Seminar on

Earthquake Resilient Design for School Buildings

Naveed Anwar, PhD

Post-earthquake School Reconstruction Project

Seismic Risk and PerformanceDay-1Session 1

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•Earthquakes cause disasters!• Why do they cause disasters?

• Understanding the Risk

•Can such disasters be minimized?• How can we reduce the consequences of such disasters

• Understanding the Response and Performance

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Seismic Risk and Performance

Understanding the nature and

source of earthquakes

Understanding Risk they pose

Understanding Performance required

from structures to reduce the risk to acceptable level

Why do Earthquake Cause Disasters?

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What is a disaster

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Climate Change

Environmental Sustainability

Population Growth

Urbanization and Un-planned

development

Low Quality of Built Environment

Lack of Resources for Communities

Lack of post-event management and recovery, and re-bound capacity

Natural Phenomena

Disaster Hazard Exposure Vulnerability

Increased Consequences

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Seismic Risk

Seismic Risk = Seismic Hazard x Seismic Vulnerability

What is Seismic Hazard

10Source: Murty (2004)

For Hazard

Earthquake

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Arrival of Seismic Waves at a Site

Source: Murty (2004)

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Reducing illumination with distancefrom an electric bulb

Effected by “Medium in between”

Clear, FogReflection, Abortion

Source: Murty (2004)

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Seismic hazard Maps

Seismic hazard map of Asia, from the Global Seismic Hazard Assessment Program (GSHAP)

http://www.seismo.ethz.ch/static/gshap/

What is Earthquake and its causes

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Where do earthquakes occur ?

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Tectonic Plates

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Tectonic Plates

Theory of Continental Drift

18The Indian Plate is moving north into the Eurasian Plate

Source of Earthquakes in Nepal

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History : First recorded Earthquake

• A violent earthquake struck on June 7, 1255 AD.

• The earthquake toppled many houses and temples.

• It killed 30% of the population of Kathmandu, including King Abhaya Malla.

• The magnitude of the earthquake is said to be around 7.7 in Richter scale.

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How is Seismic Hazard measured

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Measuring Seismic Hazard

• Based on Magnitude (Energy released)• Richter scale (1 to 10)

• Based on Intensity of shaking• Modified Marcelle (MM) scale (1 to 12)

• Based on ground movement characteristics• Ground acceleration (fraction of g)

• Based on Response to ground shaking• Response acceleration (short and long period)

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Earthquake Magnitude

• The magnitude is a number that characterizes the relative size of an earthquake.

• Magnitude is based on measurement of the maximum motion recorded by a seismograph. • local magnitude (ML), commonly referred to as "Richter magnitude“

• surface-wave magnitude (Ms

• body-wave magnitude (Mb

• moment magnitude (Mw)

• Scales 1-3 have limited range and applicability. The moment magnitude (Mw) scale, based on the concept of seismic moment, is uniformly applicable to all sizes of earthquakes

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Seismic hazard Zones (NBC 105:1994)

90% Nepal’s land area underModerate-to-Severe Seismic Hazard

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Seismic hazard map of Nepal showing peak ground acceleration (PGA) on bedrock in gals for 500 years return period

(Wijeyewickrema et al. 2011).

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Using Response levels as indicator of Hazard

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Using Response Spectrums as Measure of Hazard

• Adjust Maximum Considered Earthquake (MCE) values of Ssand S1 for local site effects• SMs = Fa x Ss• SM1 = Fv x S1

• Calculate the spectral design values• SDS = 2/3 x SMS• SD1 = 2/3 x SM1

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Using Levels of Earthquakes

Terminology used to define earthquake

Maximum Credible Earthquake (MCE)

Maximum Design Earthquake (MDE)

Safe Shutdown Earthquake (SSE)

Contingency Level Earthquake (CLE)

Ductility Level Earthquake (DLE)

Operating Basis Earthquake (OBE)

Maximum Probable Earthquake (MPE)

Strength Level Earthquake (SLE)

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Maximum Credible Earthquake (MCE)

• Earthquake associated with specific seismotectonic structures, source areas or provinces that would cause the most severe vibratory ground motion or foundation dislocation capable of being produced at the site under the currently known tectonic framework

• Determined by judgment based on all known regional and local geological and seismological data

• Little regard is given to its probability of occurrence, which may vary from less than a hundred to several tens of thousands of years

What is vulnerability

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Seismic Vulnerability

• The weaknesses in the location and structure that will be exploited by the earthquakes

• Site Vulnerability• Soil type and profile that may amplify the hazard

• Structural Vulnerability• The factors that will increase the seismic demands and or reduce capacity

What is exposure

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Exposure to Seismic Hazard

• The people, property, assets, infrastructure that could be effected by the damage caused by earthquake

• No exposure > No disaster• Earthquake in a desert causes no disaster• Same earthquake in a crowded city is disastrous• Unoccupied building has no exposure to life, but exposure to assets still

present

• Nepal Earthquake of 2015 less disastorus due to reduced exposure• Schools closed• Day time, on a holiday

How can we reduce Consequences of Earthquake?

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What needs to be Done

Minimize Disaster Consequences

Reduce Risk to Disaster(and manage consequences due to disaster)

Reduce Vulnerability to match Acceptable Risk

Define Acceptable Risk

Determine the Hazard

(R = V x H)

Difficult to reduce Hazard

Difficult to reduce Exposure

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Nepal is exposed to High Seismic risk

Risk = Vulnerability X Hazard

Consequences - Disaster

(Death-Dollars-Downtime)

High Vulnerability High HazardHigh Risk

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Hazard-Vulnerability-Risk-Consequences

Structural Displacement

Load

ing

Seve

rity

Resta

urant

Resta

urant

Resta

urant

Haz

ard

Vulnerability

Consequences

School

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Restaurant Restaurant

Resta

uran

t

Operational (O) Immediate Occupancy (IO) Life Safety (LS) Collapse Prevention (CP)

0 % Damage or Loss 99 %

Ref: FEMA 451 B

CasualtiesLowest Highest

Rehab Cost to Restore after eventLowest Highest

Downtime for RehabLowest Highest

School School

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Progression of Structural Design

Limits on the allowable stresses to achieve in-direct FOS

Explicit consideration of partial FOS.

Formulation of limit state design principles.

Formulation of ultimate strength.

The recognition of the difference between brittle and ductile failure.

The introduction of capacity based design approaches.

Performance based design and more explicit linkage between demand and performance.

Risk integrated based design, and a more and holistic approach towards consequence based engineering.

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Seismic Design Approaches

Code Based Design

Performance Based Seismic Design

Consequences and Risk Based Design

Resilience Based Design

How do structures respond to Earthquakes

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Earthquake effects are Different

• Earthquake is different from all other loads• It is not an applied external force

• Earthquake effects are generated by the structure itself in response to ground shaking• Basically depends on stiffness and mass distribution

• Can be controlled by damping, ductility and energy dissipation mechanisms

4343

Concept of 100% g (1g)

Most loads

Earthquake

FFKuuCuM NL

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Earthquake Inertial Forces

Source: Murty, (2004)

Effect of Inertia in a building when

shaken at its base

Flow of seismic inertia forces

through all structural

components

Inertia force and

relative motion within a

building

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Building Behavior during Earthquakes

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Schematic Representation of Seismic Forces

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Response Depends on the Structure and Soil

Different Buildings Respond Differently to Same Ground Vibration

Source: Murty (2004)

Vulnerabilities in Structures

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Typical Vulnerabilities

• Irregularity of mass and stiffness

• Lack of stiffness

• Lack of strength

• Lack of ductility

• Weak failure mechanisms

• Lack of damping

• Lack of Stability

• Lack of energy dissipation mechanisms

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Buildings have unequal vertical members;

they cause the building to twist about a

vertical axis

Source: Murty (2004)

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Sudden deviations in load transfer path along the height lead to poor

performance of buildings.

Source: Murty (2004)

How can we reduce vulnerability

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Basic approaches

• Systematically check and remove the vulnerabilities• During Basic Planning

• During Structural System

• During Structural Design

• During Structural Detailing

• During Construction

• During maintenance

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Plan shapes of buildings

Preferable Not Preferable

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Simple plan shape buildings do well during earthquakes

Source: Murty (2004)

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Buildings with one of their overall sizes much larger or much smaller than the other two, do not perform well during earthquakes

Source: Murty (2004)

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Identical vertical members placed uniformly in plan of building cause all points on the floor to move by the same amount.

Source: Murty (2004)

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Vertical members of buildings that

move more horizontally sustain

more damagePounding can occur between

adjoining buildings due to

horizontal vibrations of the twobuildings

Source: Murty (2004)

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Open ground storey building - assumptions made in current design practice are

not consistent with the actual structure.

Source: Murty (2004)

How can we measure and control response

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Determining Response and Controlling it

• Use proper models

• Use proper hazard estimation

• Use appropriate analysis techniques

• Determine key response indicators

• Check response indicators against prescribed limits

• Modify structural properties to reduce demand or increase capacity

• Generally conform to building codes and guidelines

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Next Presentations

• Design Criteria for establishing what is to be done and how design is to be carried out

• Structural Analysis and Design to determine response and control it for new buildings

• Retrofitting to improve structures that have already been built

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Useful Reference

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