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Performance of buildings in the February 2011 Christchurch Earthquake

Sixth International Conference on Seismology and Earthquake Engineering 16-18 May 2011, Tehran, Iran. Performance of buildings in the February 2011 Christchurch Earthquake. Associate Prof Rajesh Dhakal University of Canterbury Christchurch, NZ. URM Buildings: General Observations.

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Performance of buildings in the February 2011 Christchurch Earthquake

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  1. Sixth International Conference on Seismology and Earthquake Engineering 16-18 May 2011, Tehran, Iran Performance of buildings in the February 2011 Christchurch Earthquake Associate Prof Rajesh Dhakal University of Canterbury Christchurch, NZ

  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

  3. Many buildings were about to collapse (short duration effect)

  4. In-plane wall/pier failure

  5. Gable wall failure

  6. Parapet Failures

  7. Anchorage Failure

  8. Out-of-plane wall failure

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

  10. Poor quality of mortar Τ = C + µ N Many tested samples 1.0-1.5 MPa compression strength

  11. Poor quality of diaphragm timber

  12. Inadequate Cavity Wall Ties

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

  14. Pounding Survey statistics ≥ ≥ ≥ ≥ ≥

  15. Typical masonry pounding damage

  16. URM pounding damage mechanism

  17. Diagonal damage path due to pounding

  18. Buildings in a row with little separation

  19. Example: Pounding damage

  20. Example: Pounding damage

  21. Example: Pounding damage

  22. Example: Pounding damage

  23. Inadequate building flashing details

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

  25. Some well-anchored walls did well

  26. Damage to anchored walls

  27. Steel strong backs generally performed well

  28. Steel Frames: Generally did well

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

  30. Wall confined by steel plates • (cracks visible, but not wide)

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

  32. Floor Diaphragms Retrofit

  33. Successful parapet strengthening

  34. Unsuccessful Parapet Strengthening (require protection at corners)

  35. Unsuccessful Parapet Strengthening Wall detached from struts

  36. 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

  37. CTV Building (117 dead)

  38. Hotel Grand Chancellor (Demolished)

  39. 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

  40. Example: Clarendon Tower

  41. Dislodging of precast stair from landing

  42. Dislodging of precast stair from landing

  43. Vertical acceleration effect

  44. 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

  45. Non-structural damage

  46. 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

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