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

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)

In-plane wall/pier failure

Gable wall failure

Parapet Failures

Anchorage Failure

Out-of-plane wall failure

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

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

Poor quality of diaphragm timber

Inadequate Cavity Wall Ties

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

Pounding Survey statistics

Typical masonry pounding damage

URM pounding damage mechanism

Diagonal damage path due to pounding

Buildings in a row with little separation

Example: Pounding damage

Inadequate building flashing details

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

Some well-anchored walls did well

Damage to anchored walls

Steel strong backs generally performed well

Steel Frames: Generally did well

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.

Floor Diaphragms Retrofit

Successful parapet strengthening

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

CTV Building (117 dead)

Hotel Grand Chancellor (Demolished)

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

Example: Clarendon Tower

Dislodging of precast stair from landing

Vertical acceleration effect

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 damage

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