26th October 2015 Earthquake

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A Note on The Strong Ground Motions and Behavior ofBuildings During 26th Oct. 2015 Afghanistan–PakistanEarthquake

December 2015

Presented to Earthquake Engineering Center, UET PeshawarPeshawar, KP.


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26 th October 2015 Afghanistan-Pakistan Earthquake | © Dr. Naveed Ahmad 1/15

Contents of Report

Executive Summary ............................................................................................ 2

Background ......................................................................................................... 3 Observed Ground Motions ................................................................................. 4 Acceleration Time History Records ................................................................................... 4 Acceleration Response Spectrum ..................................................................................... 4 Displacement Response Spectrum ................................................................................... 8

Observed Behavior of Buildings ....................................................................... 9 Adobe & Stone Masonry Structures .................................................................................. 9 Brick Masonry Structures .................................................................................................. 9 Reinforced Concrete Structures ...................................................................................... 10

Conclusions: Lessons Learnt .......................................................................... 10

Ground Motions .............................................................................................................. 10 Buildings Performance .................................................................................................... 11

References ........................................................................................................ 12


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Executive Summary

This report presents a brief note on the 26 th October 2015 Afghanistan-PakistanMw 7.5 earthquake, in reference to the ground motions observed in KP Pakistanand preliminary reconnaissance surveys conducted on the behavior assessmentof structures in KP Pakistan subjected to the event. The ground motionsacceleration is recorded in Peshawar and D.I. Khan by the National Center ofExcellence in Geology, University of Peshawar, KP. The buildings damageassessment is carried out by the structural expert team of the EarthquakeEngineering Center of UET Peshawar in the most affected regions in KPPakistan (Abbottabad, Chitral, Dir, M0hmand Agency, Peshawar, Shangla,Swat), to understand the performance of structures against the earthquakeinduced ground motions and derive lessons learned from the earthquake event.


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Background

On Monday the 26 th October 2015 at 02:09 PM (Pakistan Standard Time), anearthquake of Mw 7.5 occurred in the Hindu Kush Mountains, at an intermediate

depth of about 210 km, within 48 km SSW of Jarm Afghanistan that was followedby numerous aftershocks. The earthquake shaking has been felt significantly inAfghanistan, Pakistan and neighboring countries even at large distances (Figure1) and observed to be one of the most damaging earthquakes in Pakistan.

This earthquake has caused widespread destruction in Afghanistan and northernside of Pakistan. In Pakistan alone, the event resulted into the deaths of 232people and injured other about 1500 people. The earthquake significantlyaffected structures and infrastructures: about 10 million building structures aredamaged, which also included about 1400 school buildings (PDMA, 2015) .

Figure 1 Ground shaking severity, in terms of PGA, calculated and observed (in terms ofintensity) for the 26 th October 2015 Afghanistan-Pakistan earthquake (USGS 2015).


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Observed Ground Motions

The strong ground motions recorded in Peshawar and D.I. Khan districts of KPby the NCEG ( NCEG 2015 ) are considered and analyzed for the engineering

characterization and derivation of strong-motion parameters using signalprocessing and analysis software SeismoSignal ( SeismoSignal 2015 ).

Acceleration Time History Records

Figure 2&3 shows the corrected acceleration time histories of ground motionsrecorded in Peshawar (280km source-to-site epicentral distance) and DI Khan(514km source-to-site epicentral distance). The time histories are processedapplying the baseline correction and Butterworth Bandpass filtering (0.01-50 Hz).In Peshawar, peak ground acceleration of 0.05g is observed on the horizontal

east component with bracketed time duration of 61.12sec, 0.053g is observed onthe horizontal north component with bracketed time duration of 58.05sec and0.038g is observed on the vertical component with bracketed time duration of73.47sec. In DI Khan, peak ground acceleration of 0.026g is observed on thehorizontal east component with bracketed time duration of 75.03sec, 0.036g isobserved on the horizontal north component with bracketed time duration of75.38sec and 0.015g is observed on the vertical component with bracketed timeduration of 120.59sec.

Acceleration Response Spectrum

The acceleration time histories are used for the acceleration and displacementresponse analysis of elastic single degree of freedom oscillators (SDOF) with 5%damping to construct acceleration and displacement response spectrum forground motions. The time period range 0 to 4.0 sec of SDOF systems isconsidered for the derivation of acceleration spectrum and time period range 0 to10.0 sec of SDOF systems is considered for derivation of displacement responsespectrum. Figure 4&5 shows the calculated acceleration response spectrum,Figure 6&7 shows the calculated displacement response spectrum.

In Peshawar, a maximum response acceleration of 0.215g is observed at thepredominant period of 0.38sec on the horizontal east component, 0.174g isobserved at the predominant period of 0.28sec on the horizontal northcomponent and 0.124g is observed at the predominant period of 0.18sec. Boththe horizontal components acceleration spectrum shows peaks around 1.5secand 2sec, which point to the presence of basin effects.


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(Horizontal East Component)

PGA = 0.05g, Bracketed Duration = 61.12sec

(Horizontal North Component)


(Vertical Component)

PGA = 0.038, Bracketed Duration = 73.47sec

Figure 2 Acceleration time histories of ground motions recorded in Peshawar.

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)

A c c e l e r a t i o n ( g )

PGA = 0.05g

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)


PGA = 0.053g

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)


PGA = 0.038g


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(Horizontal East Component)


(Horizontal North Component)


(Vertical Component)

PGA = 0.015, Bracketed Duration = 120.59sec

Figure 3 Acceleration time histories of ground motions recorded in DI Khan.

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)


PGA = 0.026g

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)


PGA = 0.036g

0 20 40 60 80 100 120 140 160

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time (sec)


PGA = 0.015g


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In DI Khan, a maximum response acceleration of 0.144g is observed at thepredominant period of 0.64sec on the horizontal east component, 0.092g isobserved at the predominant period of 0.40sec on the horizontal northcomponent and 0.052g is observed at the predominant period of 0.14sec. Thepeaks observed in acceleration response spectrum of Peshawar at longer period,which is due to basin effects, are not clearly observed for ground motionsobserved in DI Khan.

Figure 4 Acceleration response spectrum of ground motions recorded in Peshawar.

Figure 5 Acceleration response spectrum of ground motions recorded in DI Khan.

0 0.5 1 1.5 2 2.5 3 3.5 40

0.05

0.1

0.15

0.2

0.25

Time Period (sec)

S p e c t r a l A c c e l e r a t i o n ( g )

East ComponentNorth Component

Vertical ComponentTp = 0.28 Sec, SA = 0.174g

Tp = 0.18 Sec, SA = 0.124g

Tp = 0.38 Sec, SA = 0.215g

0 0.5 1 1.5 2 2.5 3 3.5 40

0.05

0.1

0.15

0.2

0.25

Time Period (sec)

S p e c t r a l A c c e l e r a t i o n ( g )

East ComponentNorth Component

Vertical Component

Tp = 0.64 Sec, SA = 0.144g

Tp = 0.14 Sec, SA = 0.052g

Tp = 0.40 Sec, SA = 0.092g


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Displacement Response Spectrum

In Peshawar, a maximum response displacement of 84.66mm is observed atthe predominant period of 2.32sec on the horizontal east component, 110mm isobserved at the predominant period of 3.48sec on the horizontal north

component and 38.32 is observed at the predominant period of 5.88sec. In DIKhan, a maximum response displacement of 63.45mm is observed at thepredominant period of 6.70sec on the horizontal east component, 57.42mm isobserved at the predominant period of 5.36sec on the horizontal northcomponent and 65.68mm is observed at the predominant period of 6.16sec.

Figure 6 Displacement response spectrum of ground motions recorded in DI Khan.

Figure 7 Displacement response spectrum of ground motions recorded in DI Khan.

0 1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

120

Time Period (sec)

S p e c t r a l D i s p l a c e m e n t ( m

m )

East Component

North ComponentVertical Component

Tp = 3.48 Sec, SD = 110mm

Tp = 5.88 Sec, SD = 38.32mm

Tp = 2.32 Sec, SD = 84.66mm

0 1 2 3 4 5 6 7 8 9 100

20

40

60

80

100

120

Time Period (sec)

S p e c t r a l D i s p l a c e m e n t ( m m )

East Component

North ComponentVertical Component

Tp = 6.70 Sec, SD = 63.45mm

Tp = 5.36 Sec, SD = 57.42mm

Tp = 6.16 Sec, SD = 65.68mm


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Observed Behavior of Buildings

In response to the damaging effects of earthquake event, the structural expertteam visited various identified districts in Khyber Pakhtunkhwa (Abbottabad,Chitral, Dir, Mohmand Agency, Peshawar, Shangla, Swat) for preliminarydamage assessment of buildings. The structural lessons learnt from the fieldobservations in KP, on the seismic behavior and performance of buildings, arebriefly described.

Adobe & Stone Masonry Structures

Rubble stone masonry structures in dry condition or mud mortar and adobe/mudstructures performed very poorly in this earthquake and have shown severedamages, partial and total collapses. It is due to the low strength of materials andpoor construction practice (not using any confining beam and column elements).Furthermore, due to raining few days before the earthquake event, thesestructures were in wet condition when subjected to ground motion shaking, thuspossesses less strength. Topographic effects at ridges have also played role inamplifying ground motions and increasing time duration of shaking, because offocusing of seismic waves. These observations are primarily made in themountainous region of Dir, Mohmand Agency, Chitral and Swat. During the fieldsurvey, it was observed that the building owners have re-constructed theirdamaged and collapsed building using the same building materials (stone andmud) and construction practice, thus, retaining the risk for future events.

Brick Masonry Structures

Brick masonry structures of very old construction, 70-80 years older, alsoperformed very poorly in Peshawar, due to building materials deteriorationbecause of aging. These buildings have shown severe damages and roofcollapses. However, the same structures where timber-framing laces were used,performed well and the structures remain intact. These observations were madein Peshawar, particularly in Awqaf buildings.

Brick masonry and brick masonry confined structures have performed poorly andhave shown severe damages in case of ground motion amplification on alluviumsoil due to local site effects or due to localized foundation settlement. Poorperformance of confined masonry structures was also observed due to improperconstruction of these structures, particularly confining elements were built before


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the masonry walls and no toothing of RC elements to masonry walls has beencarried out. These observations have been made in Upper Dir and Malakand.

Reinforced Concrete Structures

The recently constructed reinforced concrete structures in KP are those primarilydesigned to the building code of Pakistan (BCP 2007, UBC 97) , which aredetailed as per the ACI-318 recommendations ( ACI 318-05/08 ). These structureshave performed very well, as per the expectation, during the earthquake. In fewcases, damages like horizontal and vertical cracks have been observed in thesestructures at the infill-frame interfaces and minor diagonal cracks have beenobserved in masonry infill, primarily in regions where ground motions wereamplified due to local site conditions. Similar observations have been made in thevalley of Abbottabad.

In case of reinforced concrete structures deigned to gravity or undersigned,damages have been observed also in the structural members, particularly in thecolumns. The damages in these structure types are aggravated due to local siteeffects. These observations have been made in Peshawar.

Conclusions: Lessons Learnt

The following conclusions are drawn from the earthquake ground motions andobserved building performance during the earthquake event.

Ground Motions

• Despite the large source-to-site distance and deep nature of theearthquake source (hypocenter), significant ground motions have beenobserved in KP Pakistan in this earthquake, which is due to the large sizeof the earthquake releasing high seismic energy.

• Due to the large frequency contents of seismic waves, the ground shakingobserved in Peshawar has been amplified at various fundamental

frequencies of the site.• Amplification at longer periods (around 1.5sec and 2.2/2.3sec) point to thepresence of basin effects in Peshawar, which are an importantobservation particularly for the design of long period structures like bridgesand tall buildings. The basin effects at Peshawar may be morepronounced in case of large and deep earthquakes in the near vicinity,which can pose more risk on long period structures.


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Buildings Performance• The high amount of building collapses observed in this earthquake event,

despite the moderate shaking severity, point to the very high vulnerabilityof building stock in the KP Province of Pakistan.

•

Many buildings of non-engineered (adobe & rubble masonry) and semi-engineered (brick masonry & confined masonry) constructions haveincurred severe damages and experienced partial and total collapses andperformed poorly in case of ground motion amplification due to soft-soilconditions and topographic effects (ridges effects). This point to theimportance of site-soil & site-topography consideration in the design andconstruction of structures. The poor performance of confined masonrybuildings also attributed to the improper construction practice – no toothingwas observed between column and masonry i.e. confining columns were

built first and masonry after. However proper confined masonryconstruction requires building the masonry wall first, after placingreinforcement skeleton for confining columns, and then poor concrete forcolumns later.

• Significant amount of medium to good quality constructions (brick masonrybuildings) have performed very poorly in case of local differentialsettlement due to local soil failure, which was primarily due to improperdrainage and blockage, causing water ponding, that kept the foundationsoil wet for years and resulted in the foundation soil to loose its shearstrength capacity for carrying vertical and lateral loads. This calls forattention to improve building drainage systems.

• Buildings designed to the recent seismic building code of Pakistan & UBC-97 and detailed as per the ACI recommendations have performed up tothe expectations, even in case of ground motions amplification. However,damage to infill walls have been observed, which calls for using soft(flexible) infill in these structures. Furthermore, pounding effects in thesestructures have been observed which calls for attention in future designsto use soft joint filler in expansion joints to minimize hammering effectsduring earthquake.

Acknowledgement: The author is thankful to Prof. Dr. Tahir, Director of the NationalCenter of Excellence in Geology, University of Peshawar for kindly providing the strong-motion data recorded in Peshawar and DI Khan. The author thank the contributions ofpostgraduate students of the Department of Civil Engineering of UET Peshawar, whoconducted survey for building damage assessment and reported their findings in terms


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of photos and field observations. The author would like to thank the following inparticular, for their valuable contributions:Engr. Nouman Khan, United Arab Emirates University (UAEU), Al Ain Dubai, UAE.Engr. Noor Ullah, MSc Scholar, Structural Engineering, UET Peshawar.Engr. Irshad Khan, MSc Student, Structural Engineering, UET Peshawar.

References

ACI-318-05/08 (2005/2008) “Building code requirements for structural concrete(ACI 318-05) and commentary (ACI318R-05/08),” Technical Report,American Concrete Institute (ACI), P.O.Box. 9094, Farmington Hills,Michigan, USA.

BCP (2007) “Building code of Pakistan: Seismic Provisions-2007,” TechnicalReport, Ministry of Housing and Works, Islamabad, Pakistan.

NCEG (2015) “Acceleration time history records for D.I. Khan and Peshawar”,National Center of Excellence in Geology (NCEG), University ofPeshawar, Peshawar, KP.

PDMA (2015) “Damages and Relief Report – Report on damages andcompensation due to 26 th October 2015 earthquake”, Provincial DisasterManagement Authority (PDMA), Government of Khyber Pakhtunkhwa,Peshawar, KP.

SeismoSignal (2015) “SeismoSignal: A software for processing and analyzingearthquake strong-motion data”, Earthquake Engineering SoftwareSolutions, Pavia, ITALY.

USGS (2015) “M7.5 – 45 km E of Farkhar, Afghanistan”, United StatesGeological Survey (USGS), USA.(URL: http://earthquake.usgs.gov/earthquakes/eventpage/us10003re5# )

UBC (1997) “Uniform building code”, International Council of Building Official,Whittier, CA, USA.


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Figure 8 Damages observed in adobe and rubble stone masonry structures – most likely damagemechanisms. Form top to bottom: corner damages, delamination, partial wall collapse and totalstructural collapse.


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Figure 9 Damages observed in brick masonry buildings – most likely damage mechanisms. Form

top to bottom: in-plane wall damages due to local settlement, damage to slab and continuouswall at expansion joints in the slab, in-plane shear damages in loadbearing walls and damagesobserved in confined brick masonry building due local site effects.


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26 th October 2015 Afghanistan-Pakistan Earthquake | © Dr Naveed Ahmad 15/15

Figure 10 Damages observed in reinforced concrete buildings – most likely damagemechanisms. Form top to bottom: flexure cracking in gravity/under-designed RC structures,pounding at the expansion joints, in-plane shear damages in masonry infill and horizontalcracking at roof diaphragm movement.

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26th October 2015 Earthquake