dynamic response of uae buildings earthquakes

Dynamic Response of UAE Buildings Earthquakes

Dr. Jamal A. Abdalla, M. ASCE, M. EERI

Associate Professor and Chair of Civil Engineering Department

American University of Sharjah

Gulf Seismic Forum 2005February 20-23, 2005, Al-Ain, UAE

Outline• Geology, tectonics and seismicity of UAE

• Seismic hazard assessment of UAE

• Types of Buildings in UAE

• Earthquake Resistant Design Provisions • Dynamic response of Villas to

earthquakes

• Results and discussions• Conclusion and Future Work


Geology of UAE

• Geologically, the features of UAE follow that of the Arabian Platform

• The rocks in the Arabian Platform accumulated on stable marine shelf

• sandstones, siltstones, carbonates and salt basin characterize the region


Tectonics of UAE• Tectonically, UAE is situated in the South-Eastern part of the

Arabian plate that is composed of sedimentary rocks that range in thickness from zero to 10 km, in addition to basalt and oceanic basin

• There are several major fault systems that surround the Arabian Plate.

• The northwest boundary of the Arabian Plate is the left-lateral Dead Sea Fault Zone.

• The southeast boundary of the Arabian Plate is the Owen Fracture Zone (OFZ) in the northwestern Indian Ocean.

• The western boundary of the Arabian Plate is the Red Sea Rift and Sheba Ridge systems.

• The seismicity of few of these directly affects the seismicity of UAE. • The eastern boundry of the Arabian Plate is the Zagros Fold &

Thrust Belt and Makran Subduction Zone which are the only two fault systems that have direct effect on UAE seismicity.


Tectonics of UAE

TurkishPlate

African Plate

Arabian Plate

Indian Plate

EurasianPlate

Owen Fracture Zone

Zagros Fold Belt

Dead SeaFault

Red SeaFault

Makran Subduction


Seismicity of UAE

Bahrain

Qatar

United Arab Emirates

Iran

Sultanate of OmanKingdom of Saudi Arabia

Gulf of Oman

Arabian/Persian Gulf

5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00

Nor

th L

atitu

de


Siesmic Hazard Assessment

• The eastern portion of the Arabian Peninsula (UAE, Qatar, Bahrain, Kuwait, Northern Oman) were excluded from previous SHA studies

• A seismic hazard assessment was conducted for UAE and its vicinity

• The probabilistic approach, that takes into account the uncertainties in the level of earthquake magnitude, its hypocentral location, its recurrence relation and its attenuation relation is used


Seismic zoning map of UAE and its vicinity for 50 years period with 10% probability of being

exceeded

Zone 3

Bahrain

Qatar


Iran


Gulf of Oman


5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00N

orth

Lat

itude

Zone 0

Zone 1

Zone 2A

Zone 2B


Seismic Zone Factor (Z)

• Large parts of UAE, specifically Southern UAE, lies within Zone 0 Greater Abu Dhabi area lies within Zone 1.

• Fujaira, greater Dubai, Sharjah and Ajman area lies within Zone 2A.

• No part of UAE lies within Zone 2B or Zone 3.


Factors affecting Dynamic Response of buildings

• To design buildings to resist earthquake forces, several factors must be considered. Such factors can be divided into the following five categories:

• seismological factors such as seismic zone on which the structure is to be constructed

• geotechnical factors such as soil type, soil profile, soil dynamic properties and its liquefaction potential

• structural factors such as lateral force resisting systems and dynamic properties of the buildings

• architectural factors such as building shape and form • social factors such as building occupancy importance.


Analysis Methods• To include the earthquake ground motion effect,

buildings can be analyzed using different static and dynamic methods. Such methods include:

• Equivalent static method• Response spectrum method• Time history method• Push-over method. • For low and medium rise regular buildings in low

and moderate seismic activity zones, the equivalent static method has been adopted predominately by almost all building codes. The equivalent static method formula is very much a function of similar factors.


Equivalent Static Method• The most widely used equivalent static method formula is that of

the Uniform Building Code (UBC-94) adopted from SEAOC. This formula is the basis of most formulas found in other codes and it will be adopted here.

• The equivalent static method calculates the lateral seismic base shear which is a function of many factors.

• The base shear in a buildings can be calculated using the following formula (UBC-94):

WR

ZICV

w

where:Z = Seismic zone factor; I = Importance factor; W = Weight of the building, total

dead load and a percentage of live load; Rw = Numerical seismic coefficient (Response Modification Factor); C = Numerical coefficient.


Gulf Seismic Forum 2005

February 20-23, 2005, Al-Ain, UAE

Seismic Zone Factor (Z)• The Z-value represents the maximum effective

peak acceleration (EPA) and is expressed as a fraction of the gravitational acceleration, g. The peak ground acceleration (PGA) are adjusted to give the effective peak acceleration EPA. The results are listed below

Zone Number PGA ( g) Z

0 Less than 0.05 0.05

1 0.05 - 0.1 0.08

2A 0.1 - 0.20 0.16

Spectral Acceleration Coefficient (C)

• This coefficient is to account for the spectral amplification of ground motion based on structure fundamental period (T) and site response factor (S).

3

2

25.1

T

SC

The empirical formula for calculating fundamental period of vibration of buildings (in seconds) according to (UBC-94) is given by:

4

3

)( nt hCT


Other Factors I and Rw

• The importance factor, I, is determined based on the building importance and is used to provide for more conservative design for important facilities. The importance factor ranges from 1.0 for single family dwellings to 1.5 for building needed immediately after earthquake such hospitals, power stations and the like.

• The response modification factor, Rw, is introduced to account for the reduction in structural response caused by damping of the structure and its inelastic response. The response modification factor ranges from 5 for masonry bearing wall system to 12 for dual systems with special-moment-resisting frame.


Types of Building in UAE• Concrete buildings are the dominant types of

structural systems in UAE. • Modern single family residential buildings are

predominately two story reinforced concrete buildings with a substantial set back in their third story.

• Old houses are one story reinforced concrete or masonry structures.

• Industrial and commercial buildings range from three stories to 30 stories with the majority in the range of five to ten stories.

• There are few steel structures which are mainly industrial hangers and warehouses.


Types of Building in UAE• Floor systems used on constructing buildings in

UAE include slabs with beams, flat plate, hollow block slabs and occasionally waffle slabs and they can be modeled as rigid diaphragms.

• Residential buildings are characterized by vertical geometric irregularities, mass irregularities and plan structural irregularities.

• Most modern reinforced concrete buildings can be classified as ordinary moment resisting frames (OMRF) with fixed bases.

• The commercial buildings usually have mezzanine wooden floors that can be modeled as flexible diaphragms and shear walls that classify them as dual systems.


Types of Building in UAE

Single Family villa Apartment Building Commercial Building


Gulf Seismic Forum 2005


Near-Field vs Far-Field Earthquakes

• Near-Field Earthquake– Characterized by:

• Large amplitudes• Large frequency• High velocity pulses

• Far-Field Earthquakes– Characterized by:

• Small amplitudes • Small frequency• More consistent movements

Acceleration Time History for Dibba Earthquake, October 21, 2004

0 1 2 3 4 5 6 7 8 9 10-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

time

disp

lace

men

t

East-West DirectionGulf Seismic Forum 2005



North-South DirectionGulf Seismic Forum 2005


0 1 2 3 4 5 6 7 8 9 10-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

time

disp

lace

men

t


Vertical DirectionGulf Seismic Forum 2005


0 1 2 3 4 5 6 7 8 9 10-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

time

disp

lace

men

t

Acceleration Time History Recorded at

AUS Station in Masafi, December 2002

0 1 2 3 4 5 6 7-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Time (s)

Accele

ration (

g)


Acceleration Response Spectra (AUS

Station in Masafi, December 2002)


Conclusions and Future Work• Three major elements of an earthquake design code, mainly seismic zoning,

dynamic characteristics of common types of buildings and design response spectra were addressed in details and some recommendations were made. However, there are several factors that need to be specialized for UAE. In order to do so the following miles stones need to be achieved

• Evaluation of relationship between buildings types, their width, their height and their fundamental period of vibration (T).

• Determination of local site effect (S) and soil parameters for the common types of soils in UAE for amplification or attenuation of ground motion.

• Development of design response spectra for areas of critical structures.• Evaluation of response modification factor (Rw) for buildings.• Evaluation of importance factors for buildings (I), elements, components and

equipments.• Development of attenuation relationships for UAE to fine tune the seismic

hazard map developed based on Zagros attenuation relation.• Study of the liquefaction potential of the different types of soils of UAE.• Installation of strong motion recorders (Seismometers) to record strong

ground motion in different parts of the country and in major installations.• Instrumentation of critical and historical buildings and monitoring of their

response.• Study earthquake codes of surrounding countries.


Acknowledgment The support for the research presented inthis paper had been provided by the American University of Sharjah, Faculty Research Grant. Strong motion records are

recorded by AUS Earthquake Observatory. This support is gratefully acknowledged. The views and conclusions

are those of the author and should not be taken as those of the sponsor.


Thank You

EARTHQUAKE RESISTANT DESIGN CODES: BACKGROUND

• The objectives of an earthquake resistant design code in general is to promote and protect the health, life and the economic well-being of the society in the event of severe and moderate earthquakes

• Codes usually specify minimum standards for construction material, minimum strength for structural elements to prevent failure and maximum deformations or displacements (serviceability) to prevent excessive deflection, vibration and cracking.

• Specification of structural detailing is usually given to ensure the desired ductile behavior of structural elements.

• The code intention is to provide minimum probability of failure and largest probability of serviceability.

• It is observed that engineered buildings are unlikely to experience structural damage or complete failure or collapse as the result of the effects of dead, live, or wind loads. However, in the event of severe earthquakes buildings are likely to behave in-elastically and the ultimate objective of the earthquake resistant design code is to prevent collapse of buildings while tolerating reasonable amount of structural damage.


EARTHQUAKE RESISTANT DESIGN CODES: BACKGROUND

• Almost all developed codes follow one the following pioneering code which are based on similar concept.

• The pioneering code is the Uniform Building Code that is greatly influenced by the Structural Engineering Association of California (SEAOC) recommendations.

• These recommendations have been adopted and embraced by many code developing agencies and organizations such as the National Earthquake Hazard Reduction Program (NEHRP), and later the International Building Code (ICC2000).

• These codes had influenced many codes around the world. Other codes that have influenced are the Building Standard Law of Japan; Eurocode7and New Zealand Building Standard Law.

• The above mentioned codes are predominately prescriptive codes which specify minimum strength and stiffness for structural members. There are new emerging Performance-Based Design (PBD) codes that have different philosophy than that of the prescriptive ones. Performance-based design codes permit the designer to meet certain standard performance objectives, independent of meeting the prescriptive strength and stiffness criteria. In other words quantifiable levels of damage for specified levels of hazard are permitted.


Earthquake Resistant Design Provisions

• To design buildings to resist earthquake forces, several factors must be considered. Such factors can be divided into the following five categories:

• seismological factors such as seismic zone on which the structure is to be constructed

• geotechnical factors such as soil type, soil profile, soil dynamic properties and its liquefaction potential

• structural factors such as lateral force resisting systems and dynamic properties of the buildings

• architectural factors such as building shape and form • social factors such as building occupancy importance.


Analysis Methods• To include the earthquake ground motion effect,

buildings can be analyzed using different static and dynamic methods. Such methods include:

• Equivalent static method• Response spectrum method• Time history method• Push-over method. • For low and medium rise regular buildings in low

and moderate seismic activity zones, the equivalent static method has been adopted predominately by almost all building codes. The equivalent static method formula is very much a function of similar factors.


Equivalent Static Method• The most widely used equivalent static method

formula is that of the Uniform Building Code (UBC-94) adopted from SEAOC. This formula is the basis of most formulas found in other codes and it will be adopted here. The equivalent static method calculates the lateral seismic base shear which is a function of the factors mentioned above. The base shear in a building can be calculated using the following formula (UBC-94):

• W

R

ZICV

w

where:Z = Seismic zone factor; I = Importance factor; W = Weight of the building, total

dead load and a percentage of live load; Rw = Numerical seismic coefficient (Response Modification Factor); C = Numerical coefficient determined.


Siesmic Hazard Assessment

• Seismic hazard zoning studies were conducted for different countries of the Arabian Peninsula

• The eastern portion of the Arabian Peninsula (UAE, Qatar, Bahrain, Kuwait, Northern Oman) were excluded from previous SHA studies

• Some extrapolated result shows hazard levels of almost 0.5g at the northern most part of the UAE. This result is very high and unrealistic.

• This study is intended to include UAE and its surrounding areas and improves on previous extrapolated SHA result.


Seismic hazard assessment• There are two prevalent methods for seismic

hazard analysis; the deterministic approach and the probabilistic approach

• The probabilistic approach, used in this investigation, takes into account the uncertainties in the level of magnitude of earthquake, its hypocentral location, its recurrence relation and its attenuation relation


Steps of the Probabilistic Seismic Hazard

The steps for seismic hazard assessment can be summarized as follows:

(1) Modeling of seismic source regions; (2) Evaluation of recurrence relation, i.e., frequency-

magnitude relation; (3) Evaluation of attenuation laws for intensity or peak

ground acceleration; (4) Evaluation of activity rate for earthquake-probability of

occurrence; (5) Evaluation of basic parameters such as lower and upper

bound for earthquake magnitude and distribution of seismic events and

(6) Evaluation of local site effects such as soil type, geotechnical characteristics of sediments, topographic effects, etc.


Modeling of seismic source regions

The seismic source regions are:• Source Region I: Main Zagros Thrust Region. • Source Region II: North East Arabian Gulf Region. • Source Region III: Northern Emirates Region • Source Region IV: Lut Region • Source Region V: Central Iran Region.• Source Region VI: Makran Region. • Source Region VII: South East Arabian Gulf

Region


Seismic source regions of UAE and its surrounding

(for M≥4 from 1964-2002 and for M≥6 from 1900-1964)

Bahrain

Qatar

Region IRegion II

Region III

Region VII

Gulf of Oman


Region V

Region IV

Region VI

50.0 0 51.0 0 52.0 0 53.0 0 54.0 0 55.0 0 56.0 0 57.0 0 58.0 0 59.0 0 60.0 0

Eas t L ongitude

20.0 0

21.0 0

22.0 0

23.0 0

24.0 0

25.0 0

26.0 0

27.0 0

28.0 0

29.0 0

30.0 0N

orth

Lat

itude



Iran


Recurrence and Attenuation Relations

• Gutenberg and Richter had devised this logarithmic relationship (G-R formula) for seismic hazard analysis

• An attenuation relation that resulted from calibration and adjustment of constants to reflect the region characteristics such as transmission path, soil type, source, etc., developed by IIEES [Zare, 2002] is used in the current study. The general form of the attenuation equation is in the following form:

log N a bM

PScRRCMCa ii )(loglog 21 Gulf Seismic Forum 2005


Seismic Hazard Parameters

wM

Source Region No.

Total No. ofEvents

(N)

MinimumMagnitude

MaximumMagnitude

b-Values a-Values

I 866 4.0 7.0 1.22 10.17

II 106 4.0 6.0 0.94 6.99

III 30 4.0 6.0 0.70 5.22

IV 369 4.0 6.8 1.11 9.01

V 140 4.0 7.2 0.89 7.34

VI 6 4.0 6.7 0.35 2.74

VII 29 4.0 7.5 0.57 4.88

wM


Seismic Hazard Results

• Seismic Hazard Analysis for three time spans has been conducted

• Mainly, 50, 100 and 200 years

• Seismic zone map for 475 years return period is generated


PGA ( ) for 50 years time span

Bahrain


Gulf of Oman


5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00N

orth

Lat

itude

Qatar

Iran


cm / sec2



cm / sec2

Bahrain

Qatar


Iran


Gulf of Oman


5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00

Nor

th L

atitu

de



cm / sec2

Bahrain

Qatar


Iran


Gulf of Oman


5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00N

orth

Lat

itude


Summary of PGA (in g) with a 10% probability of being exceeded in time span

Regions Source Name 50 Years 100 Years 200 Years

I Main Zagros Thrust Region 0.30 0.40 0.51

II North East Arabian Gulf Region 0.24 0.32 0.41

III Northern Emirates Region 0.22 0.30 0.38

IV Lut Region 0.26 0.34 0.45

V Central Iran Region 0.25 0.33 0.43

VI Makran Region 0.19 0.26 0.34

VII South East Arabian Gulf Region 0.16 0.22 0.30


Seismic zoning map of UAE and its vicinity for 50 years period with 10% probability of being

exceeded

Zone 3

Bahrain

Qatar


Iran


Gulf of Oman


5 0.00 5 1.00 5 2.00 5 3.00 5 4.00 5 5.00 5 6.00 5 7.00 5 8.00 5 9.00 6 0.00

E ast Lon g itu de

2 0.00

2 1.00

2 2.00

2 3.00

2 4.00

2 5.00

2 6.00

2 7.00

2 8.00

2 9.00

3 0.00N

orth

Lat

itude

Zone 0

Zone 1

Zone 2A

Zone 2B


Seismic Zone factor (Z)

• The Z-value represents the maximum effective peak acceleration (EPA) and is expressed as a fraction of the gravitational acceleration, g. The peak ground acceleration (PGA) in Table 1 need to be adjusted to give the effective peak acceleration EPA. The results are listed below

Zone NumberPGA ( g) Z

0 Less than 0.05 0.05

1 0.05 - 0.1 0.08

2A 0.1 - 0.20 0.16


Seismic Zone Factor (Z)

Large parts of UAE, specifically Southern UAE, lies within Zone Zero Greater Abu Dhabi area lies within Zone 1. Fujaira, greater Dubai, Sharjah and Ajman area lies within Zone 2A. No part of UAE lies within Zone 2B or Zone 3.


Spectral Acceleration Coefficient (C)

• This coefficient is to account for the spectral amplification of ground motion based on structure fundamental period (T) and site response factor (S).

3

2

25.1

T

SC

The empirical formula for calculating fundamental period of vibration of buildings (in seconds) according to (UBC-94) is given by:

4

3

)( nt hCT


Other Factors I and Rw

• The importance factor, I, is determined based on the building importance and is used to provide for more conservative design for important facilities. The importance factor ranges from 1.0 for single family dwellings to 1.5 for building needed immediately after earthquake such hospitals, power stations and the like.

• The response modification factor, Rw, is introduced to account for the reduction in structural response caused by damping of the structure and its inelastic response. The response modification factor ranges from 5 for masonry bearing wall system to 12 for dual systems with special-moment-resisting frame.


Acceleration Time History Recorded at

AUS Station in Masafi, December 2002

0 1 2 3 4 5 6 7-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

Time (s)

Accele

ration (

g)


Acceleration Response Spectra (AUS

Station in Masafi, December 2002)


Conclusions and Future Work• Three major elements of an earthquake design code, mainly seismic zoning,

dynamic characteristics of common types of buildings and design response spectra were addressed in details and some recommendations were made. However, there are several factors that need to be specialized for UAE. In order to do so the following miles stones need to be achieved

• Evaluation of relationship between buildings types, their width, their height and their fundamental period of vibration (T).

• Determination of local site effect (S) and soil parameters for the common types of soils in UAE for amplification or attenuation of ground motion.

• Development of design response spectra for areas of critical structures.• Evaluation of response modification factor (Rw) for buildings.• Evaluation of importance factors for buildings (I), elements, components and

equipments.• Development of attenuation relationships for UAE to fine tune the seismic

hazard map developed based on Zagros attenuation relation.• Study of the liquefaction potential of the different types of soils of UAE.• Installation of strong motion recorders (Seismometers) to record strong

ground motion in different parts of the country and in major installations.• Instrumentation of critical and historical buildings and monitoring of their

response.• Study earthquake codes of surrounding countries.


Acknowledgment

The support for the research presented in

this paper had been provided by the

American University of Sharjah, Faculty

Research Grant. The support is gratefully

acknowledged. The views and conclusions

are those of the author and should not be

taken as those of the sponsor.


Thank You

• ATC-19: This report , Structural Response Modification Factors, was funded by NSF and NCEER. The report addresses structural response modification factors (R factors), which are used to divide seismic forces that would be associated with elastic response to obtain design force levels. Available through the ATC office. (Published 1995, 70 pages)

• Abstract: The report documents the basis for current R values; how R factors are used for seismic design in other countries: a rational means for decomposing R into key components, a framework (and methods) for evaluating the key components of R, and the research necessary to improve the reliability of engineered construction designed using R factors.

Earthquake catalogue of UAE• There are several catalogs available for the region

of interest. These mainly include: The National Earthquake Information Center (NEIC), International Seismological Center (ISC), International Institute of Earthquake Engineering and Seismology (IIEES), British Geological Survey (BGS), National Oceanic and Atmospheric Administration (NOAA) and others

• The IIEES catalog (Farahbod and Arkhani, 2002) is adopted and supplemented with additional events covering the region under study

Conclusion• The significant results of this investigation are: • review of tectonics and seismotectonics of the studied area• generation of seismic zone map that can be used, however with caution,

as a guide for determining the design earthquake and Z factor.• Generation of the C factor which is a function of T and S

• Limitations are: • The hazard assessment is done for an ideal bed-rock condition,

therefore care should be taken when using the results for sites with special local conditions. In such cases, evaluation of local site effects should be considered for microzonation of mega cities (S factor).

• The attenuation relation used in this investigation is for Zagros fold zone. Attenuation relations for the region should be developed when sufficient strong motion data become available.

• The I, Rw, and C factors need more work

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