This building consisted of two v-shaped shear walls on the north and south sides of the building. The south side wall was surrounded by stairs and an elevator. Meanwhile, the north side wall had a direct connection to the diaphragm. This building also had...

Prepared By: Edwin Lim
Occupancy: Commercial
Year Built: 1985
Height: 23.1 m
Number of stories: 7
Stories below ground: 0
Size: 1197 sqm
Original Code: NZS4203:1984 (assumed from the stamped date of building drawings by City Council)
Modification: Unknown
Year Modified:
Code of Modification:
Lateral Load System: Shear Wallrete
Other Load System: Note: the frames appear to be generally proportioned to resist gravity loads and likely contribute nominally to resistance of la
Vertical Load System: One-way slab and beams with columns
Other Vertical Load System:
Foundation : Piles or Piers
Other Foundation :
Country: New Zealand
State: Canterbury
City: Christchurch
Street: 123 Victoria Street
Latitude: -43.52395
Longitude: 172.629968


 

7-Story V-shape Shear Wall Building

Earthquake Information

 

 

Earthquake Date 40596
Moment Magnitude 6.1
Epicentral Distance 7.708
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 (CCCC), Christchurch Botanic Gardens (CBGS), Christchurch Hospital (CHHC), Christchurch Resthaven (REHS)
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 is significantly closer to the main population center of Christchurch, NZ that is 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 south of Christchurch (USGS, 2012).

 

Damage Information

 

 

Performance summary

After the February event, the building was red tagged and a few months after the earthquake, this building was demolished. The main damage occurred to the north V-shaped shearwall. Despite this severely damage shear wall, all occupants were able to safely egress the building after surviving an essentially MCE-level seismic event. This could be described as achieving the Building Code's intent of "Life Safety" or at-least "Collapse Prevention."

Damage state description

The wall buckled over a height of approximately 1 m and crushing extended over 3 meters into the web. Horizontal cracks were visible at the buckled end of the web, while inclined cracks (at approximately 45 degrees in both directions) were apparent in the middle of the web over the first story height. The damage pattern described above suggested that the web may had initially experienced flexural tension yielding of the boundary steel, followed by buckling of the unsupported web over the relatively short plastic hinge length. The L-shaped cross-section would have resulted in a deep compression zone with high compression strains at the damage end of the web wall. Stability of the compression zone might have been compromised by a reduction in the web out-of-plane bending stiffness due to open flexural tension cracks from previous cycles (Kam et al, 2012). In addition, the vertical reinforcing bars also appear to have buckled more severely outside of the confined boundary zone (refer to picture in page 16). Notice the existence of a cross-tie in the shear wall. This suggests that additional cross-ties may have enhanced the post-yield stability of the wall in addition to the global buckling stability of the wall. On the other hand, some non-structural deformation compatibility damage could be found in the stairwell areas. The severity of shaking had also caused extensive damage to office contents and ceilings.

Summary of causes of damage

The open area around one of the shear walls was likely the main factor contributing to damage. This opening caused the south shear wall to be unable to carry significant earthquake load. Most of the load should have been carried by the north shear wall, which potentially led the north wall to larger demands than it was designed for.Wall slenderness, combined with high overstrength flexural demands caused by the large "flanges" of the V-shaped wall also likely exacerbated demands on the walls.In addition to global out-of-plane wall stability within the plastic hinge zone, it is also likely that a longer boundary zone may have delayed the onset of web buckling and assisted with confining the concrete core of the web.

Observed Design and Construction Characteristics

 

Construction Quality

MaterialsNotesContribution to Damage
Concrete
Reinforcing steel Deformed rebar was used in damage location

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 No evidence of distress to perimeter column elements, which would typically be associated with a torsional response
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 Insufficient collector along the diaphragm

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 Axial load ratio of shear wall

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

NA

Hazard Level

NA

Retrofit or Repair Code

NA

Other Retrofit or Repair Code

Lateral Analysis

NA

Other Lateral Analysis

Design Strategy

Retrofit Summary

References

 

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.


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).


http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/
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).


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