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Performance of buildings in the February 2011 Christchurch Earthquake Associate Prof Rajesh Dhakal University of Canterbury Christchurch, NZ Sixth International.

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Presentation on theme: "Performance of buildings in the February 2011 Christchurch Earthquake Associate Prof Rajesh Dhakal University of Canterbury Christchurch, NZ Sixth International."— Presentation transcript:

1 Performance of buildings in the February 2011 Christchurch Earthquake Associate Prof Rajesh Dhakal University of Canterbury Christchurch, NZ Sixth International Conference on Seismology and Earthquake Engineering May 2011, Tehran, Iran

2 URM Buildings: General Observations Extensive damage to URM buildings in general Many URM buildings in the city flattened Most of the remaining buildings very severely damaged Few well constructed URM buildings in the western suburbs were subjected to moderate shakings and suffered repairable damage In the CBD, very few (unretrofitted) URM buildings will exist in future. Some examples of typical URM building damage/collapse follow

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6 Many buildings were about to collapse (short duration effect)

7 In-plane wall/pier failure

8 Gable wall failure

9 Parapet Failures

10 Anchorage Failure

11 Out-of-plane wall failure

12 Vulnerability of cavity construction Out-of-plane failures (Cavity walls)

13 Poor quality of mortar Many tested samples MPa compression strength Τ = C + µ N

14 Poor quality of diaphragm timber

15 Inadequate Cavity Wall Ties

16 Pounding of URM Buildings Acknowledgement: Several slides in this section are provided by Gregory Cole, University of Canterbury

17 Pounding Survey statistics

18 Typical masonry pounding damage

19 URM pounding damage mechanism

20 Diagonal damage path due to pounding

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22 Buildings in a row with little separation

23 Example: Pounding damage

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27 Inadequate building flashing details

28 Performance of Retrofitted URM Buildings Acknowledgement: Several slides in this section are provided by A/P Jason Ingham, University of Auckland

29 Some well-anchored walls did well

30 Damage to anchored walls

31 Steel strong backs generally performed well

32 Steel Frames: Generally did well

33 Steel Frames: Some suffered damage Failed frame to wall connections mounted perpendicular to wall

34 Wall confined by steel plates (cracks visible, but not wide)

35 Shotcrete In general shotcreted masonry walls performed well. Minor cracking seen in some walls.

36 Floor Diaphragms Retrofit

37 Successful parapet strengthening

38 Unsuccessful Parapet Strengthening (require protection at corners)

39 Unsuccessful Parapet Strengthening Wall detached from struts

40 Performance of Old RC buildings Designed for smaller strength (compared to now) Subjected to large acceleration (higher than current design level) Lacked ductility (specially the pre-1980 buildings) Mostly not retrofitted As expected, damaged severely

41 CTV Building (117 dead)

42 Hotel Grand Chancellor (Demolished)

43 Performance of Modern RC buildings Subjected to large acceleration (higher than current design level) Inherent ductility As expected, most buildings damaged But no collapse (post 1990) Most buildings can be reused after repair (bonus?) In general, performance better than expected

44 Example: Clarendon Tower

45 Dislodging of precast stair from landing

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47 Vertical acceleration effect

48 Issues related to performance of modern buildings Staircase in many buildings collapsed (change of current practice needed) Precast floor (issues with interaction between floor and beam elongation) Irregularity of buildings (irregular buildings performed poorly) Foundation: Not adequate for the soft soil underneath Compression failure of columns: high vertical acceleration

49 Non-structural damage

50 Non-structural performance Structural performance: no surprises Non-structural performance: DISAPPOINTING Ceiling: Very few buildings with ceilings intact Facade/Partition: Damaged severely in most buildings Parapets: Most unrestrained parapets fell September earthquake: Minor structural damage (modern buildings); severe non-structural damage February earthquake: Moderate-severe damage to modern buildings; Collapse of non-structural elements Clearly, a mismatch between the structural and non- structural performance Need more focus in future

51 Non-structural damage could have killed more people

52 Falling objects could have, too It is time that we start explicitly aiming for minimisation of NON-STRUCTURAL DAMAGE and DOWNTIME in seismic design.

53 Relevance to Iran 1.There are many unreinforced masonry (URM) buildings which can suffer severe damage in moderate shakings and collapse in strong shakings. The brittle failure of URM building components can be fatal. 2.Systematically strengthened/retrofitted URM buildings perform noticeably better. Although they may suffer damage in large earthquakes, they are unlikely to collapse completely; thereby saving lives of inhabitants. 3.Hence, if you want to reduce the life safety threat from these URM buildings, you MUST retrofit them. 4.Be careful, there is a difference between strengthening and retrofitting.

54 Thank You! Acknowledgements: Jason Ingham, and Gregory Cole for providing some photographs and slides


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