introduction to earthquake engineering - universität kassel introduction to earthquake engineering...

Introduction to Earthquake Engineering

Seismic Risk Assessment

Prof. Dr.-Ing. Uwe E. Dorka

Risk is a function of:

• Hazard • Vulnerability • Loss

2

Definition of risk

Uwe E. Dorka: Seismic Risk Asessment

• Ground shaking

Uwe E. Dorka: Seismic Risk Asessment 3

M 6.4 2016 Southern Taiwan Earthquake

Seismic hazard sequel NARlabs report Taiwan

• Ground shaking • Land slide


M 7.0 2016 Kumamoto Earthquake

Seismic hazard sequel

EERI virtual clearing house

• Ground shaking • Land slide • Liquefaction


M 7.5 1964 Niigata Earthquake

Seismic hazard sequel EERI slide collection

• Ground shaking • Land slides • Liquefaction • Fires


M 6.9 1995 Kobe Earthquake

Seismic hazard sequel EERI slide collection

• Ground shaking • Land slides • Liquefaction • Fires • Tsunami


M 9.0 2011 Tohoku Earthquake

Seismic hazard sequel EERI clearing house


Seismic hazard sequel

Each “risk element” (building, bridge, factory, shopping mal etc.) has an individual seismic hazard sequel, which depends on its location and the tectonic scenario that needs to be considered

This leads to: Damage Loss


The Osaka Bay seismic hazard scenario

The Osaka Bay scenario considers a rupture of the Nankai Trough generating a M9.1 earthquake and tsunami comparable to the 2011 Tohoku event

From: http://www.bousai.go.jp/jishin/nankai/nankaitrough_info.html


Intensities will be high, especially in coastal regions (JMA 7 = MM 10 – 11) throughout Japan.




For Osaka, Intensities are smaller (JMA 6 = MM 8) but widespread liquefaction must be expected.




The expected tsunami is large: It will inundate a large part of Osaka city, requiring evacuation of about half of the population living in the inundated areas necessary within 30 min.




Landslides are not a problem for Osaka, but in the surrounding mountains and on the other side of the bay in Kobe. Studies on post-quake fires are not in the reports!



Vulnerability assessment

• Structures • Transport (roads, rail road, water ways) • Other life lines (fresh water, sewage, electricity, gas, communication) • Industrial facilities (production) • Commercial facilities (malls, banks, warehouses etc.) • Secondary elements (building contents, equipment, goods, etc.)

A number of “risk elements” can cause losses due to their seismic vulnerabilities, among them are:

Vulnerability assessment is the most critical and most complex task in seismic risk assessment!

It is also the least developed because it lacks realistic and validated methods!


Vulnerability assessment: Structures

Seismic codes are not “codes of practice” as they should be: Buildings are not built that way and don’t behave that way: Code conforming calculation: •Düzce and Kocaeli buildings •Düzce event

1999 Düzce damage data base: •484 rc-frame structures, •1-7 storeys

(from Ref 1)



Seismic codes are not “codes of practice” as they should be: Buildings are not built that way and don’t behave that way: Code conforming calculation: •Düzce and Kocaeli buildings •Düzce event

1999 Düzce damage data base: •484 rc-frame structures, •1-7 storeys

(from Ref 1)



• Structural regularity is largely a myth: Soft storeys are everywhere

Seismic codes are not “codes of practice” as they should be: Buildings are not built that way and don’t behave that way:




• Floor levels are not aligned





• Floor levels are not aligned • Corner buildings are pushed out





• Floor levels are not aligned • Corner buildings are pushed out • Workmanship: In most regions the

necessary skills are missing





• Floor levels are not aligned • Corner buildings are pushed out • Workmanship: In most regions the

necessary skills are missing • Quality control requirements are

unrealistic




Seismic codes are not “codes of practice” as they should be: Buildings are not built that way and don’t behave that way: • Structural regularity is largely a

myth: Soft storeys are everywhere • Floor levels are not aligned • Corner buildings are pushed out • Workmanship: In most regions the

necessary skills are missing • Quality control requirements are

unrealistic • Engineers have to use design

methods that don’t reflect actual limit states



The best possibility for structural vulnerability assessment: A database with buildings that suffered earthquake damage! Düzce damage data base: •1999 Düzce event, Mw = 7.2 •484 rc-frame buildings investigated •1-7 storeys •Typical for 90 % of buildings in Turkey



The next best possibility for structural assessment: A virtual building database! Can be created by the SBP Tool through fuzzy criteria: • Dimensions of ground plan,

windows and doors • Number of storeys • Balcony • soft storey • etc.

(from Ref 5)



The next best possibility for structural assessment: A virtual database! A virtual city ward: • Number of buildings: 100 • Number of nodes: 505.347 • Number of finite elements:

304.157 • Number of DOF: 1,676,754 • Duration for running a time

history with 1.500 Time steps (by using OpenHySL): 4,5 hours

(from Ref 5)

Needs realistic local mechanical modelling. This information is still missing!


Vulnerability assessment: Life lines

• Transport: Roads, rail roads, water ways • Water: Fresh water, sewage systems • Energy: Electricity, oil, gas • Communication: Computer nodes,

satellite links


Vulnerability assessment: secondary “risk elements”

• Building contents: windows and doors, water-, electrical- and heating systems, furniture, household items, etc.

• Equipment: Vehicles, machines, appliances, computers, etc.

• Stored goods: foods, garments, spare parts, appliances, etc.


Loss assessment:

There is a distinction between human and economic losses!

Economic losses can be valued. They are separated into: •Direct losses are losses directly related to damage or destruction of “risk elements”, e.g. repair or replacement costs of bridges, dams, buildings, their contents, equipment, stored goods, etc. •Consequential losses are indirect losses, e.g. business interruptions, loss of jobs, increase in health care costs, event cancellations (rock concerts) etc. This is the realm of insurance companies. Their approach requires a loss data base (not just damage data base!)

Human losses (deaths, injuries) need immediate attention. Their assessment is needed for an effective emergency planning and response.


Economic loss assessment

Insurance concept for earthquake loss estimation of large portfolios

(after Ref 4)

Loss functions

Value distribution

Hazard representation



Hazard Zonation: Probabilistic seismic hazard maps based on return periods

(from Ref 4)



Or scenarios: Probability of occurrence of extreme events in an area

(from Ref 4)



Exposure Zonation: The CRESTA Format

(from Ref 4)



Loss calculation: • Generation of large sets of synthetic events from hazard representation • Calculation of losses for each event using regional value distribution (CRESTA)

and loss functions (loss data base for risk elements) • Sort results by losses and cumulate event probabilities

Losses vs. hazard probability (PML Chart)

(from Ref 4)



PML Chart to identify the probable maximum loss (PML) and calculate the average annual loss (AAL) for a portfolio.

(NatCat calculation, Munich Re, Ref 4)



Portfolio vs. single risk: • A portfolio contains a large

number of risk elements distributed over a large area. Single, even extreme events have no significant effect on the expected losses: Probabilistic assessment

preferred. • For a single risk, extreme

events are significant for loss estimation: Scenario based

assessment preferred.

portfolio

single risk

Return period

Loss

in %

of T

SI

(from Ref 4)

• Probabilistic ground motion assessment is well developed • Extreme event studies are now done, but are still in an infant stage • A hazards sequel needs to be considered for any “risk elements”

• Vulnerability assessment is grossly underdeveloped but is key to realistic seismic risk assessment!

• Realistic virtual damage databases are needed for various risk elements (but in particular structures!) to calculate realistic loss data

• This requires a coordinated world effort of large-scale experiments to validate detailed numerical models, especially of structures

• Or we wait until one of our large urban centres is destroyed by an extreme event, which is sure to come!


Current status of seismic risk assessment

1. Berth (2013). Simulated seismic vulnerability based on nonlinear SDOF building models vs. observed damage for residential buildings in Turkey, Master Thesis, Universität Kassel

2. EERI Slide collections 3. Japan Cabinet Office (2012). Nankai Trough Earthquake Damage

Information. Available from: <http://www.bousai.go.jp/jishin/nankai/nankaitrough_info.html>. [1 October 2013].

4. Hollnack (2010): Earthquake Risk Modelling, Lecture material, Munich Re.

5. Mühlhausen, Dorka (2016). Seismic risk simulation using a virtual data base. Workshop presentation, Universität Kassel


References

introduction to earthquake engineering - universität kassel introduction to earthquake engineering...

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