A Note on The Strong Ground Motions and Behavior of ... · UET! A Note on The Strong Ground Motions...

!

!

!A Note on The Strong Ground Motions and Behavior of Buildings During 26th Oct. 2015 Afghanistan–Pakistan

Earthquake

!!!

December 2015

Presented to Earthquake Engineering Center, UET Peshawar

Peshawar, KP.

UET!

!

!

!

A Note on The Strong Ground Motions and Behavior of Buildings During 26th Oct. 2015 Afghanistan–Pakistan

Earthquake

Prepared by Dr. Naveed Ahmad, PhD, P.E. (Structures) Asst. Professor & Postgraduate Advisor – Earthquake Engineering Earthquake Engineering Center | Department of Civil Engineering UET Peshawar, KP. Signature:_____________________ Date: 13/12/2015 Prepared for

Director, Earthquake Engineering Center, UET Peshawar.

26th 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 !!!!!!!!!!!!!!!!!


Executive Summary This report presents a brief note on the 26th October 2015 Afghanistan-Pakistan Mw 7.5 earthquake, in reference to the ground motions observed in KP Pakistan and preliminary reconnaissance surveys conducted on the behavior assessment of structures in KP Pakistan subjected to the event. The ground motions acceleration is recorded in Peshawar and D.I. Khan by the National Center of Excellence in Geology, University of Peshawar, KP. The buildings damage assessment is carried out by the structural expert team of the Earthquake Engineering Center of UET Peshawar in the most affected regions in KP Pakistan (Abbottabad, Chitral, Dir, M0hmand Agency, Peshawar, Shangla, Swat), to understand the performance of structures against the earthquake induced ground motions and derive lessons learned from the earthquake event.


Background On Monday the 26th October 2015 at 02:09 PM (Pakistan Standard Time), an earthquake 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 followed by numerous aftershocks. The earthquake shaking has been felt significantly in Afghanistan, Pakistan and neighboring countries even at large distances (Figure 1) and observed to be one of the most damaging earthquakes in Pakistan. This earthquake has caused widespread destruction in Afghanistan and northern side of Pakistan. In Pakistan alone, the event resulted into the deaths of 232 people and injured other about 1500 people. The earthquake significantly affected structures and infrastructures: about 10 million building structures are damaged, which also included about 1400 school buildings (PDMA, 2015).

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


Observed Ground Motions The strong ground motions recorded in Peshawar and D.I. Khan districts of KP by the NCEG (NCEG 2015) are considered and analyzed for the engineering characterization and derivation of strong-motion parameters using signal processing and analysis software SeismoSignal (SeismoSignal 2015). Acceleration Time History Records Figure 2&3 shows the corrected acceleration time histories of ground motions recorded in Peshawar (280km source-to-site epicentral distance) and DI Khan (514km source-to-site epicentral distance). The time histories are processed applying 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 on the horizontal north component with bracketed time duration of 58.05sec and 0.038g is observed on the vertical component with bracketed time duration of 73.47sec. In DI Khan, peak ground acceleration of 0.026g is observed on the horizontal east component with bracketed time duration of 75.03sec, 0.036g is observed on the horizontal north component with bracketed time duration of 75.38sec and 0.015g is observed on the vertical component with bracketed time duration of 120.59sec. Acceleration Response Spectrum The acceleration time histories are used for the acceleration and displacement response analysis of elastic single degree of freedom oscillators (SDOF) with 5% damping to construct acceleration and displacement response spectrum for ground motions. The time period range 0 to 4.0 sec of SDOF systems is considered for the derivation of acceleration spectrum and time period range 0 to 10.0 sec of SDOF systems is considered for derivation of displacement response spectrum. 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 the predominant period of 0.38sec on the horizontal east component, 0.174g is observed at the predominant period of 0.28sec on the horizontal north component and 0.124g is observed at the predominant period of 0.18sec. Both the horizontal components acceleration spectrum shows peaks around 1.5sec and 2sec, which point to the presence of basin effects.


(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)

Acce

lerati

on (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)

Acce

lerati

on (g

)

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)

Acce

lerati

on (g

)

PGA = 0.038g


(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)

Acce

lerati

on (g

)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)

Acce

lerati

on (g

)

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)

Acce

lerati

on (g

)

PGA = 0.015g


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

Spec

tral A

ccele

ratio

n (g)

East ComponentNorth ComponentVertical 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)

Spec

tral A

ccele

ratio

n (g)

East ComponentNorth ComponentVertical Component

Tp = 0.64 Sec, SA = 0.144g

Tp = 0.14 Sec, SA = 0.052g

Tp = 0.40 Sec, SA = 0.092g


Displacement Response Spectrum In Peshawar, a maximum response displacement of 84.66mm is observed at the predominant period of 2.32sec on the horizontal east component, 110mm is observed 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 DI Khan, a maximum response displacement of 63.45mm is observed at the predominant period of 6.70sec on the horizontal east component, 57.42mm is observed at the predominant period of 5.36sec on the horizontal north component 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)

Spec

tral D

isplac

emen

t (mm)


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)

Spec

tral D

isplac

emen

t (mm

)


Tp = 6.70 Sec, SD = 63.45mm

Tp = 5.36 Sec, SD = 57.42mm

Tp = 6.16 Sec, SD = 65.68mm


Observed Behavior of Buildings In response to the damaging effects of earthquake event, the structural expert team visited various identified districts in Khyber Pakhtunkhwa (Abbottabad, Chitral, Dir, Mohmand Agency, Peshawar, Shangla, Swat) for preliminary damage assessment of buildings. The structural lessons learnt from the field observations in KP, on the seismic behavior and performance of buildings, are briefly described. Adobe & Stone Masonry Structures Rubble stone masonry structures in dry condition or mud mortar and adobe/mud structures performed very poorly in this earthquake and have shown severe damages, partial and total collapses. It is due to the low strength of materials and poor construction practice (not using any confining beam and column elements). Furthermore, due to raining few days before the earthquake event, these structures were in wet condition when subjected to ground motion shaking, thus possesses less strength. Topographic effects at ridges have also played role in amplifying ground motions and increasing time duration of shaking, because of focusing of seismic waves. These observations are primarily made in the mountainous region of Dir, Mohmand Agency, Chitral and Swat. During the field survey, it was observed that the building owners have re-constructed their damaged and collapsed building using the same building materials (stone and mud) and construction practice, thus, retaining the risk for future events. Brick Masonry Structures Brick masonry structures of very old construction, 70-80 years older, also performed very poorly in Peshawar, due to building materials deterioration because of aging. These buildings have shown severe damages and roof collapses. However, the same structures where timber-framing laces were used, performed well and the structures remain intact. These observations were made in Peshawar, particularly in Awqaf buildings. Brick masonry and brick masonry confined structures have performed poorly and have shown severe damages in case of ground motion amplification on alluvium soil due to local site effects or due to localized foundation settlement. Poor performance of confined masonry structures was also observed due to improper construction of these structures, particularly confining elements were built before


the masonry walls and no toothing of RC elements to masonry walls has been carried out. These observations have been made in Upper Dir and Malakand. Reinforced Concrete Structures The recently constructed reinforced concrete structures in KP are those primarily designed to the building code of Pakistan (BCP 2007, UBC 97), which are detailed as per the ACI-318 recommendations (ACI 318-05/08). These structures have performed very well, as per the expectation, during the earthquake. In few cases, damages like horizontal and vertical cracks have been observed in these structures at the infill-frame interfaces and minor diagonal cracks have been observed in masonry infill, primarily in regions where ground motions were amplified due to local site conditions. Similar observations have been made in the valley of Abbottabad. In case of reinforced concrete structures deigned to gravity or undersigned, damages have been observed also in the structural members, particularly in the columns. The damages in these structure types are aggravated due to local site effects. These observations have been made in Peshawar. Conclusions: Lessons Learnt The following conclusions are drawn from the earthquake ground motions and observed building performance during the earthquake event. Ground Motions

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

• Due to the large frequency contents of seismic waves, the ground shaking observed 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 the presence of basin effects in Peshawar, which are an important observation particularly for the design of long period structures like bridges and tall buildings. The basin effects at Peshawar may be more pronounced in case of large and deep earthquakes in the near vicinity, which can pose more risk on long period structures.


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

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

• Many buildings of non-engineered (adobe & rubble masonry) and semi-engineered (brick masonry & confined masonry) constructions have incurred severe damages and experienced partial and total collapses and performed poorly in case of ground motion amplification due to soft-soil conditions and topographic effects (ridges effects). This point to the importance of site-soil & site-topography consideration in the design and construction of structures. The poor performance of confined masonry buildings also attributed to the improper construction practice – no toothing was observed between column and masonry i.e. confining columns were built first and masonry after. However proper confined masonry construction requires building the masonry wall first, after placing reinforcement skeleton for confining columns, and then poor concrete for columns later.

• Significant amount of medium to good quality constructions (brick masonry buildings) have performed very poorly in case of local differential settlement due to local soil failure, which was primarily due to improper drainage and blockage, causing water ponding, that kept the foundation soil wet for years and resulted in the foundation soil to loose its shear strength capacity for carrying vertical and lateral loads. This calls for attention 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 to the 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 these structures have been observed which calls for attention in future designs to use soft joint filler in expansion joints to minimize hammering effects during earthquake.

• Structures with timber laces and timber framing have performed better, even in case of using low strength infill materials. However, in case of large panels, masonry materials detachment and panel out-of-plane failure have been observed.

Acknowledgement: The author is thankful to Prof. Dr. Tahir, Director of the National Center 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 of postgraduate students of the Department of Civil Engineering of UET Peshawar, who conducted survey for building damage assessment and reported their findings in terms of photos and field observations. The author would like to thank the following in particular, 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,” Technical Report, 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 of Peshawar, Peshawar, KP.

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

SeismoSignal (2015) “SeismoSignal: A software for processing and analyzing earthquake strong-motion data”, Earthquake Engineering Software Solutions, Pavia, ITALY.

USGS (2015) “M7.5 – 45 km E of Farkhar, Afghanistan”, United States Geological Survey (USGS), USA.

(URL: http://earthquake.usgs.gov/earthquakes/eventpage/us10003re5#) UBC (1997) “Uniform building code”, International Council of Building Official,

Whittier, CA, USA.


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


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 continuous wall at expansion joints in the slab, in-plane shear damages in loadbearing walls and damages observed in confined brick masonry building due local site effects.


Figure 10 Damages observed in reinforced concrete buildings – most likely damage mechanisms. 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 horizontal cracking at roof diaphragm movement.

A Note on The Strong Ground Motions and Behavior of ... · UET! A Note on The Strong Ground Motions...

Documents

Transcript of A Note on The Strong Ground Motions and Behavior of ... · UET! A Note on The Strong Ground Motions...