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:
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 16-18 May 2011, Tehran, Iran
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
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
Non-structural damage could have killed more people
Falling objects could have, too It is time that we start explicitly aiming for minimisation of NON-STRUCTURAL DAMAGE and DOWNTIME in seismic design.
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.
Thank You! Acknowledgements: Jason Ingham, and Gregory Cole for providing some photographs and slides