because of their proximity to the epicenter of the earthquake.Masonry buildings constructed with stones, concrete blocks, and fired-clay bricks and con-crete buildings were partially or severely damaged. The Kashmir earthquake resulted in morethan 73,000 casualties, while 80,000 people were injured, and more than 3 million peoplewere left homeless (ADB-WB 2005).
The Kashmir earthquake occurred on 8:50 a.m. local time (3:50 UTC). The epicenterwas estimated at 34.49° N and 73.63° E and located about 10 km �6.2 miles� NE ofMuzzaffarabad and 90 km north of Islamabad. The epicenter was estimated at a depth of26 km �16.2 miles� (USGS 2005). The direction of the fault was estimated to be fromN27E to N30E. The length of rupture was about 75 km �46.6 miles�. The fault plane dipsabout 29° and the mechanism is mostly thrust. The average slip was observed to be between2 to 5 meters (Bendick 2007, Jayangondaperumal and Thakur 2007).
a) NWFP University of Engineering & Technology, Peshawar, Pakistanb)
Balochistan University of Engineering & Technology, Khudzar, Pakistan
The main shock of the Kashmir earthquake and the epicentral area lie in theKashmir-Hazara syntaxis region, south of Himalaya (Jayangondaperumal and Thakur2007) as indicated in Figure 2. The surface trace of the fault extends from Balakot toMuzaffarabad and further SE for a length of 52 km �32.3 miles� (Jayangondaperumaland Thakur 2007).
In this paper, a brief overview of regional tectonic settings and seismicity is pro-vided. Seismic provisions of the country building codes of 1937, 1986, and 2007 arepresented. The performance of buildings during the Kashmir earthquake is discussed indetail. On the basis of the building code, the tectonic setting and seismicity of the re-gion, and lessons learned from the earthquake, conclusions are provided to mitigate haz-ards in the future. A brief discussion of the postearthquake research work is also pre-sented.
SEISMICITY OF THE REGION
Pakistan is situated in a region of high seismicity; two tectonic plates have theirboundaries in this region. The Indian plate, moving northward at a rate of about 30 mm�1.18 in.� per year, is subducting underneath the Eurasian plate, resulting in the high peaksof Himalaya, Karakoram, Pamir, Hindu-Kush and Tibetan Plateau. The northward compres-sive movement of Indian plate has also resulted in the multiple thrust faults (Figure 2) of the
Figure 1. Earthquake-affected areas within radii of 25 and 50 km from the epicenter (map showsthe cities of Muzaffarabad and Balakot, which were severely affected by the Kashmir earthquake,and Abbottabad, Murree and Nilore, where earthquake ground motions have been recorded.)
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 427
Eurasian Plate, which consequently cause many earthquakes in the region. The main bound-ary thrust (MBT), main mantle thrust (MMT), main Karakorum thrust (MKT) are examplesof thrust faults generated in this process.
Significant earthquakes that have occurred in the thrust zone are the 1555 Srinagarearthquake of Mw�6.7, 1897 Shilong earthquake of Mw=8, 1885 Kashmir earthquake ofMw=6.3, 1905 Kangra earthquake of Mw=7.8 (Bilham 2004), and 1974 Patten earthquake.The Shilong, Kangara, and Patten earthquakes resulted in the loss of 1,542, 20,000, and6,300 lives, respectively. The recent earthquake clearly demonstrates that the region has thepotential for producing major earthquakes. It is considered that only a small percentage ofthe stored energy in the active tectonic is released due to the Kashmir earthquake and is con-sidered moderate in the context of earthquake-generating potential of the region. There is apossibility for the repetition of earthquake of magnitude Mw�8 in the region affected by theKashmir earthquake (Avouac 2006).
Figure 2. Tectonic settings of the Kashmir earthquake. Major active faults are indicated in red.Dashed lines indicate approximate locations of the blind thrust faults. MBT: Main BoundaryThrust, MFT: Main Frontal Thrust, IKSZ: Indus-Kohistan Seismic Zone. (Courtesy of Jean-Philippe Avouac 2006)
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STRONG GROUND MOTION
The strong ground motion generated by the Kashmir earthquake was recorded atthree locations—Abbottabad, Murree and Nilore—by a network operated by PakistanAtomic Energy Commission under the Micro-Seismic Studies Program (MSSP). Theclosest instrument was located in Abbotabad, a city 52 km from epicenter. The instrumentis installed in a small room constructed on an alluvial deposit (Maqsood and Schwarz 2008).The components of the accelerogram of the main shock recorded at Abbottabad are repro-duced in Figure 3.
Figure 3. (a) East-west component �PGA=0.231 g�, and (b) North-south component �PGA=0.197 g�, and (b) Vertical component �PGA=0.085 g� of the accelerogram recorded at Abbotta-bad. (Courtesy of Pakistan Atomic Energy Commission 2005)
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 429
The 5% elastic response spectra for the east-west, north-south, and vertical compo-nents of the Abbottabad accelerogram are shown in Figure 4. The spectrum of the east-west component shows high amplification over a range from 0.5 to 1.5 sec with the high-est amplification of about 4 sec. This high amplification could put high demand on mediumto high rise buildings. If the design spectra of UBC 97, which is now part of the 2007 Build-ing Code of Pakistan, is plotted for Abbotabad, corresponding to zone 3 and soil profile D,the flat portion of the spectra renders spectral acceleration values of 0.9 g �2.5�0.36 g=0.9 g� which is very close to the value given by the computed response spectra.
As mentioned above, no strong motion data could be recorded near source, except atfew locations away from the epicenter. Peak ground acceleration (PGA) values could begenerated at different locations by using recorded data and attenuation relationships. Theattenuation relationship could be selected based on source mechanism, magnitude, ge-ology and local soil conditions. Keeping in view these criteria, Durrani et al. (2005) se-lected Ambraseys et al. (2005) attenuation relationship and utilized it to obtain estimatesof the PGA values (PGA=0.237 for soft soil and 0.194 for stiff soil) for Abbottabad.
BUILDING CODES IN PAKISTAN
Although frequent earthquakes of moderate magnitudes have occurred in Pakistan,but no serious efforts have been made regarding the assessment of seismic hazard andthe development and enforcement of a national seismic building code. Although city orregional bylaws are available for the regulation of architectural plans, they have no re-quirements regarding the structural analysis, design, and construction of buildings andother structures. In the absence of a national building code, foreign codes such as theAmerican Concrete Institute (ACI) Code and Uniform Building Code (UBC) have beenused.
Figure 4. Elastic response spectra (with 5% damping) for east-west, north-south and verticalcomponents of accelerogram recorded at Abbottabad.
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The Quetta earthquake of 30 May 1935 flattened the city of Quetta and resulted in60,000 casualties. The country’s first building code, known as Quetta Building Code(1937), was developed and enforced in 1937 by the British Government within the mu-nicipal limits of Quetta city. Unreinforced masonry buildings were forbidden. Eightmodular building designs were proposed for use in the different parts of Quetta. The firstmodular type, consisting of steel frame with reinforced concrete floor and reinforcedmasonry infill wall panels, was allowed to be used for buildings up to two stories highwith a maximum height of 8.2 m �27 ft�. Types 2 and 3 were reinforced brick masonrysingle-story buildings with reinforced concrete floors. Type 4 had a timber frame with infillpanels of brick or other materials. Types 5 and 6 were also of timber frame but differ in otheraspects from Type 4. Type 7 was of timber or steel frame with corrugated iron-sheet roofing,and Type 8 was rough ballie framework with Pise work. The first three types were required tobe designed to resist lateral forces equal to 12.5% of the weight of the structure above thesaid horizontal plane of the building. It was also made mandatory for the first time to providereinforced concrete bands 240 mm �9.5 in� in thickness with two 16 mm �5/8 in.� diam-eter steel bars at plinth, lintel, and roof levels (in case the roof is not reinforced concrete) inthe masonry buildings. The minimum thickness of the brick masonry wall was specified tobe 350 mm �13.5 in� and should be laid in 1:3 cement-sand mortar. Two 16 mm �5/8 in�diameter bars were required to be provided at all corners, at door and window openings andat horizontal intervals of 1.5 m �5 ft�. Guidelines were also provided for connecting trans-verse masonry walls. Limits on the dimensions of building, height of parapet walls, chim-neys and span of balconies were imposed. Specifications of building materials were also pro-vided in the code.
The Quetta building code was developed on the basis of observed behavior of build-ings and the engineering judgment of structural engineers. There are many similaritiesbetween the seismic and material provisions of this code and those of modern buildingcodes (e.g., Eurocodes 6 and 8). Buildings constructed in Quetta in compliance with thiscode were put to the test during an earthquake of magnitude 7.1 in September 1941, andthey performed extremely well (Jain and Nigan 2000). The Quetta building code wasenforced at a local level and not extended to other parts of the country.
In 1986, Pakistan Building Code (1986) was developed by the Federal Ministry ofHousing and Works. The seismic provisions of this code were based on the 1982 editionof the Uniform Building Code. The seismic zoning map of Pakistan of the 1986 Paki-stani Building Code is shown in Figure 5. The map was based on the Geophysical Centreof Quetta’s instrumental macro-earthquake data for the period of 1905 to 1979. The mapcould be applied for all structures except nuclear structures, large dams, and structurescontaining highly toxic chemicals. The area of Pakistan was divided into five seismiczones, i.e., Zone 0 through Zone 4. Zone 0 represents areas with negligible hazard (dam-age) while Zone 4 represents areas with significant seismic hazard (major damage cor-responding to intensity VII and higher on the 1931 MMI scale). Almost all the areasaffected by the Kashmir earthquake and Islamabad were placed in Zone 2 of the 1986Pakistan Building Code. However, the Kashmir earthquake produced earthquake inten-sities of VIII and higher in all major cities of the affected region.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 431
The code required all structures to be designed for the base shear, V, given by thefollowing equation:
V = ZIKCSW �1�
where Z is the seismic zone factor (Z=0.094 for Zone 0, Z=0.1875 for Zone 1, Z=0.375 for Zone 2 and Z=0.75 for Zone 3, Z=1 for a location very close to the activefault); I is the occupancy importance factor, K is a coefficient depending on the type of basicstructural system, C is a coefficient related with the fundamental elastic period of vibrationof the structure, S is a coefficient for site-structure resonance, and W is the weight of thestructure, including the partition loading and 25% of live load in case of storage and ware-house occupancy.
Figure 5. Seismic zoning map of Pakistan (PBC 1986).
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The 1986 Pakistani Building Code was an incomplete document as it lacked seismicprovisions for concrete, steel, and masonry buildings. The code was not officiallyadopted by the federal, provincial, or city governments. The absence of a seismic build-ing code resulted in substandard and deficient construction.
The Earthquake Rehabilitation and Reconstruction Authority (ERRA) was consti-tuted immediately after the Kashmir earthquake by the federal government, with a man-date to regularize the design and construction of government and public buildings in theearthquake affected areas. Buildings were required to be designed in accordance withthe provisions of UBC 97 until the development and implementation of a PakistanBuilding Code.
The 2007 edition of Pakistan Building Code (2007), containing detailed seismic de-sign parameters and criteria for seismic resistant design of buildings, was developed af-ter the 2005 Kashmir earthquake. The new code is mostly based on the 1997 edition ofthe Uniform Building Code (1997), American Concrete Institute Code (ACI 2005),ANSI/AISC 341-05, and ASCE (1993). The code has been adopted by Pakistan Engi-neering Council (PEC) and other relevant federal and provincial departments.
An updated seismic hazard map is included in this code (Figure 6). All the buildingsare required to be designed for a level of earthquake ground motion that has a 10% prob-
Figure 6. Seismic zoning map of Pakistan (PBC 2007).
ability of exceedance in 50 years. The area of Pakistan has been divided into five zones (1,
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 433
2A, 2B, 3, and 4) based on the peak ground acceleration. Balakot and Muzaffarabad areplaced in seismic Zone 4, while Abbottabad and Islamabad have been assigned to Zone 3 andZone 2B, respectively.
The design base shear, V, is given by the following formula:
V =Cv I
RTW �2�
where Cv is the seismic coefficient, I is the importance factor, T is the time period, W isthe total weight of the structure, and R is the response modification factor depending onthe horizontal load resisting system.
Upper and lower limits have been imposed on the design base shear. Near sourceeffects have been considered in the determination of design base shear. In the recent ver-sion of the code, modifications have been made in the provisions regarding masonrystructures involving requirements for minimum compressive strength of masonry units(8.25 MPa �1200 psi� for solid fired-clay bricks and 5.5 MPa �800 psi� for solid/hollowconcrete blocks), mix proportions and compressive strength of mortar (4.10 MPa�600 psi�), and compressive strength of masonry. Limitations on the number and height ofstories and minimum thickness of walls have also been specified. Because of the poor per-formance of stone masonry buildings in the Kashmir earthquake, use of rubble stone ma-sonry is prohibited. In order to increase the integrity and to ensure better performance of un-reinforced masonry buildings, use of reinforced concrete bond beams has been mademandatory at the plinth, door, and roof levels. Confined masonry has been introduced anddetailed provisions have been specified in the Code keeping in view its good performance inother parts of the world.
The chapter on masonry buildings lack explicit analysis and design procedures formasonry buildings. The response modification factors which represent the energy dissi-pation capacity of the different masonry building systems have not been provided. SincePakistan building code 2007 is a modified form of modern seismic building codes, ex-tensive indigenous research is required to calibrate the provisions of the Code. Researchis in progress to evaluate the performance of single- and double-story stone masonrybuildings with different levels of confinement (Ali 2009), and shake-table testing ofmodel unreinforced (Zakir 2009) and confined (Amjad 2009) brick masonry buildings isunderway to determine the seismic performance and response modification factors forthe respective class of buildings.
DESIGN AND CONSTRUCTION PRACTICES PREVALENT IN PAKISTAN
Stone, concrete block, and solid fired-clay masonry units have been traditionallyused as materials for the construction of single- and double-story buildings in Pakistan.Most masonry buildings were constructed with unreinforced masonry and were nonengi-neered, as explicit verifications of adequate resistance to seismic lateral forces were usu-ally not carried out.
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DESCRIPTION OF BUILDING TYPES
Adobe buildings have been the most common type of construction in the rural areas.In this type of construction, load-bearing walls, 400–450 mm �15.5–18.0 in� thick,were constructed from adobe brick or mud. The walls resisted high vertical loads of roof hav-ing 200–300 mm �8–12 in� of mud provided for insulation purposes. There was no properconnection between the orthogonal walls or between walls and roof. The heavy roof withweak walls made the building vulnerable to even low seismic excitations.
Single- and double-story unreinforced stone masonry buildings were the secondmost common form of building type adopted both in the urban and rural areas. Stonemasonry up to three stories high could be seen in the cities of Abbottabad and Muzaf-farabad. Building walls, usually 400–450 mm �15.5–18.0 in� thick, were constructedwith mud or weak cements-sand (1:8 or 1:10) mortar. Most of the buildings were constructedof rubble stone masonry. Orthogonal walls and walls and floor were not properly connected.These buildings usually have 150 mm �6 in.� thick reinforced concrete floor and roof and3.5–4.25 m �12–14 ft� story height. Wooden and steel truss with galvanized iron (GI)sheet were also used as the roofing system. Orthogonal walls and walls and floor were notproperly connected. The corners and junctions of walls were liable to failure because of thelack of proper connection. The buildings were vulnerable to out-of-plane failure due to in-clined roof and failure of external veneer because no band beams at roof level and throughstones were provided.
Another common type of building was single- or double-story unreinforced concreteblock masonry building. Single-leaf block masonry walls, usually 150–200 mm�6–8 in.� thick, were normally constructed with a weak cement-sand mortar (1:8). In thesebuildings, reinforced concrete slabs, usually 125–150 mm �5–6 in.� thick, were providedas floors and roofs. Typical story height was 3.0–3.5 m �10–11.5 ft�. Concrete blocks weremanufactured from cement, sand, and crushed stone in a semi-automatic machine. It was acommon practice to produce 80–100 blocks from one bag of cement with a mix proportionof 1:6:12 or 1:8:14. The average compressive strength of concrete blocks collected from theearthquake affected area, immediately after the earthquake, was found to be 0.75 MPa�110 psi�. Extremely low quality of materials (block and mortar) made the unreinforcedblock masonry more vulnerable to ground motion.
Unreinforced brick masonry system has been utilized for one- to three-story build-ings. Double-leaf load-bearing walls were usually 230 mm �9 in.� thick, and the storyheight was typically 3.0–3.5 m �10–11.5 ft�. However, no special arrangements weremade for connecting orthogonal walls. The walls laid in English bond gave good connectiv-ity. The workmanship in the brick masonry was comparatively better than the other types ofmasonry. Cement-sand mortar in the proportion of 1:6 or 1:8 was used. The floors and roofswere usually 125–150 mm �5–6 in.� thick reinforced concrete slab. The bricks were gen-erally of good quality having an average compressive strength of 14.5 MPa �2100 psi�.
Concrete-framed structures from two to five stories, on the other hand, were semi-engineered, in the sense that they were designed only for gravity loads. Structural de-signers used to model and design these buildings as skeletal structures ignoring the pres-
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 435
ence of masonry infill walls constructed from fired-clay bricks or concrete blocks. Noseparation or mechanical connection is provided at the interface of the unreinforced ma-sonry infill walls and the reinforced concrete columns or beams.
Ground floors of commercial buildings are mostly used as shops, with wide openingsin the front side and brick infill walls on the remaining three sides. Wide open spacesencompassing many bays are also common in these buildings. The upper floors of thesebuildings are used either as residential units or as stores for keeping goods for shopswith a load in excess of 4.8 kN/m2 �100 lbs/ ft2�. This type of multiple occupancy of asingle building, where ground floors have more open spaces compared to upper floors, andheavily loaded upper floors make the buildings more vulnerable to earthquake ground mo-tions. The vulnerability of the RC buildings was also increased with the use of poor qualityof concrete and poor detailing practice. Concrete mix was typically proportioned as 1:2:4(cement-sand-coarse aggregate) with no control on the water-to-cement ratio. Vibrator for thecompaction of structural concrete was seldom used.
The statistical overview of building stock in the earthquake-affected rural and urbanareas is given in Table 1. The overall percentage distribution of building stock is alsoprovided.
Figure 7 shows typical plans of brick and block masonry residential buildingsadopted in the areas affected by the Kashmir earthquake. The rooms are provided in asingle row or in L- or U-shaped arrangements. A veranda, supported by slender col-umns, is provided in front of the rooms (Figure 17). Building plans were being devel-oped with no adherence to the guidelines for ensuring reliable seismic behavior resultingin buildings with much smaller strength and stiffness in one direction than the other.Vertical and plan irregularities were common in the buildings. Walls are not symmetricin the orthogonal direction. Symmetry was also not followed in the vertical direction forthe walls and openings. Construction of unreinforced brick or block masonry on the ex-isting stone masonry walls was also observed in Muzaffarabad.
EFFECT OF EARTHQUAKES ON BUILT ENVIRONMENT
The buildings which were partially or fully damaged by this earthquake were esti-mated at about 450,000 (ADB-WB 2005) and includes buildings constructed with rein-
Table 1. Statistical overview of buildings in the affected area
forced concrete and unreinforced stone, concrete block, and brick masonry. Buildingsconstructed with rubble stone masonry suffered the heaviest damage followed by con-crete block masonry (Naseer et al. 2005). Almost 95% of the stone masonry buildings inthe earthquake-affected region were severely damaged. Damaged block masonry build-ings were estimated to be 60–65%. Brick masonry buildings performed comparativelybetter with only 5% buildings collapsed and 35% were severely damaged. In reinforcedconcrete buildings, 50–60% was partially or severely damaged.
In the following sections, damages to both reinforced and concrete buildings andtheir causes are discussed.
REINFORCED CONCRETE BUILDINGS
Reinforced concrete buildings (RC) could be categorized as semi-engineered be-cause they were usually designed for gravity loads only. These types of buildings alsosuffered heavy damages in the cities of Abbottabad, Manshera, Batagram, Balakot, andMuzaffarabad. The causes of failure could be attributed to a combination of the poordesign and construction practices. Lack of proper confinement in columns, insufficientlap length, strong beam-weak column, short column, and soft story were among the poordesign practices observed from the damaged buildings. Poor construction practices, in-cluding improper compaction of concrete, construction joint, and notching of concretecolumn for door and window lintel beam, were also observed to be responsible for dam-ages to concrete buildings.
Figure 7. Plans typically used for residential masonry buildings.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 437
POOR DETAILING PRACTICE
Because of the absence of a national seismic building code and its effective enforce-ment, buildings were poorly designed and detailed. This can be observed from the dam-aged buildings in Figures 8 and 9. This includes the lack of proper confinement in thecolumn, insufficient lap splice length and its location in the beam and column, use ofplain bars, and stirrups and ties with improper hooks. The ties in the column were uni-formly provided at a spacing of 300 mm �12 in.� or more, irrespective of the structuraldemand or code requirements; according to UBC 97 code, for moment resisting frames inseismic Zones 3 and 4, the maximum tie spacing should be the minimum of either one-quarter minimum member dimension or 100 mm �4 in�. The lap splice in the columns,240–720 mm �6–18 in.� in length, was normally provided at the base of the floor. How-
Figure 8. Failure due to insufficient confinement of concrete at beam-column joint. (Ties wereprovided at 12 in. spacing in 9 in. �18 in. concrete column of a commercial building inMuzaffarabad).
Figure 9. Failure of building columns in Abbottabad due to insufficient lap lengths.
438 NASEER ET AL.
ever, according to UBC 97, the lap splice for concrete frames located in seismic Zones 3 and4 should be provided within the center half of the column and should be proportioned astension splice. Because of the lack of confinement at the highly stressed zones (near beam-column joint) and insufficient lap length, stresses in the reinforcing bars could not be devel-oped which consequently resulted in the failure. These detailing deficiencies have been ob-served in almost 90–95% of reinforced concrete buildings in the cities of Abbottabad,Mansehra, Balakot, and Muzaffarabad.
STRONG BEAM-WEAK COLUMN
The least dimension of the column was commonly selected as equal to the dimensionof the infill masonry unit (230 mm �9 in.� with fired clay brick and 203 mm �8 in.� withconcrete block) so that the column would not be projected outward from the wall. The desireto have maximum space in the horizontal direction usually resulted in fewer columns withsmaller cross sections. Also, most of the concrete structures were designed for gravity loadsonly. Probably because of these reasons, buildings with strong beams and weak columnswere constructed. The weak nonductile columns suffered damage because of the lateral seis-mic demand, which could further be aggravated by axial forces from the elastic beams. Theexample of buildings damaged having strong beams and weak columns are illustrated inFigure 10.
SOFT-STORY EFFECT
The soft-story effect was more evident in commercial buildings than residential be-cause the ground floor is typically has more open spaces for shops and parking vehicles.This type of structural deficiency puts more deformation demand on the flexible lowerstory columns and because of the insufficient energy dissipation capacity of the col-umns, it resulted in the failure of lower stories. The buildings damaged by soft-storymechanism could be seen in the cities of Abbottabad, Manshera, Batagram, Balakot, andMuzaffarabad as shown in Figure 11.
Figure 10. Collapsed building due to strong beams and weak columns.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 439
CONSTRUCTION/WORKMANSHIP PROBLEM
The construction-related problems, including improper compaction of concrete andimproper treatment of construction joints, could not be ruled out as causes of failure inreinforced concrete buildings. Figure 12 shows poorly compacted concrete in columns.Vibrators are rarely used for the compaction of concrete in columns. The concretestrength estimated by Schmidt hammer test during the reconnaissance survey in bothprivate and public buildings rarely exceeded 13.75 MPa �2000 psi�.
Figure 11. Building failure due to soft story.
Figure 12. Poorly compacted column concrete.
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Notches were formed (Figure 13) in the concrete columns for accommodating lintelbeam over door and window opening, making the concrete section more vulnerable todamage. Improper treatment of construction joint resulting in sliding failure was alsoobserved in Muzaffarabad and shown in Figure 14.
Figure 13. Reduction in column cross section due to notch created to accommodate lintelbeam.
Figure 14. Damage at construction joint in Boys Hostel, Muzaffarabad.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 441
MASONRY BUILDINGS
IN-PLANE DAMAGES
Diagonal Shear Failure of Wall Piers
For heavily loaded masonry wall piers with low aspect ratios, in-plane shear forcesof the wall causes diagonal shear failure in the form of X-cracks. This type of failuredoes not endanger the gravity load-carrying capacity of a wall unless cracking becomessevere or out-of-plane movement takes place. The diagonal shear failure is also associ-ated with in-plane shear sliding of the masonry wall. Figure 15 shows building wallscracked in diagonal shear during the Kashmir earthquake. This type of failure could beseen throughout the affected area.
Flexure Failure of Pier
Piers with large aspect ratios fail in flexure under alternating bending momentscaused by the cyclic nature of the seismic forces. This type of failure manifests itself inthe form of horizontal cracks at the top and bottom ends of the pier. The cracked piermoves as a rigid body having no lateral-load resisting capacity (Bruneau 1994). Figure16 shows the flexure failures of wall piers in residential buildings.
Combined In-Plane and Out-of-Plane Effects
Masonry walls with openings are more susceptible to bidirectional (in-plane and out-of-plane) effects of ground shaking. In-plane shear cracks occur first which reduces thestrength of walls in the out-of-plane direction. This type of failure may be dangerous inthe case of out-of-plane sliding of the wall. Figure 17 shows combined in-plane and out-of-plane failure of the masonry walls.
Figure 15. Diagonal shear failures of masonry wall piers.
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OUT-OF-PLANE DAMAGES
Lateral Thrust from Inclined Roofs
Walls supporting an inclined roof experience lateral thrust in their out-of-plane di-rections. During strong ground shaking produced by an earthquake, this thrust may belarge enough to cause the walls to collapse in the out-of-plane direction or get seriouslydamaged. In the absence of reinforced concrete beams at the roof level, the building failsto produce a box-type behavior resulting in greater vulnerability of masonry walls in theout-of-plane direction. Figure 18 illustrate some failures of the buildings caused by thelateral thrust of the inclined roof. This type of failure is responsible for the collapse of alarge number of masonry buildings in Gari Habibullah, Balakot, and Kashmir.
Failure of Building Corners
The corners of walls supporting roofs inclined in both directions are damaged due tothe lateral thrust applied by the roof in addition to the inertial forces. The in-plane ro-
Figure 16. Flexural failures of masonry wall piers.
Figure 17. Combined in-plane and out-of-plane effects.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 443
tation of the rigid diaphragm also induces this type of failures at the corners. The lack ofproper connection between walls and between walls and floor make the corners morevulnerable to cracking. Figure 19 illustrate this type of failure.
Separation of Orthogonal Walls
Due to the lack of connection between orthogonal walls, separation of walls occursdue to out-of-plane vibration. The resistance offered by the in-plane walls to the bendingof out-of-plane walls depends on the tensile strength of masonry. Separation of orthogo-nal walls occurs whenever this tensile strength is exceeded. Shear stresses due to flange-action make the wall intersections more susceptible to cracking. Figure 20 shows sepa-ration of walls at intersection with other walls and floor.
Damages at Walls Adjacent to Roof
In many buildings, ventilators are constructed adjacent to floor slab with smalllength of wall in between them. Because of the out-of-plane vibration, these short piers
Figure 18. Collapse/damage of masonry walls due to lateral thrust from inclined roofs.
Figure 19. Damaged corners of buildings in Muzaffarabad.
444 NASEER ET AL.
get severely damaged. In some instances the piers get completely collapsed and the floorsettled down. Figure 21 shows damages to short piers adjacent to roofs in Muzaffarad,Gari Habibullah and Mansehra.
Collapse of External Veneer of Masonry Walls
The rubble stone masonry constructed in weak mortar and without providing throughstone are liable to fail at very low level of seismic excitation. The external veneer usuallyfails first in the out of plane direction. This type of failure (Figure 22) was more promi-nent in Gari Habibullah, the old city of Muzaffarabad, and the rural parts of the affectedarea.
Figure 20. Separation of walls due to lack of connection between orthogonal walls (left figureshows the damages due to main shock and was taken during building inventory survey inMuzaffarabad).
Figure 21. Damage at walls adjacent to roof (left figure shows the damages due to main shock
and was taken during building inventory survey in Muzaffarabad).
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 445
Out-of-Plane Failure of Gables
The collapse of gable walls was observed in many buildings of Muzaffarabad. Ab-sence of vertical loads and adequate connection between gable wall and roof, the gablewalls are more vulnerable to failure in the out-of-plane direction. Figure 23 shows col-lapsed gabled walls of two buildings in Muzaffarabad.
NONSTRUCTURAL MASONRY ELEMENTS
Out-of-Plane Failure of Infill Walls
Brick or block masonry have been commonly used in the construction of infill wallsin concrete framed buildings. After the construction of columns and beams, masonry in-fill panels are constructed with no separation between walls and columns while the gapbetween walls and beams are filled with mortar. Due to the lack of proper connection
Figure 22. Collapse of external veneer of stone masonry wall.
Figure 23. Out-of-plane failure of gables.
446 NASEER ET AL.
between walls and beams/columns, the infill walls are more susceptible to out of planefailure even for low level of ground shaking. Figure 24 shows out of plane failure ofinfill walls.
In-Plane Failure of Infill Walls
The concrete-framed buildings have typically been analyzed and designed as skeletalstructures without any masonry infill walls. On the other hand, buildings are constructedin such a manner that no separation is left between walls and beams/columns, resultingin a composite structure in which both concrete frame and infill masonry walls resisttogether the seismic demand of the earthquake ground motion. Consequently, the infillwalls fail in in-plane action and redistribution of loads occur, putting demand on thecolumn (Bruneau 2002). The infill walls of many concrete framed buildings were founddamaged in diagonal shear throughout the affected area. Crushing of masonry unit (con-crete blocks) was also observed.
FAILURES OF APPENDAGES SUPPORTED ON UNREINFORCED MASONRY
It has been a routine practice to build large water tanks at the top of the building, andthey are supported on vertical masonry elements. In concrete-framed structures, the wa-ter tanks are mostly simply supported on concrete columns. During ground shaking, sup-porting elements could not resist the increased structural demand resulting from inertialforces of the large mass of water. Consequently, dislocated water tanks severely dam-aged the buildings. Figure 25 illustrates the falling water tanks.
FAILURE OF BOUNDARY AND PARAPET WALLS
Normally, the boundary and parapet walls are constructed of single-leaf masonrywall. Boundary walls are 1.5 to 2.0 m �5 to 7 ft� in height, whereas parapet walls are 0.75to 1.5 �2.5 to 5 ft� high in the residential buildings of the affected area. The boundary andparapet walls throughout the affected area were either collapsed or severely damaged becauseof the strong ground motion. Figure 26 shows damaged boundary walls.
Figure 24. Out-of-plane failure of infill walls.
SEISMIC BEHAVIOR OF BUILDINGS IN PAKISTAN DURING THE 2005 KASHMIR EARTHQUAKE 447
No evidence of liquefaction or failure of buildings due to foundation failure wasfound. However, the details of slope failure could be found elsewhere.
CONCLUSIONS
Despite the fact that Pakistan is situated in a seismically active region, no seriousefforts had been undertaken for the assessment of seismic hazard and development of aseismic building code prior to the Kashmir earthquake. Buildings designed according to1937 Quetta building code performed well during the 1941 earthquake. The 1986 Paki-stan building code did not address the analysis and design of either concrete or masonrystructures for lateral loads. Seismic zoning maps given in the code underestimated theseismic hazard of the area affected by the Kashmir earthquake. The 2007 Pakistan Build-ing Code, developed after the Kashmir earthquake, is mostly based on the 1997 Uniform
Figure 25. Failure of appendages supported on unreinforced masonry elements (figures showthe damages due to main shock and were taken during building inventory survey inMuzaffarabad).
Figure 26. Failure of standing walls in Abbottabad.
448 NASEER ET AL.
Building Code. Indigenous research is required to evaluate analysis and design param-eters specific to materials and structural systems used in Pakistan.
It was observed during the reconnaissance surveys that most of the buildings werenonengineered or semi-engineered. The stone masonry buildings that comprised 30–35% of the building stock were severely damaged because the use of rubble stones, mudmortar, or weak cement-sand mortar (1:8 or 1:10) and lack of connection between wallsand walls and floor.
Concrete block masonry buildings were the second most damaged buildings. Thedamages could be attributed to use of very low strength blocks, lack of confinement ofunreinforced block masonry wall panels and poor workmanship. Brick masonry build-ings performed relatively well due to better workmanship and material properties. How-ever, the damage in brick masonry buildings could be attributed to the lack of confine-ment of wall panels and poor configuration.
Reinforced concrete buildings were mostly designed for gravity loads. However, itwas observed that reinforcement detailing did not even comply with code requirementsfor gravity load design. Improper confinement of the column joints, insufficient lapsplice length and lap location, soft story effect, and the use of extremely weak concretemay be attributed to the damages observed in the concrete buildings.
It is important to carry out risk and loss assessment of the major cities. Low-costretrofitting guidelines should be developed. Lastly, a strategy for the enforcement of aseismic code throughout Pakistan should be devised.
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(Received 13 November 2008; accepted 26 September 2009�
