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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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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 • 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
Many buildings were about to collapse (short duration effect)
Out-of-plane failures (Cavity walls) Vulnerability of cavity construction
Poor quality of mortar Τ = C + µ N Many tested samples 1.0-1.5 MPa compression strength
Pounding of URM Buildings Acknowledgement: Several slides in this section are provided by Gregory Cole, University of Canterbury
Pounding Survey statistics ≥ ≥ ≥ ≥ ≥
Performance of Retrofitted URM Buildings Acknowledgement: Several slides in this section are provided by A/P Jason Ingham, University of Auckland
Steel Frames: Some suffered damage Failed frame to wall connections mounted perpendicular to wall
Wall confined by steel plates • (cracks visible, but not wide)
Shotcrete In general shotcreted masonry walls performed well. Minor cracking seen in some walls.
Unsuccessful Parapet Strengthening (require protection at corners)
Unsuccessful Parapet Strengthening Wall detached from struts
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
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
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
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