Current Situation and Future Development of Earthquake Countermeasures for Structures in Sri Lanka by Eng. K.L.S. Sahabandu,

Knowledge and Experience Sharing Seminar on Disaster Management

Current Situation and Future Development of Earthquake Countermeasures for Structures in Sri Lanka

Eng. K.L.S. Sahabandu, DMC, Sri Lanka 1

Current Situation and Future Development of Earthquake Countermeasures for Structures in

Sri Lanka

Eng. K.L.S. SahabanduChairman

Sub-committee on Developing Building Guidelines for Earthquake Resistant DesignsDisaster Management Centre

Sri Lanka

Outline

IntroductionSeismic MonitoringCurrent Practices for Earthquake Resistant StructuresPreparedness for Earthquakes

Introduction

• Sri Lanka had been considered to be in an aseismiczone being located away from major plate boundariesor any active faults.

• However, recent seismic events in the region andoccurrence of few minor earth tremors have reformedthis thinking.

• In the mean time, recent geological studies show thatthere is a possibility of forming of new plateboundary approximately 500 km-700 km south of SriLanka in the middle of Indo-Australian tectonic plate.

• Therefore, Sri Lanka can no longer be consideredisolated from the effects of seismic activities.

New Plate Boundary Belief

Introduction (contd..)

• The first documented earthquake in Sri Lanka occurred in1615 AD and had an estimated magnitude of 6.5 on theRichter scale. This earthquake killed thousands of people anddestroyed hundreds of houses in Colombo. In the recent pastwe have experienced many earth tremors but no majordamages to structures were reported.

• Since then about 100 earth tremors have been reported in andaround Sri Lanka.

• Any future earthquake close to a city centre such as Colombowill have disastrous consequences due to its presentdevelopment and population. Therefore, we have understoodthe necessity to study the seismic effects on Sri Lanka andtake appropriate action to mitigate the same.

Record of earthquakes (M>=5) in the region from 1505 toMarch 2010, by Indian Metrological Department




Earthquake Effects on Sri Lanka

Mainly two earthquakes which happened inIndonesia in recent past considerably affected theSri Lankans.

Earthquake occurred on 26th December 2004,caused huge damage due to Tsunami effectcaused huge damage due to Tsunami effect.

Tsunami waves reached the Eastern and Southerncoasts of Sri Lanka two hours later the initialearthquake and killed over 35,000 people anddestroyed approximately 100,000 houses.However, earthquake tremor was not felt by SriLankans on 2004, while tsunami created a hugedamage.

Earthquake Effects on Sri Lanka (Contd…)

The next considerable effect of earthquakehappened on 11th April 2012. Though the epicenterof this earthquake was located at Indonesia whichis more than 1600 km away from Sri Lanka, it wasfelt by Sri Lankans at many parts of the countryy y p y(Even in Central Highland)

According to the reported data, many people feltshaking of their households and some complainedthat their houses (mainly at Diyatalawa, Jaffna andMannar) had cracked.

Seismic Monitoring in Sri Lanka Sri Lanka

Except for micro-seismic activities monitored at Kotmale andVictoria reservoirs (after impounding of the reservoirs) hardlyany seismic monitoring was carried out in Sri Lanka till 2003. Atthe time of Tsunami in 2004 there was only one seismographoperating in Sri Lanka at Peradeniya.

Since then Geological Surveying and Mines Bureau (GSMB) has installed seismograph network to monitor inter-plate and intra-plate seismic activities around Sri Lanka at three locations Mahakandarawa, Hakmana and Pallekelle.

Seismic Monitoring in Sri Lanka (Cont…)

MALK

GEOFON Stations

GSN Stations

PALK

HALK

Seismic Monitoring in Sri Lanka (Cont..)

With the new system in seismic monitoring it is possible to:

Give early warnings to avoid the possibilities ford t ti d t t l di t i il t h t S idevastation due to natural disasters similar to what SriLankans have experienced in the recent Tsunami event.

understand the micro-seismic events and tectonicbehaviors using the available data from the system.

Current Practices for Earthquake Resistant Designs

Dams and Ancillary Structures

Buildings




Dams and Ancillary Structures

BackgroundDams in Sri Lanka can be categorized according to age and construction material / technology, (i.e. ancient dams, recent dams and modern dams.)

• Large and medium dams……………………...…...351 Small dams………………………………….…....12,000

• Ancient dams (Large & Medium) built centuries ago but restored from 1850 AD onwards…………..300

• Recent dams built within past 100 years…..…...…..35• Modern dams built within last 30 years………..…....15

Dams and Ancillary Structures (Cont...)

• Medium and Large -351Earth dams - 339Concrete gravity - 07C t d/ h 01

14

Concrete d/ arch - 01Rockfill - 04

• Small 12,000

Large Dams according to ICOLD classifications - 80

NEED FOR EARTHQUAKE RESISTANT DESIGNS FOR DAMS

Causes of devastation could be due to earthquake action and subsequent release of massive amount of water.

Collapse of a dam or ancillary structure may lead to a progressive and catastrophic failure releasing a massive volume of water which could devastate the properties and loss of human lives in downstream areas.

15

• Earth Mass of Landslides falling into the reservoir.

Defects in dam body foundation and auxiliary structures

Likely Damages to Reservoirs during Earthquakes

• Defects in dam body, foundation, and auxiliary structures leading to progressive or sudden failures.

16

Hydraulic Structures Designed for Earthquakes in Sri Lanka (History)

• Designing of Sri Lankan dams for earthquake loadingsbegan only in Nineteen Eighties (1980 AD) during theAccelerated Mahaweli Project.

• Important structures of Victoria, Randenigala, Kotmale, andRantembe Reservoir Projects were designed for seismiceffects.

• This trend continued after the Mahaweli Project and mainstructures of Samanalawewa and Kukule ReservoirProjects were also designed for seismic effects.

17

DESIGN METHOD AND CRITERIA

DESIGN ENVIRONMENT : ASEISMIC

EARTHQUAKE EFFECTS : CALCULATED ACCORDING TO THE “PSEUDO-STATIC METHOD”PSEUDO STATIC METHOD

HORIZONTAL GROUND ACCELERATION : ASSUMED

VERTICAL ACCELERATION : ASSUMED

18




ASSUMED VALUES FOR ACCELARATION COEFFICIENTS

Reservoir Project Horizontal Acceleration Coefficient

Vertical Acceleration Coefficient

VictoriaRandenigala 0.1g 0.0Kotmale 0.08g 0.005gRantembe 0.1g 0.0SamanalawewaKukule 0.05g 0.0Upper Kotmale 0.1g / 0.05g 0.0

19

PSEUDO-STATIC METHOD

THREE TYPES OF EFFECTS CONSIDERED

• INERTIA EFFECTSeismic Acceleration Coefficient x Mass

• HYDROSEISMICAL PRESSURE EFFECTCalculated according to the Westergaad Formula

• EARTH PRESSURE EFFECTCalculated according to the Monobe-Coulomb Formula

20

INERTIA EFFECT

Horizontal Force = Seismic Coefficient (0.1) x g x Mass

W.T.H1 = 0.1g x γ(bulk) x Volume (ABCD)

A B

C D

21

H1 = 0.1g x γ(sub.) x Volume (CDEF)

C D

E F

HYDROSEISMICAL PRESSURE EFFECT

Calculated according to Westergaad Formula

W T

W.T.Earthquake Acceleration

22

W.T.

zz

WESTERGAAD FORMULA

According to the Westergaard Formula increment of water pressure is given by

p = 7/8 . kH . gw .√(H . Z)Where

p = additional water pressure acting on one side (kN/ m2)kH = Seismic Coefficient (0.1)

gw = density of water (kN/m3)H = maximum water depth (m)z = distance from the free water surface to the point considered (m)

23

EARTH PRESSURE AT EARTHQUAKE

GROUND LEVEL

24

NORMAL EARTH PRESSURE

EARTH PRESSURE DUE TO EARTHQUAKE

H




EARTH PRESSURE AT EARTHQUAKE

Total Lateral earth pressure (static +dynamic) was computed by Monobe-Coulomb relationship.

aeae KHP 2

21 γ= )1).(cos(.cos

)(cos22

2

ηθβδββθφ

+++−−

=aeK;

25

)cos().cos()sin().sin(

βιθβδθφδφη

−++−−+

=i

where,

Kae = active earth pressure at earthquaketan θ = active earth pressure coefficientφ = angle of friction of soilδ = angle of wall frictionι = slope of ground surface behind wallβ = slope of the back of wall to vertical

LOADS AND FORCES

WAVE ACTIONPRESSURE DUE TO

14 kN/sq.mU/S WATER LEVEL

H1

D/S WATER LEVEL

Earthquake Acceleration

INERTIA FORCE, (Due to Earthquake Loading)

0.32

mZ

Zwγ

20 :

1

4 : 3

148.00

155.50

26

DISTRIBUTIONPRESSURE

HYDROSTATIC

(Due to Earthquake Loading)DISTRIBUTION

HYDROSEISMICALPRESSURE

HYDROSTATICPRESSURE

DISTRIBUTION

H2SELF WEIGHT

0.33

x γ

(H

1-H

2) +

γ H

2w

w

10 : 1

γ H

2


UPLIFT

w

1:10

5 : 1

134.00


HYDROSEISMICAL

Current Practice for Earthquake Resistant Buildings

Most common building types exist in Sri Lanka can bebroadly categorized as follows;

Non-engineered Buildings• Brick /Block Masonry load bearing wall housesBrick /Block Masonry load bearing wall houses• Wattle & daub houses

Engineered Buildings• Reinforced Concrete framed buildings• Reinforced Concrete framed buildings with masonry

infill• Multi-storied buildings with shear walls• Steel framed buildings

Current Practice for Earthquake Resistant Building Designs (Contd..)

• Until 2000 AD, engineered buildings were designed andconstructed without incorporating any earthquake resistantphilosophy / details.

• After 2000 AD, some of the engineered RC buildings havebeen designed and constructed incorporating earthquakeresistant philosophy / details as required by the investors.

Current Practice for Earthquake Resistant Building Designs (Contd….)

The current practice for RC Buildings can broadly becategorized into two;

General Approach for Ordinary Buildings (Seismic Mitigation pp y g ( gR/F Detailing)

Analytical Approach for Important / High-rise Structures (Combined with General Approach)


General Approach for Ordinary Buildings (SeismicMitigation R/F Detailing):

Adopting standard detailing practice to improve the ductility of the structural elements as per the “Manual for Reinforcement Detailing to Mitigate Seismic Effects” prepared by the Society of Structural Engineers, Sri Lanka.




General Approach for Ordinary Buildings (SeismicMitigation R/F Detailing) (Cont…)

General Approach for Ordinary Buildings(Seismic Mitigation R/F Detailing) (Cont…)

ANCHORAGE OF

General Approach for Ordinary Buildings (SeismicMitigation R/F Detailing) (Cont…)

ANCHORAGE OF STIRRUPS


Analytical Approach (Combined with General Approach):

In the case of important structures such as high-rise buildingsseismic loading as per available design codes of otherg p gcountries such as UBC 97, IS 1893 & AS 1704 are adopted instructural design using either,a) Equivalent Static Approachb) Dynamic Approach

This is only a stop-gap measure intended to fill the vacuum of appropriate standards to cater to the immediate need.

Preparedness for Earthquakes

It is not possible to prevent the occurrence of an earthquakesince it is a natural phenomenon.

However, damage can be minimized through preparedness.

During the last decade various entities both government andDuring the last decade various entities both government andnon-government have been engaged in this direction.

Presently, the Disaster Management Center (DMC) of SriLanka, which was established after 2004 tsunami, take thelead role in this endevour.

DMC is an apex body for the purpose of planning, co-coordinating and implementing strategies to mitigate certainnatural and other forms of disasters.

• No comprehensive studies have been carried out to developanalysis and design guidelines on earthquake resistant buildingdesigns in Sri Lanka as of now.

• There is a strong need thus to establish national buildingdesign guidelines for both engineered and non-engineeredbuildings to resist seismic loads

Preparedness for Earthquakes (Cont..)

buildings to resist seismic loads.

• Though initiations were made for the above after the tsunami of2004, the earthquake event occurred in Indonesia on 11th April2012 which was felt by many Sri Lankan solidified the aboveneed.

• Accordingly, a subcommittee was formed on 20th April 2012 byDMC to develop Building Guidelines for Earthquake ResistantDesigns.




Investigate seismic activities around Sri Lanka and todetermine characteristics of earthquakes which mayoccur in the future.


The Sub-committee on Earthquake Resistant Designs

Line of Action

Review of the current design practice which does notgenerally cater for seismic resistance.

Develop effective design process to mitigate theeffects of earthquake hazard in future.

National policy on earthquake resistant designs shallbe prepared based on scientific evidence.

Response spectrum at a point due to an “average earthquake” This requires the study of seismic observations made in the



Immediate Need

past in sites close to a the point and extrapolate/interpolatefrom such data. Lack of necessary data will lead us to assumean artificial earthquake based on regional/global knowhow.

• Seismic Hazard MapIt is necessary to prepare seismic zoning map indicating areasof probable maximum earthquake ground motion in terms ofpeak accelerations since it is not available at the moment.

1. Reviewing the seismic monitoring systems and proposeimprovement to the systems.

2. Developing Seismic Hazard Map including earthquakeintensities, acceleration coefficients, response spectrum,return periods etc.

3 D l t f 3D b f d l th t i th


The Sub-committee on Earthquake Resistant DesignsProposals

3. Development of a 3D sub-surface model that improves thesusceptibility of constructions against the possibleearthquake in Sri Lanka.

4. Development of national guidelines for seismic analysis anddesign of buildings (engineered) in Sri Lanka.

5. Development of national guidelines for seismic analysis anddesign of buildings (non-engineered) in Sri Lanka.

6. Improvement of the available Detailing Manual“Reinforcement Detailing for Mitigation of Seismic Effects”published by the Society of Structural Engineers, Sri Lanka.

7. Preparation of guidelines for Retrofitting Works.

Reviewing the seismic monitoring systems and proposeimprovement to the systems.

Objective:


Proposed Study 1


To establish a system of seismographs at populationcenters such as Colombo etc. and also at other placesof national importance to obtain response spectrum dueto a seismic event.

Developing Seismic Hazard Map

Objective:


Proposed Study 2


To build a conceptual model for seismic status of SriLanka considering inter-plate activity around it.To produce a seismic hazard zonation map for SriLanka with recommended bedrock responsespectrum/seismic coefficients for each zone.To propose further research projects (long-term) to beperformed to improve the accuracy of the map and toextend it to incorporate overburden response.

Development of a 3D sub-surface model

Objectives:


Proposed Study 3


To prepare a 3D model for subsurface layers inColombo area.To find out the relationship between the behavior of abuilding due to earthquake motion and underneath soilproperties.To find out the susceptibility to an earthquake or loadbearing according to the stratigraphy.




Development of national guidelines for seismic analysisand design of buildings (engineered) in Sri Lanka.

Objectives:To study and understand concepts analysis and


Proposed Study 4


To study and understand concepts, analysis anddesign criteria, guidelines used in other nations invarious part of the world.To develop performance based methodologies toanalyze and design buildings in Sri Lanka for possibleseismic effects.To check the significance of seismic loads on ourbuilding designs (low, medium and high-rise) by casestudies.

Development of national guidelines for seismic analysisand design of buildings (non-engineered) in Sri Lanka.

Objectives:


Proposed Study 5


To study and understand concepts, analyses anddesign criteria, guidelines and detailing used in othernations in various part of the world.

Preparation of guidelines based on above.

Improvement of the available Detailing Manual“Reinforcement Detailing for Mitigation of Seismic Effects”published by the Society of Structural Engineers, SriLanka


Proposed Study 6


Lanka.

Objectives:• Improve the details of existing manual to achieve the

better constructability and economy.

Preparation of guidelines for Retrofitting Works.

Objectives:To evaluate the condition of the existing buildings using


Proposed Study 7


To evaluate the condition of the existing buildings usingRapid Visual Screening Method outlined by FEMA.

To develop appropriate retrofitting techniques for varioustypes of buildings.

Thank you

Documents

Current Situation and Future Development of Earthquake Countermeasures for Structures in Sri Lanka by Eng. K.L.S. Sahabandu,