The Grand Chancellor was a 22-story reinforced concrete tower. The top 15 stories functioned as hotel accommodations. The lobby of the hotel was located on the ground floor. The top six stories above the ground floor were car parking floors separated into...

Prepared By: Edwin Lim
Occupancy: Hotel
Year Built: 1988
Height: 85 m
Number of stories: 22
Stories below ground: 0
Size: 792 sqm
Original Code: NZS4203:1984 (structural design and design loading code), NZS3101:1982 (concrete code)
Modification: none
Year Modified: N/A
Code of Modification: N/A
Lateral Load System: Moment Frame and Shear Wall Combination
Other Load System:
Vertical Load System: Other
Other Vertical Load System: In-situ flat slab (ground to level 14), precast-prestressed rib and timber infill with in-situ topping and frames (level 14 - 28
Foundation : Piles or Piers
Other Foundation :
Country: New Zealand
State:
City: Christchurch
Street: 161 Chasel Street
Latitude: -43.532891
Longitude: 172.638826


 

Grand Chancellor

Earthquake Information

 

 

Earthquake Date 40596
Moment Magnitude 6.1
Epicentral Distance 6.485
Local Intensity VIII MMI
Site Description Site Class D (Kam,et al 2011)
PGA Lateral 0.531 (g)
PGA Vertical 0.5 (g)
SaT
Ground motion recording stations Christchurch Cathedral College, Christchurch Botanic Gardens, Christchurch Hospital, Christchurch Resthaven
Distance to station None
Station Latitude None
Station Longitude None
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

In the September 2010 main shock there was no significant damage to this building. However, it was subjected to significant structural damage during the February 2011 aftershocks. The Grand Chancellor appeared to have been generally well designed except for the critical shear wall D5-6. Some redundancy and resilience within other areas of the structure prevented total collapse. As a result of the shear wall failure, the southeast corner of the building dropped by approximately 800 mm and displaced approximately 1300 mm at the top of the building. (Dunning Thornton Consultant, 2011)

Damage state description

The damage in this building was caused by the failure of shear wall D5-6. This shear wall was subjected to critical shear failure which resulted in a shortening of about 800 mm. The wall slid diagonally toward the west end of the building. The movement induced by the collapse of this wall caused failure in columns (B5, B6, C5, C6), beam yielding, stair collapse and precast panel dislodgement. In addition, there was some damage to the slab and indication of pounding on the west side of the building. Structural damage in other parts of the building was consistent with what may be expected from a well-designed reinforced concrete structure in a seismic event of this intensity. (Expert Panel Report, 2011 & Dunning Thornton Consultant, 2011)

Summary of causes of damage

Factors contributing to failure of critical shear wall: 1. Larger than expected ground motion, 2. Larger than expected acceleration and displacement demand to the building, 3. Higher axial loads than allowed for in the design, 4. The coincidence of high vertical accelerations with strong horizontal actions, 5. The lack of robustness and resiliency of the wall and its inability to sustain loads in excess of those allowed for in the design. Factors contributing to a critical vulnerability within the building: 1. Horizontal irregularity from the cantilevering transfer girder resulting in a disproportionate contributing area supported by the damage shear wall 2. Vertical irregularity from a framed structure on top of shear wall podium with transfer beam at the interface 3. Extremely high axial load at wall due to gravity loads; axial load resulting from over-strength beam shear; action resulting from in-plane forces in the story-high cantilever transfer beams; vertical earthquake actions; code defined actions exceeded by the February 2011 aftershock 4. Wall slenderness ratio that did not meet code requirements for the levels of axial load 5. Insufficient confinement at the base of the damage wall, with respect to code 6. Insufficient available ductility in the critical wall relative to the demands of the February 2011 aftershocks 7. Lapping in a wall end/hinge zone Stair flights collapse: 1. Displacement of building due to failure of the damage wall (Expert Panel Report, 2011)

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete Based on concrete strength of core samples that correspond with the specified strength of the shear wall
Reinforcing steel Deformed rebar was used for the longitudinal reinforcement. Meanwhile, unaltered rebar might be found in transverse reinforcement.

ExecutionNotesContribution to Damage
Conveyance/placement of concrete
Rebar Wall D5-6 was lightly reinforced with only nominal confinement reinforcing.
Field variance with design documents
OtherNotesContribution to Damage
Other Factors Construction Quality Structural redesign: due to permit issue (refer to top left figure in page 3)

Configuration

Plan IrregularitiesNotesContribution to Damage
Torsion
Perimeter boundary Podium and entrance in the south side and suspended vehicle ramps in the north side
Diaphragm
Out-of-plane offsets in lateral resisting system East side cantilever in the structure
Non-orthogonal systems

Vertical IrregularitiesNotesContribution to Damage
Soft story There was damage to columns and shear walls, but this was only found in some locations, not entire floor
Weak story There was damage to columns and shear walls, but this was only found in some locations, not entire floor
Geometric variablility of lateral resisting system Cantilever transfer beam appeared above Tattersalls lane
In-plane discontinuity of lateral resisting system Shear wall was only provided in the bottom portion of tower; perimeter frame on the cantilever was only found in the upper portion of tower
Mass distribution Cantilever section of upper tower may cause changing of center of mass between upper and bottom tower
Setback Setback of podium and atrium on the north and south side of tower
Change in stiffness Upper portion was framing system and bottom portion was framing system with shear wall

OtherNotesContribution to Damage
Other Factors Configuration

Lateral Load Resisting System‐General

StrengthNotesContribution to Damage
Overall lack of strength Overall, the design had satisfied the code at that time except for shear wall D5-6

StiffnessNotesContribution to Damage
Extreme Flexibility

Load PathNotesContribution to Damage
Collectors/Struts Transfer beam 8D-E
Anchorage of nonstructural elements Precast panel connection
Out-of-plane capacity of walls Wall D5-6 had potential to attract out-of-plane moment and shear load corresponding to its stiffness
Diaphragm chords
Diaphragm openings

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-General

Lateral Load Resisting System‐Frames

ColumnsNotesContribution to Damage
Shear strength There was damage in columns (B5, B6, C5, C6), but it was caused by the combination of axial and moment forces.
Flexural strength
Axial load ratio
Vertical load columns drift capacity
Interference of frame action by infill No reported captive column effect.

BeamsNotesContribution to Damage
Strength relative to columns Beam yielding was observed in some locations (lower and upper tower)
Shear controlled behavior
Continuity of longitudinal reinforcing Near lap-splice failure in transfer beam
Loss of vertical capacity The transfer beam has come close to collapse
Interference of frame action by infill beams

JointsNotesContribution to Damage
Interior
Exterior
Corner

OtherNotesContribution to Damage
Other Factors Lateral Load Resisting System-Frames Combination of axial and moment forces imposed by lateral displacements. These were caused by the rotation of the transfer beam for columns B5, B6, C5, and C6.

Lateral Load Resisting System‐Shear Walls

ShearNotesContribution to Damage
Diagonal tension/compression Occurred in D5-6 shear wall
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 Hairline flexural crack in the ground floor shearwalls (not D5-6)

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 With the adjacent parking structure on the west side of the building
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

Stabilization

Other Retrofit or Repair

Performance Level

NA

Hazard Level

NA

Retrofit or Repair Code

NA

Other Retrofit or Repair Code

Lateral Analysis

NA

Other Lateral Analysis

Design Strategy

Retrofit Summary

Concrete encasement for temporary stabilization.

References

 

http://db.concretecoalition.org/static/data/6-references//NZ001_Reference_2.pdf
Dunning Thornton Consultants, 2011.Report on the Structural Performance of the Hotel Grand Chancellor in the Earthquake of 22 February 2011, New Zealand.


http://db.concretecoalition.org/static/data/6-references/NZ001_Reference_1.pdf
New Zealand Department of Building and Housing Expert Panel, 2011,Structural Performance of Christchurch CBD Buildings in the 22 February 2011 Aftershocks: Stage 1 Expert Panel Report, New Zealand., Redwood City, CA.


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.


United States Geological Survey (USGS), 2011.Magnitude 6.1 - SOUTH ISLAND OF NEW ZEALAND, (Accessed: 12 July 2012)


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


http://www.geonet.org.nz/earthquake/historic-earthquakes/top-nz/quake-14.html
GeoNet, 2011.M 6.3, Christchurch, February 22 2011. (Accessed: 12 July 2012).


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