This 11-story frame and shear wall building in the Central Business District of Christchurch had two sets of 200 mm thick L-shaped shear walls on the north and south faces of the building that terminated just above the basement and relied on a transfer b...

Prepared By: Quinn Peck
Occupancy: Hotel
Year Built: 1985
Height: ft
Number of stories: 11
Stories below ground: 0
Size: gsf
Original Code:
Modification: Retrofit
Year Modified: 2010
Code of Modification:
Lateral Load System: Moment Frame and Shear Wall Combination
Other Load System:
Vertical Load System: Slabl_Beams_Columns
Other Vertical Load System:
Foundation : Unknown
Other Foundation :
Country: New Zealand
State: Christchurch Central
City: Christchurch
Street: 335 Durham Street, Christchurch Central, Christchurch 8013, NZ
Latitude: -43.527
Longitude: 172.634


 

11-Story Building

Earthquake Information

 

 

Earthquake Date 2/22/2012
Moment Magnitude 6.1
Epicentral Distance 7.3
Local Intensity VIII MMI
Site Description The vast majority of the Central Business District of Christchurch was constructed on deep alluvial deposits. The February earthquake caused an unprecedented amount of liquefaction in this region due to the interaction of the loose alluvial deposits and the extremely shallow water table (1 meter below the surface in many regions).
PGA Lateral None (g)
PGA Vertical None (g)
SaT
Ground motion recording stations GNS Station REHS (Christchurch Resthaven)
Distance to station 0.4
Station Latitude -43.523
Station Longitude 172.652
Ground Motion Summary The February, 2011 South Island, New Zealand earthquake occurred as part of the aftershock sequence of the M 7.0 September, 2010 Darfield, NZ earthquake. The February earthquake involved oblique-thrust faulting at the easternmost limit of previous aftershocks and, like the main shock itself, is broadly associated with regional plate boundary deformation as the Pacific and Australia plates interact in the central South island, New Zealand. This latest shock was significantly closer to the main population center of Christchurch, NZ than the September main shock, in the vicinity of several other moderate sized aftershocks located east of the main rupture zone of the 2010 event. There is no specific structure directly linking this event to the main fault of the 2010 main shock, although there have been numerous aftershocks along generally east-west linear trends extending east from the end of the previous rupture. The north or north-east trends to the possible fault planes and the oblique thrust faulting mechanism as seen in the focal mechanism solution may reflect an association with similarly-trending faults previously mapped in the Port Hills region, just the south of Christchurch. The February aftershock had an extremely short duration of 8 seconds of strong motion shaking. (USGS)

 

Damage Information

 

 

Performance summary

The Copthorne Hotel experieced severe damage during the Christchurch earthquake and was subsequently demolished.

Damage state description

The discontinuous shear walls in the longitudinal direction of the structure resulted in severe damage in the basement columns as well as the transfer beams and ground floor diaphragm. The presence of the two concrete cores in the south side of the building likely resulted in significant torsional amplication and significantly higher demand on the north face of the building. Nearly all of the basement columns on the northern side suffered shear-axial failures. The excessively strong RFP wrapped beams created a strong-beam weak-column mechanism, resulting in catastrophic failure of basement columns. The transfer girder just above the lobby on the main floor was also significantly damaged.

Summary of causes of damage

1. The discontinuous L-shaped shear walls resulted in significant demands on the transfer beams and slab in the ground floor level and the basement columns, causing extensive spalling and failure of the beams, separation of the slab and severe shear-axial failure in the columns. 2. The torsional amplification caused by the stiffness irregularity from the southern concrete cores resulted in significantly larger forces in the northern portion of the building. The basement columns in this region suffered greatly, with extensive shear-axial failures and some or total loss of of vertical load-carrying capability. 3.The extensive failure and shortening of the columns in the basement resulted in a lateral lean of approximately 200 mm to 400 mm at the roof level. 4. The polymer fiber wrapped transfer beams just below the discontinuous shear walls likely created a strong beam-weak column failure mode in the columns below the discontinuous walls. 5. The large vertical accelerations during the earthquake resulted in a significant overload on the first-floor transfer girder supporting the gravity load from 10 floors of columns. Both ends of this transfer girder exhibited severe spalling of confining concrete in the beam-column joint and the appearance of incipient shear failure.

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete
Reinforcing steel

ExecutionNotesContribution to Damage
Conveyance/placement of concrete
Rebar
Field variance with design documents
OtherNotesContribution to Damage
Other Factors Construction Quality

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion
Perimeter boundary
Diaphragm
Out-of-plane offsets in lateral resisting system
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story
Weak story
Geometric variablility of lateral resisting system
In-plane discontinuity of lateral resisting system
Mass distribution
Setback
Change in stiffness

OtherNotesContribution to Damage
Other Factors Configuration

Lateral Load Resisting System‐General

StrengthNotesContribution to Damage
Overall lack of strength

StiffnessNotesContribution to Damage
Extreme Flexibility

Load PathNotesContribution to Damage
Collectors/Struts
Anchorage of nonstructural elements
Out-of-plane capacity of walls
Diaphragm chords
Diaphragm openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-General

Lateral Load Resisting System‐Frames

ColumnsNotesContribution to Damage
Shear strength
Flexural strength
Axial load ratio
Vertical load columns drift capacity
Interference of frame action by infill

BeamsNotesContribution to Damage
Strength relative to columns
Shear controlled behavior
Continuity of longitudinal reinforcing
Loss of vertical capacity
Interference of frame action by infill beams

JointsNotesContribution to Damage
Interior
Exterior
Corner

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Frames

Lateral Load Resisting System‐Shear Walls

ShearNotesContribution to Damage
Diagonal tension/compression
Sliding Shear
Flexure/shear

FlexureNotesContribution to Damage
Compression zone buckling capacity
Discontinuity of wall
Boundary reinforcing fracture/buckling
Boundary Reinforcing at openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Shear Walls

Lateral Load Resisting System‐Infills

InfillsNotesContribution to Damage
Unreinforced
Interference with frame action
Out of plane
Attachment to framing

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting Systems-Infills

Lateral Load Resisting System‐Other

FoundationsNotesContribution to Damage
Liquefaction
Pounding
Surface Rupture

OtherNotesContribution to Damage
Pile/Pier tension capacity

MiscellaneousNotesContribution to Damage
Spread footing capacity
Other Factors Lateral Load Resisting Systems-Other-Foundations

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting Systems-Other-Misc

Repair and Retrofit Information

 

Type of Retrofit or Repair

None (demolished/abandoned)

Other Retrofit or Repair

Performance Level

Unknown

Hazard Level

Unknown

Retrofit or Repair Code

Unknown

Other Retrofit or Repair Code

Lateral Analysis

Unknown

Other Lateral Analysis

Design Strategy

While the structure was torn down following the February 22 event, it is important to note that the building had undergone a minor retrofit after the main shock in September. The transfer girders in the first floor supporting the discontinuous shear walls had been wrapped with a fiber reinforced polymer after being damaged in the September event.

Retrofit Summary

References

 

GeoNet, 2011. Canterbury Quakes.http://www.geonet.org.nz (10 July 2012).


GNS Science, 2011. Canterbury Quakes.http://www.gns.cri.nz/ (10 July 2012)


http://db.concretecoalition.org/static/data/6-references/NZ002_Reference_3.pdf
Kam, W.Y., Pampanin, S., and Elwood, K., 2011. Seismic Performance of Reinforced Concrete Buildings in the 22 February Christchurch (Lyttelton) Earthquake,Bulletin of the New Zealand Society for Earthquake Engineering,44, 239178.


Center for Earthquake Strong Motion Data (CESMD), 2011.New Zealand Earthquake of 21 February 2011,http://strongmotioncenter.org (10 July 2012).


United States Geological Survey (USGS), 2011.CISN ShakeMap: South Island of New Zealand,http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/b0001igm/ (10 July 2012).


http://db.concretecoalition.org/static/data/6-references/NZ002_Reference_6.pdf
Earthquake Engineering Research Institute (EERI), 2011. The M 6.3 Christchurch, New Zealand, Earthquake of February 22, 2011.Learning from Earthquakes, EERI Special Earthquake Report.


http://db.concretecoalition.org/static/data/6-references/NZ002_Reference_7.pdf
Cubrinovksi, M. and I. McCahon, 2011. Foundations on Deep Alluvial Soils, University of Canterbury, Christchurch.


http://db.concretecoalition.org/static/data/6-references/NZ002_Reference_8.pdf
Cubrinovski, M., et al., 2011. Geotechnical Aspects of the 22 February 2011 Christchurch Earthquake, Bulletin of the New Zealand Society for Earthquake Engineering. 12 July 2012.


Elwood, K., 2011. Select photos from 21 February 2011 Christchurch, New Zealand Earthquake. Earthquake Engineering Research Institute Photo Library, Oakland, CA.