Earthquake Risk Assessment of Structures. Dr. Carsten Block AGCS Expert Days, Munich

Size: px

Start display at page:

Download "Earthquake Risk Assessment of Structures. Dr. Carsten Block AGCS Expert Days, Munich"

Florence Glenn
6 years ago
Views:

1 Earthquake Risk Assessment of Structures Dr. Carsten Block AGCS Expert Days, Munich

2 Table of contents 1 Earthquake Risk 2 Damaging Effects of Earthquakes 3 Origin of Earthquakes / Terminology 4 Vulnerability 5 Design Objectives in Codes 6 Seismic Design and Construction Features 7 Assessment of Existing Buildings 2

Example Text Headline, second line of headline Body text, second line of body text Earthquake Risk = First bullet layer First bullet layer Headline, second line of headline Body text,

3 Example Text Headline, second line of headline Body text, second line of body text Earthquake Risk = First bullet layer First bullet layer Headline, second line of headline Body text, second line of body text First bullet layer First bullet layer - Second Hazard bullet layer x Vulnerability - Second bullet layer x Exposure - Second bullet layer - Second bullet layer 3

4 Seismic Risk Terminology Seismic Hazard is the probability that an earthquake will occur in a given geographic area, within a certain time and ground motion intensity. Vulnerability fragility or damageability, the relationship between hazard and damage, loss or disruption Risk The relationship between loss severity and frequency Exposure the buildings, contents, people and processes at risk Defining acceptable risk is difficult as it differs amongst Owners Engineers Government Agencies Insurance and Finance 4

5 Example Text Headline, second line of headline Body text, second line of body text Earthquake Risk = First bullet layer First bullet layer Headline, second line of headline Body text, second line of body text First bullet layer First bullet layer - Second Hazard bullet layer x Vulnerability - Second bullet layer x Exposure - Second bullet layer - Second bullet layer 5

effects - Fire - Flooding 1989 Loma Prieta Earthquake, USA J.

6 Damaging Effects of Earthquakes Ground Shaking Ground failure - Ground Displacement - Liquefaction - Landslides Indirect effects - Fire - Flooding 1989 Loma Prieta Earthquake, USA J.K. Nakata, United States Geological Survey 2010 Chile Earthquake 6

7 Damaging Effects of Earthquakes Ground Shaking Ground failure - Ground Displacement - Liquefaction - Landslides Indirect effects - Fire - Flooding 1995 Kobe Earthquake, Japan, Hanshin Highway 7

- Landslides Indirect effects - Fire - Flooding 1999

8 Damaging Effects of Earthquakes Ground Shaking Ground failure - Ground Displacement - Liquefaction - Landslides Indirect effects - Fire - Flooding 1999 Taiwan Earthquake 2007 Niigataken Chuetsu-oki Earthquake 8

effects - Fire - Flooding 1964 Niigata Earthquake, Japan

9 Damaging Effects of Earthquakes Ground Shaking Ground failure - Ground Displacement - Liquefaction - Landslides Indirect effects - Fire - Flooding 1964 Niigata Earthquake, Japan (photo courtesy of the University of Washington) 2010 Taiwan Earthquake 9

Indirect effects - Fire - Flooding 1995 Kobe Earthquake,

10 Damaging Effects of Earthquakes Ground Shaking Ground failure - Ground Displacement - Liquefaction - Landslides Indirect effects - Fire - Flooding 1995 Kobe Earthquake, Japan 1995 Kobe Earthquake, Japan 2011 Tohoku Earthquake, Japan 10

11 Origin of Earthquakes Earthquake A sudden, rapid shaking of the earth due to a release of energy in the earth s crust. Tectonic Earthquakes Volcanic earthquakes Collapse earthquakes (e.g. mining) Artificial lake induced earthquakes Earthquakes initiated by people (e.g. blasting) 11

12 Global Tectonic Activity Map 12

13 Global Seismicity Earthquakes with Magnitude > 3 13

Terminology Magnitude M Magnitude M measures the energy released at the source of the earthquake.

Intensity measures the strength of shaking produced by the earthquake at a certain location.

14 Terminology Magnitude M Magnitude M measures the energy released at the source of the earthquake. It is determined from measurements on seismographs. An increase by 1 (e.g. from 7 to 8) corresponds to an increase of the source energy by a factor of ~32 Intensity I Intensity measures the strength of shaking produced by the earthquake at a certain location. It is determined from and refers to effects on people, structures, and the natural environment I + 1 ~ acceleration x 2 For the description of the intensity different scales are used. Valid for Europe is the European Macroseismic Scale EMS-98 14

Earthquake Intensity EMS 98 - European Macroseismic Scale EMS Intensity Definition I Not felt Not felt. II Scarcely Felt Felt only by very few individual people at rest in houses.

15 Earthquake Intensity EMS 98 - European Macroseismic Scale EMS Intensity Definition I Not felt Not felt. II Scarcely Felt Felt only by very few individual people at rest in houses. Description of typical observed effects abstracted (This short form is not suitable for intensity assignments.) III Weak Felt indoors by a few people. People at rest feel a swaying or light trembling. IV Largely Observed Felt indoors by many people, outdoors by very few. A few people are awakened. Windows, doors and dishes rattle. V Strong Felt indoors by most, outdoors by few. Many sleeping people awake. A few are frightened. Buildings tremble throughout. Hanging objects swing considerably. Small objects are shifted. Doors and windows swing open or shut. VI Slightly Damaging Many people are frightened and run outdoors. Some objects fall. Many houses suffer slight non-structural damage like hairline cracks and fall of small pieces of plaster. VII Damaging Most people are frightened and run outdoors. Furniture is shifted and objects fall from shelves in large numbers. Many well built ordinary buildings suffer moderate damage: small cracks in walls, fall of plaster, parts of chimneys fall down; older buildings may show large cracks in walls and failure of fill-in walls. VIII Heavily Damaging Many people find it difficult to stand. Many houses have large cracks in walls. A few well built ordinary buildings show serious failure of walls, while weak older structures may collapse. IX Destructive General panic. Many weak constructions collapse. Even well built ordinary buildings show very heavy damage: serious failure of walls and partial structural failure. X Very Destructive Many ordinary well built buildings collapse. XI Devastating Most ordinary well built buildings collapse, even some with good earthquake resistant design are destroyed. XII Completely devastating Almost all buildings are destroyed. 15

16 Acceleration, g Earthquake Response Magnitude and Intensity cannot yet serve a basis for structural design Information on Amplitude Frequency content Duration is needed Time t, Seconds Ground motion acceleration El Centro earthquake 16

17 Earthquake Response Magnitude and Intensity cannot yet serve a basis for structural design Newton s second law of motion Force = mass x acceleration Information on Amplitude Frequency content Duration is needed F i = m x a Ground motion acceleration 17

18 Spectral Acceleration, g Acceleration, g Spectral Acceleration, g Earthquake Response Spectrum Representation in codes Frequency f, Hz Time t, Seconds Period T, Seconds Ground motion acceleration El Centro earthquake Acceleration response spectrum El Centro earthquake Generalized shape of smoothed design response spectrum 18

19 Spectral Acceleration, g Earthquake Response Spectrum g Period T, Seconds f = 2 Hz T = 0.5 s a 1 g for T = 0.2 s 19

20 Spectral Acceleration, g Earthquake Response Spectrum g Period T, Seconds f = 2 Hz T = 0.5 s a 1 g for T = 0.2 s Imagine a building attached to the wall 20

21 Global Seismic Hazard Map 4 m/s² 21

22 European Seismic Hazard Map [Giardini et al] 22

23 Example Text Headline, second line of headline Body text, second line of body text Earthquake Risk = First bullet layer First bullet layer Headline, second line of headline Body text, second line of body text First bullet layer First bullet layer - Second Hazard bullet layer x Vulnerability - Second bullet layer x Exposure - Second bullet layer - Second bullet layer 23

24 Victim and Damage Statistics of two Earthquakes with comparable Magnitude Spitak (Armenia) 1988 Loma Prieta (US) 1989 C.J. Langer. U.S. Geological Survey H.G. Wilshire, U.S. Geological Survey Human Toll > 25, Injured 31,000 2,435 Unsheltered 514,000 7,362 Property damage unknown > 6 Billion US$ 24

25 Old vs. New 2008 Sichuan Earthquake, China 25

26 not always true 26

27 Vulnerabilities! Vulnerability Human toll Property losses Disruption of function Business Interruption Engineering Task Avoid structural failure Limit damages Maintain function Consider the whole system not just the building Think global not local Business interruption may result from Direct damage to building, equipment or critical contents. Damages to interrelated businesses. Losses of utilities or transportation modes. Loss of availability of supplies. Off site damage of transit systems, power, telecommunications, utilities, water or waste water treatment facilities. 27

28 Scope of Seismic Design Codes UBC, 1997 ed. Section 1626 to safeguard against major structural failures and loss of life, not to limit damage or maintain function EN 1998, Eurocode 8 purpose is to ensure that in the event of earthquakes: Human lives are protected Damage is limited Structures important for civil protection remain operational 28

Performance Based Design Repairable Irreparable EN 1998, Eurocode 8 No-collapse requirement For a ground shaking with a 10 % chance of being exceeded in 50 years

29 Performance Based Design Repairable Irreparable EN 1998, Eurocode 8 No-collapse requirement For a ground shaking with a 10 % chance of being exceeded in 50 years Return period 475 years Damage limitation requirement For a ground shaking with a 50 % chance of being exceeded in 50 years Return period 72 years Vision 2000 Committee 29

30 Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity Redundancy Ductility The decisive step towards seismic design consists in thinking of the transfer of horizontal loads from the purely constructional point of view. All further measures are improvements of thinking by a more exact quantification of the additional loads, more exact calculations of the stresses a colleague of mine 30

Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity

31 Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity Redundancy Ductility Constant or continuously decreasing stiffness over the structural height, as far as possible no steps or offsets, no soft storey 31

32 Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity Redundancy Ductility Stiffness and mass centers should be as close as possible to each other 32

33 Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity Redundancy Ductility Stiffness and mass centers should be as close as possible to each other 33

strength Regularity Redundancy Ductility 2010 Canterbury

34 H Important Seismic Design and Construction Features Stable foundations Continuous load paths Adequate stiffness and strength Regularity Redundancy Ductility 2010 Canterbury Earthquake, New Zealand 11% H 2011 Tōhoku-Erdbeben, Japan Foto: Lignos 35

Prediction of Seismic Behavior SMART 2013

table tests with analysis results for design and

3 storey reinforced concrete building Braced by shear

35 Prediction of Seismic Behavior SMART 2013 international benchmark Scope: Comparison of shaking table tests with analysis results for design and beyond design earthquakes. 3 storey reinforced concrete building Braced by shear wall, unsymmetrical in plain Designed against seismic loads of 0.2 g 1/4th reduce scaled model 36

36 Horizontal displacement, m Wölfel 2015 Prediction of Seismic Behavior SMART 2013 international benchmark Design: PGA 0.2 g Beyond design: PGA ~ 1.0 g Shaking Table Test Simulation Wölfel Time t, Seconds 37

Structural Vulnerability Assessment of Existing

Level 1 Level 2 Level 3 Level >3 Desktop, screening

testing of readily available areas) Site visit +

review (numerical simulation, material testing)

37 Structural Vulnerability Assessment of Existing Buildings Typical Levels of Investigation Level 0 Level 1 Level 2 Level 3 Level >3 Desktop, screening Site visit (visual inspection, non-destructive testing of readily available areas) Site visit + review of design documents Detailed engineering review (numerical simulation, material testing) Seismic Probabilistic Safety Analysis, Probabilistic Seismic Margin Assessment 38

walls Appropriate seismic gaps Anchorage of non-structural components Presence of cracks or other structural

38 Site Visit / Seismic Walkdown Points to consider Regularity of stiffness and mass distribution in plan and elevation Suitability of construction material and type of construction Arrangement of bracings / stiffening walls Appropriate seismic gaps Anchorage of non-structural components Presence of cracks or other structural damages Highly experienced engineers are necessary Preparation is the key for a successful seismic walkdown 39

39 Retrofit of Buildings Courtesy of Wenk Wikipedia.org Courtesy of Lignos Wikipedia.org Reinforcement with bracings Jacketed and grouted column on left, unmodified on right 40

40 Retrofit of Buildings Courtesy of Wenk Strenghtening out of plane Reinforcement of masonry with CFRP Courtesy of Wenk Courtesy of Wenk Eccentric braces with dampers Seismic base isolation 41

41 Conclusions Earthquakes are infrequent, but inevitable in seismic areas. The main focus of structural engineers was and still is to save life, not to limit damage. Future trend is to develop damage resistant structures that minimize economic loss and allow rapid post-event recovery. The prediction of a realistic seismic behavior by structural analysis is getting better and better. Site visits / seismic walkdowns are essential for the assessment of existing structures. But they have to be carefully planned and executed. 42

42 Thank you for your Attention! Woelfel Beratende Ingenieure GmbH + Co. KG Max-Planck-Str Hoechberg Germany Dr.-Ing. Carsten Block Tel.: block@woelfel.de Tel.: Fax: wbi@woelfel.de 43

43 References Prof. Stephan Mahin, Understanding and Coping with Risks of Living in Earthquake Country, Lecture presentation in Statistics/Computer Science/Political Science C79 Societal Risks and the Law Roberto Villaverde, Fundamental Concepts of Earthquake Engineering, CRC Press, 2009 FEMA P-749, Earthquake-Resistant Design Concepts, December

Earthquakes 101. Instructor: Stanton Smith, P.E.

Earthquakes 101. Instructor: Stanton Smith, P.E. Earthquakes 101 Instructor: Stanton Smith, P.E. Presentation Outline Earthquake Terminology Earthquake Damage Potential Magnitude Source to Site Distance Soil Conditions Type of Construction Residential