Seismic resilience of critical infrastructures and communities. Mexico’s experience after the September 2017 earthquakes. Lessons and opportunities.A Gustavo Ayala MiliánInstituto de Ingeniería, UNAM, MEXICO

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Scope of Presentation• BACKGROUND ON DISASTERS, • THE 2017 MEXICO CITY EARTHQUAKE EXPERIENCE • METHODS FOR THE SEISMIC EVALUATION AND DESIGN OF BUIDINGS• DISPLACEMENT‐BASED SEISMIC DESIGN OF BUILDINGS• EVOLUTION OF THE DISPLACEMENT‐BASED SEISMIC EVALUATION AND DESIGN OF BUIDINGS WITH A GENERAL RESILIENCE‐BASED METHOD

• GUIDELINES FOR RESILIENCE‐BASED SEISMIC DESIGN OF BUILDINGS• CLOSING REMARKS

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Terminology• Hazard: potential threat to people and the things they value; impact of an event on society and the environment. A  process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation.

• Disaster:  a singular large scale or large impact event that causes great damage and human suffering; overwhelms local capacity necessitating national or international assistance. A serious disruption  of the functioning of a community or a society at any scale due to hazardous events interacting with conditions of exposure, vulnerability and capacity, leading to one or more of the following: human, material, economic and environmental losses and impacts. 

• Disaster Risk:  The potential loss of life, injury, or destroyed or damaged assets which could occur to a system, society or a community in a specific period of time, determined probabilistically as a function of hazard, exposure, vulnerability and capacity.

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Metheorological disasters

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Atlántico desde  1851Pacífico desde    1949

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Metheorological disasters

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Seismological disasters

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100 YEARS OF EARTHQUAKES IN MEXICO

100 earthquakes per year with magnitudes > 4.5,

3 earthquakes per year with magnitudes > 6.0

1 earthquake > 7.5 every 5 years.

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Seismological disasters

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Event/Location Year M. # of Deaths

Deaths per Mil. Country

Deaths per Mil.Region

Michoacán/ Mexico city 1985 8.1 40,000?

Northridge/ Los Angeles, CA 1994 6.8 57 CA   1.8 14

Hanshin Awaji/Kobe, Japan 1995 7.2 5,500 47 3,600

Hur. Katrina/Nueva Orleans, Gulf Cost 2005 ‐‐‐ 1.970 Reg 1,640 N.O.   3,092

Wenchuan, China 2008 7.9 90,000 66 3,900

Port au Prince, Haiti 2010 7.0 316,000 32,250 100,000

Maule, Chile 2010 8.8 526 31 41

Christchurch, New Zeland 2011 6.3 184 46 74

Great Eastern/Tohoku, Japan 2011 9.0 19,000 148 3,300

Hur. Sandy/New York, New Jersey 2012 ‐‐‐ 120 2 state  3 15

Morelos Axochiapan/Mexico 2017 7.1 462

Courtesy from Mary Comerio 2019

High Casualties even where good Building Codes exist

Casualties

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Evento Location                        % GDP Estimatedlosses

Great Eastern Tohoku, Japan                        1‐4% $300,000 Mill

Hur. Katrina New Orleans/Gulf  0.1% $150,000 Mill

Wenchuan China                                     1‐3% $150,000 Mill

Hanshin Awaji Kobe, Japan $89,000 Mill

Hur. Sandy New York/New Jersey $60,000+ Mill

Christchurch New Zeland 20% $40,000 Mill

Maule Chile                                      18% $30,000 Mill

Northridge Los Angeles $26,000 Mill

Port au Prince Haiti                                     100% $12,000 Mill

Michoacán Mexico                              2.1‐2.4% %11,500 Mill 

Morelos Axo. Mexico $2,500 Mill  

Courtesy from Mary Comerio 2019

Losses

Low Loss Value ≠ Recovery Speed

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Event/Location Year Est. Years toRecover

Michoacán/ Mexico city 1985

Northridge/ Los Angeles, CA 1994 2‐4

Wenchuan, China 2008 3‐4

Maule, Chile 2010 4‐5

Hanshin Awaji/Kobe, Japan 1995 7‐10

Hur. Katrina/New Orleans, Gulf Cost 2005 5‐20

Christchurch, New Zeland 2011 10‐20

Great Eastern/Tohoku, Japan 2011 10‐20

Hur. Sandy/New York, New Jersey 2012 10‐20

Port au Prince, Haiti 2010 Decadas

Morelos Axochiapan/Mexico city 2017 ???

Cortesy fromMary Comerio 2019

Recovery

Recovery speed is slowed by disruption to complex urban systemsand proportion of the building type or system closed

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Sumary of the Impact

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total cost– 40,000 millions pesos, (est. $2 billion US Cy)

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Collapsed buildings

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Structural configuration Cases

Ground floor used as a shop or for parking 16

In‐plan and in‐height irregularities 6

Corner buildings 12

Flat slabs 7

Pounding 1

Falta de resistencia lateral y/o mantenimiento 10

Number of storeys 4 a 8 (26)1 a 3 (6)

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Example of damaged buildings

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Much has to be learnt from reviewing the reasons of structural damage:Soft/weak storeys Corner buildings

Flat slabs Lack of stiffness

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Force‐Based

Performance‐based

Consequenceand risk‐based

Energy‐ based

Resilience‐based

Seismic Design Approaches

Before 1908 Messina earthquake

Intuition‐based

After 1908

Seismic Design:Highly severe demandsFailure redefinedConstruction detailsBasic fundamentals only in last century

Current status: Two methodsForce‐based: analise response to a fictitious staticforce.Performance‐based: analise response to a target ferformance

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Performance-based approach

Two concepts, one method:• In seismic performance evaluation one knows (or thinks to know!) the 

design of the structure and aims to calculate its performance under a given seismic demand.

• In performance based seismic design one knows the desired performance and the seismic demand  of the structure and aims to obtain its design

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Performance-based seismic design

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Sao / Sa2Sa2 = (R/m)2 - (R/m)1

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Performance-based seismic design

Credits: Ron Hamburger

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Seismic design current vs. resilience-based

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• Broad Concept:– The capacity of a community to survive, adapt and  grow, no matter what kind of chronic stress or acute  shock they experience. Seismic resilience is defined as the ability of a structure to recover from the effects of an earthquake to its original functionality state in the shortest possible time and with a minimum cost

• Buzzword:– Every city, every government agency, every academic  wants to be seen “doing something about it”

• Components:– Research– Policy– Implementation

Resilience is the word of the day

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Seismic Resilience

• Seismic resilience considers community capabilities as they relate to effective preparation and mobilization before, during, and after an earthquake. 

• Structural design, on the other hand, is load dependent and does not consider recovery time. 

• Three words describe seismic resiliency: robustness, redundancy, and functionality recovery. Ultimately, blending robustness, redundancy and recovery characteristics will satisfy society objectives.

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Attributes of seismic resilience

Robustness: strength, or the ability of elements and systems to withstand a given level of demand without suffering degradation or loss of functionality; a robust design improves structural safety and collapse resistance against unforeseen and extreme demands.  A robust design protects a structure against hazards such as earthquakes by evaluating robustness indicators and designing for progressive collapse.Redundancy: the extent to which elements, systems, or other measures of analysis exist that are substitutable, i.e., capable of satisfying functional requirements in the event of disruption, degradation, or loss of functionality. A redundant building design can be expensive, but may be appropriate for critical systems. Functionality recovery: restoration of a specific system or set of systems to their “normal” level of functional performance. It isn't just about the building, it's about the people.

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The seismic resilience of a building can be achieved by reducing its probability of failure during an earthquake, as well as reducing the consequences from such failures and the time to recover functionality.

How to achieve a resilent system

Functio

nality

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How to calculate resilience

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Resilience-based seismic design

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Defined as a natural extension of the performance‐based approach, RBSD, in addition to guaranteeing performance, identifies and attempts to mitigate all threats that may hinder re‐occupancy and functionality objectives through enhanced design of both structural and non‐structural components, and pre‐disaster contingency planning.

Credits: ASCE 41-17

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The drift ratio, of a frame is defined as the ratio of the interstorey drift to the height of the storey, as (Priestley 1998):

Resilience-based seismic designInterstorey drifts on a plane frame

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Resilience‐based seismic design

Calculation of interstorey drifts

Plane frame subassemblage

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Concluding remarksThis presentation suggests building functionality as base future seismic design/evaluation methods.  There are various alternative questioning the usefulness of such approach suggesting alternative and more complex approaches.As profesionals we have to ask us: 1)WHO pays for the demolition of the buildings and the clean up of a city damaged by an earthquake?, 2) Are we properly communicating the risk to the stakeholders and the users of a building?, 3) Do we have to design for high levels of damage?, 4) Is it really more economical?, 5) Is it right that people cannot return to a their home/job?, 6) Do we want our city being destroyed by an earthquake.

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Epilog

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We, structural engineers, have a mission to make the world a better place to live.

Akira Wada

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Thank you!POR MI RAZA HABLARA EL ESPIRITÚ

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