Ductility is Damage People Don t want to live in Damaged Buildings Akira Wada Professor Emeritus Tokyo Institute of Technology

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1 ATC & JSCA Ductility is Damage People Don t want to live in Damaged Buildings Akira Wada Professor Emeritus Tokyo Institute of Technology

2 Professors recommend Ductile Frames to students. Akira Wada ATC & JSCA 2

3 Ductility is Damage 1/2 The Ds values are 0.25 to 0.55 in Japanese seismic design procedure, and the R factors are 2 to 8 in the USA. Almost all structural engineers rely on the plastic deformability of beams, columns and walls of building structures during seismic design of structures. Akira Wada ATC & JSCA 3

4 Ductility is Damage 2/2 The ductility as plastic deformation of frames is the damage of structures. This is easy to understand for young boys and girls to old ladies and gentlemen. Normal people don t want to live in the damaged buildings. Then, these damaged buildings become to be demolished after the big earthquake. Akira Wada ATC & JSCA 4

5 Designed to protect life in extreme event, but damage is expected Prof. Stephen Mahin said. Akira Wada ATC & JSCA 5

6 Kobe Earthquake 1995 Akira Wada ATC & JSCA 6 株式会社新井組 1995 年技術研究報告集より

7 Akira Wada ATC & JSCA 株式会社新井組 1995 年技術研究報告集より 7

8 Perfectly Demolished after 1995 Earthquake Akira Wada ATC & JSCA 株式会社新井組 1995 年技術研究報告集より 8

9 All trucks were bringing huge gavages produced from collapsed buildings and demolished buildings.

10 Residual displacements of 14 story Steel Concrete Apartment Building in Sendai-City Akira Wada ATC & JSCA 10

11 Residual displacements of 14 story Steel Concrete Apartment Building in Sendai-City Akira Wada ATC & JSCA 11

12 12 story Steel Concrete Apartment Building of Sendai-City Akira Wada ATC & JSCA 12 Courtesy of Prof. Yasushi Sanada, Osaka University

13 Christchurch before 2011 Earthquake Akira Wada ATC & JSCA 13

14 Christchurch after 2011 Earthquake

15 Current Seismic Design H. Only Human life to be safe B. Building cannot use after repair C. No Continuous Use after earthquake We can not make our city sustainable and resilience against big earthquake. We need to change our seismic design concept. Akira Wada ATC & JSCA 15

16 New Seismic Design H. Human life have to be safe B. Building can use after some repaired C. Continuous Use just after earthquake Against Small and Medium Earthquake ---- We can satisfy H, B and C easily. Against Big Earthquake We have to satisfy H and B, some case C. Akira Wada ATC & JSCA 16

17 New Seismic Structures Seismic Isolated Structures Passive Controlled Structures Stepping Columns Structures Elastic Joints of Pre-casted RC Other Good Structures Akira Wada ATC & JSCA 17

18 Seismic Isolated Steel Tall Building constructed in TITech. Akira Wada ATC & JSCA 18

19 Seismic isolated apartment buildings taller than 30 story buildings Akira Wada ATC & JSCA 19

20 Damage Controlled Structures = + Building Structures Primary Structure Seismic Members (To Support Vertical Load) (To absorb earthquake energy) Akira Wada ATC & JSCA 20

21 We have to learn good ideas from Nature Some kind of Sacrifice for Human Body Collar bone Akira Wada ATC & JSCA 21

22 A Bumper protecting people and Bus Akira Wada ATC & JSCA 22

23 A Fuse protecting important PC Akira Wada ATC & JSCA 23

24 Akira Wada ATC & JSCA 24

25 Detail of Unbonded Braces 4.0m 6.4m Akira Wada ATC & JSCA 25

26 Many Unbonded Braces are Installed Akira Wada ATC & JSCA 26

27 Fig. 1 Earthquake ground motion vs. Damage or Repair cost Akira Wada ATC & JSCA 27

28 Akira Wada ATC & JSCA 28

29 Now in Tokyo Akira Wada ATC & JSCA 29

30 ----Seismic intensity Damages of buildings in the city after big earthquake, in the case that all buildings were designed as ductile frame structure. Akira Wada ATC & JSCA 30

31 ----Seismic intensity Damages of buildings in the city after big earthquake, in the case that all buildings were designed as strength oriented structure. Akira Wada ATC & JSCA 31

32 ----Seismic intensity Damages of buildings in the city after big earthquake, in the case that all buildings were designed as passive controlled structures. Akira Wada ATC & JSCA 32

33 ----Seismic intensity Almost no damage of building in the city after big earthquake, in the case that all buildings were designed as seismic isolated structures. Akira Wada ATC & JSCA 33

34 Big earthquake occurs Many buildings in the city Present Year Almost all buildings will be perfectly collapsed by the next big earthquake when these buildings have poor seismic performance. Akira Wada ATC & JSCA 34

35 Big earthquake occurs Many buildings in the city Present Year Many buildings will be demolished after the next big earthquake when these buildings are designed by ductile moment structural system. Akira Wada ATC & JSCA 35

36 Big earthquake occurs Many buildings in the city Present Year Only few buildings will suffer damages by the next big earthquake when all buildings are using seismic isolated or passive controlled structures or new technologies. Akira Wada ATC & JSCA 36

37 Conclusion 1/3 Who does pay money for demolishing many damaged buildings and clean up the damaged city? Does money come from insurance, city, prefecture, government or owner? When owner did not need to pay it, they will built ductile building, because it seems like cheap. A city is consisted of many buildings. Akira Wada ATC & JSCA 37

38 Conclusion 2/3 After major earthquake, structural engineers put red tags to damaged buildings, even if these buildings are not so severe damage, they tend to put red tag. People don't want to return to the red tag building. When many buildings were demolished in a city, we can not stay in the city and we can t say that we make a resilient city. Akira Wada ATC & JSCA 38

39 Conclusion 3/3 We have to consider not only resilience of a building, but also resilience of a city consist of many buildings. Then we can not recommended to make buildings rely to large ductility. When we make a rule that owner have to pay, people will built his building more strong. Akira Wada ATC & JSCA 39

40 An individual building is component of a big city The probability of occurrence of a large earthquake ground motion could be neglected in the design process of a building under the economic consideration and the engineering judgments. However, this would be a big gamble of the city. Akira Wada ATC & JSCA 40

41 Seismic design for a big city The seismic issues of a city cannot be solved, if the seismic resistance of its individual building is determined only from the relationship between the life of a single building and the earthquake occurrence in its life span. We have to make resilience city and country against big earthquake. Akira Wada ATC & JSCA 41

42 Prof. Robert Park at Canterbury University Prof. R. Park introduced ductile moment reinforced concrete frames in earthquake prone countries, but he have said at that time: Ductility is not final goal. Akira Wada ATC & JSCA 42

43 Thank you very much for your attention. We, structural engineers, have a mission to make the world a better place to live. Akira Wada Akira Wada ATC & JSCA 43