Performance of unreinforced masonry buildings during the 2010 Darfi eld (Christchurch, NZ) earthquake
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1
Performance of unreinforced masonry buildings
during the 2010 Darfield (Christchurch, NZ) earthquake*
J Ingham
Department of Civil and Environmental Engineering, University of Auckland, New Zealand
M Griffith†
School of Civil, Environmental and Mining Engineering,
University of Adelaide, South Australia, Australia
ABSTRACT: The 2010 Darfield earthquake caused extensive damage to a number of unreinforced
masonry buildings. While this damage to important heritage buildings was the largest natural
disaster to occur in New Zealand since the 1931 Hawke’s Bay earthquake, the damage was
consistent with projections for the scale of this earthquake, and indeed even greater damage might
have been expected. In general, the nature of damage was consistent with observations previously
made on the seismic performance of unreinforced masonry buildings in large earthquakes, with
aspects such as toppled chimneys and parapets, failure of gables and poorly secured face-loaded
walls, and in-plane damage to masonry frames all being extensively documented. This report on
the performance of the unreinforced masonry buildings in the 2010 Darfield earthquake provides
details on typical building characteristics, a review of damage statistics obtained by interrogating
the building assessment database that was compiled in association with post-earthquake building
inspections, and a review of the characteristic failure modes that were observed. It was observed
that structures that had been seismically retrofitted appeared to perform well, with further study
now required to better document the successful performance of these retrofit solutions.
1 INTRODUCTION have been expected, with associated fatalities and
major casualties. Instead, the single most striking
At 4.35 am on the morning of Saturday 4 September statistic was that there were no fatalities directly
2010, a magnitude 7.1 earthquake occurred associated with the earthquake (although there was
approximately 40 km west of the city of Christchurch, one heart attack fatality and one person hospitalised
New Zealand, at a depth of about 10 km (GNS, 2010), due to a falling chimney (NZ Herald, 2010)); and
having an epicentre located near the town of Darfield. the overall impression is that damage in the central
The ground motion had a peak ground acceleration business district (CBD) was reasonably contained,
(PGA) of about 0.25g and a spectral acceleration in restricted primarily to unreinforced masonry (URM)
the plateau region of about 0.75g, which corresponds buildings, and damage to windows in taller steel
well with the design spectra for a site class D soil and concrete structures. The absence of fatalities
site in Christchurch for spectral periods greater than and more extensive damage is attributed to the
0.2 s. In general, the earthquake represented 67% to comparatively high level of seismic design capability
100% of the design level event, depending upon the in New Zealand, and the fact that the CBD, which
spectral period being considered (see figure 1), with is the region containing the highest density of URM
most of Canterbury reporting damage consistent buildings, was almost completely unoccupied
with MM8 on the Modified Mercalli intensity scale. at 4.35 am. Despite the number of buildings that
Hence, significant damage to earthquake prone had received some form of seismic improvement,
buildings and to non-structural components might a question currently remains as to why a greater
number of URM buildings did not suffer significant
* Reviewed and revised version of paper originally presented damage in the earthquake.
at the 2009 Australian Earthquake Engineering Society
Conference, 11-13 December 2009, Newcastle, NSW. The soil conditions in Christchurch have three
† Corresponding author A/Prof Michael Griffith can be separate material types: river outwash gravels,
contacted at mcgrif@civeng.adelaide.edu.au. sands, and marshy ground in former swamp
© Institution of Engineers Australia, 2011 Australian Journal of Structural Engineering, Vol 11 No 32 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
1.0 N26W component – Cathedral College site
NZSEE Class D Deep or Soft Soil
0.30
Acceleration(g)
Median of Soft Soil Sites
N26W
5% damped Response Spectrum
Botanical Gardens CBGS-H1 0.15
0.8 Botanical Gardens CBGS-H2
Cathedral Collage CCCC-H1 0
Cathedral Collage CCCC-H2
-0.15
Acceleration (g)
Hospital CHHC-H1
0.6 Hospital CHHC-H2 -0.30
0 10 20 30 40 50 60
Time(s)
0.4 N64E component – Cathedral College site
0.30
Acceleration(g)
N64E
0.15
0.2
0
-0.15
0 -0.30
0 1 2 3 4 5 0 10 20 30 40 50 60
(a) Period T(s) (b) Time(s)
Figure 1: Details of earthquake ground motion – (a) acceleration spectra, and
(b) acceleration time-history record (source: GeoNet).
areas, with the central city built mainly on gravels, buildings most widely affected (Page, 1991) and
although there are pockets of sand and soft soil in to date is the only earthquake to have caused any
former marsh deposits. The earthquake ground fatalities in Australia (see figures 2(c) and 2(d)).
motion characteristics shown in figure 1 reflect the • The M6.8 2007 Gisborne (New Zealand)
underlying soil condition, with the long period earthquake caused damage to numerous URM
nature of the motion resulting from the soft soils buildings, including the collapse of 22 parapets
upon which Christchurch is founded. These soft (Davey & Blaikie, 2010). Examples of damage to
soils effectively act as a filter and remove high URM buildings are shown in figures 2(e) and 2(f).
frequency ground motion (leading to smaller
• The M8.8 2010 Maule (Chile) earthquake caused
PGA values than on rock sites), but amplify long
extensive damage to older houses, churches and
period motion, resulting in significantly larger
other buildings constructed of URM or adobe, as
longer period motion at about 2.5 s on several of
shown in figures 2(g) and 2(h) (EERI, 2010).
the softer soil sites. As most URM buildings have
a fundamental period of 0.2-0.3 s, the underlying • The M5.0 2010 Kalgoorlie-Boulder (Australia)
ground conditions appear to have assisted in earthquake occurred near Kalgoorlie-Boulder,
reducing the seismic demand in this period range causing damage to historic buildings in the city
to approximately 70% of the current NZS 1170.5 (see figures 2(i) and 2(j)). There were no fatalities,
(Standards New Zealand, 2004) design level loading but two people were treated at Kalgoorlie
for a site class D soil site in Christchurch. Hospital for minor injuries resulting from the
earthquake (Edwards et al, 2010).
As can be seen in figure 1(b), strong ground shaking
in the CBD had a duration of approximately 30 s, with An initial evaluation procedure (IEP) is provided
similar amplitudes in the two orthogonal recording in NZSEE (2006) as a coarse screening method for
directions. This lack of distinct directionality determining a building’s expected performance in
probably explains why parapet failures were an earthquake. The purpose of the IEP is to make an
observed in streets running in both the north-south initial assessment of the performance of an existing
and east-west directions. building against the standard required for a new
building, ie. to determine the “Percentage New
Building Standard” (%NBS). A %NBS of 33 or less
2 BACKGROUND means that the building is assessed as potentially
earthquake prone in terms of the Building Act (New
It is well established that URM buildings perform Zealand Parliament, 2004) and a more detailed
poorly in large magnitude earthquakes, with a brief evaluation will then typically be required. A %NBS
selection of relevant prior earthquakes that have of greater than 33 means that the building is regarded
caused major damage to URM buildings being as outside the requirements of the Act, and no further
detailed below: action will be required by law, although it may still
• The M7.8 1931 Hawke’s Bay (New Zealand) be considered as representing an unacceptable risk
earthquake caused widespread devastation to and seismic improvement may still be recommended
URM buildings in the city of Napier (see figures (defined by the New Zealand Society for Earthquake
2(a) and 2(b)), with 256 fatalities. This earthquake Engineering (NZSEE) as potentially “earthquake
remains the worst disaster of any type to occur risk”). A %NBS of 67 or greater means that the
on New Zealand soil (Dowrick, 1998). building is not considered to be a significant
earthquake risk. NZSEE noted that:
• The M5.6 1989 Newcastle (Australia) earthquake
resulted in 13 fatalities and over 160 casualties. A %NBS of 33 or less should only be taken as
The earthquake damaged approximately 50,000 an indication that the building is potentially
buildings (80% of these were homes) with URM earthquake prone and a detailed assessment may
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 3
(a) (b)
(c) (d)
(e) (f)
(g) (h)
(i) (j)
Figure 2: Representative examples of damage to URM buildings in past earthquakes – (a) overlooking
Napier at the buildings destroyed by the 1931 earthquake and fires (source: Alexander
Turnbull Library); (b) view down Hastings Street, Napier, after the 1931 earthquake (source:
Alexander Turnbull Library); (c) out-of-plane wall failure in the 1989 Newcastle earthquake;
(d) parapet and cavity wall damage in the 1989 Newcastle earthquake; (e) toppled parapet
in the 2007 Gisborne earthquake; (f) out-of-plane failure of a gable wall in the 2007 Gisborne
earthquake; (g) 1940s URM house, Maipu Street, Concepcion, Chile (source: Andrea Garcia);
(h) Barros Arana Institute, Barros Arana corner with Angol, Concepcion, Chile (source: Andrea
Garcia); (i) damage to parapet and awning in Boulder; and (j) toppled parapet in Boulder.
Australian Journal of Structural Engineering Vol 11 No 34 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
well show that a higher level of performance is and Australia are evident by comparing the images
achievable. The slight skewing of the IEP towards shown in figure 2. A common architectural feature is
conservatism should give confidence that a building for passing pedestrians to be covered by an overhead
assessed as having a %NBS greater than 33 by awning that is located at the height of the first floor,
the IEP is unlikely to be shown, by later detailed which is typically braced back to the piers of the
assessment, to be earthquake prone. second floor. Figure 3 shows this detail.
Recent research has suggested that there are Post-earthquake inspection of building performance
approximately 3750 URM buildings in New Zealand led to 595 URM buildings being assessed, out of the
(Russell & Ingham, 2010), with their distribution 958 URM buildings reported to exist in Christchurch.
throughout New Zealand being aligned with the It is believed that the majority of unassessed URM
relative prosperity of communities during the buildings were undamaged and outside the primary
period between approximately 1880 and 1930. inspection zone associated with the CBD and arterial
Following the Darfield earthquake, it was reported routes extending from the central city. General
that the Canterbury region had approximately features of the 595 assessed URM buildings are
7600 earthquake-prone buildings, with 958 of these reported in figure 4, indicating that the majority of
buildings being constructed of URM (Christchurch buildings were either 1- or 2-storey, consistent with
City Council, 2010; Wells, 2010). prior findings by Russell & Ingham (2010). Figure
4(c) shows that the most common occupancy type
3 ARCHITECTURAL CHARACTER was commercial or office buildings, and hence the
majority of buildings were unoccupied at the time
The architectural features of the URM building of the earthquake, significantly contributing to the
stock in the Canterbury region of New Zealand are lack of direct earthquake fatalities. The survey forms
consistent with the general form of URM buildings contained a field to record the estimated gross floor
throughout both New Zealand and Australia area of the building, and hence the estimated building
(Russell & Ingham, 2008; 2010). These buildings footprint could be determined once accounting for
can be characterised as typically 2 or 3 storeys in the number of storeys (see figure 4(b)), but the data
height, with 2-storey buildings being most common, is unfortunately incomplete as only 301 entries were
and being either stand-alone or row buildings, recorded for the 595 separate buildings assessed. It is
but with row buildings being most common (refer not possible to establish from the database whether
figure 3). In particular, similarities in architectural individual entries belonged to a stand-alone or a
character between URM buildings in New Zealand row building.
(a) (b)
(c) (d)
Figure 3: Pre-earthquake examples of typical URM building architecture in Christchurch –
(a) 188 Manchester Street; (b) corner of Sandyford and Colombo Street; (c) 118 Manchester
Street; and (d) corner of Colombo and Tuam Street.
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 5
501ч ч50
13% 11%
Other Public Religious
3+Storey residential
17% assembly 2%
7% 5%
1Storey
29% Other
Industrial 3%
2%
51Ͳ100
Heritage
201Ͳ500 24% Listed
25% 3%
Dwelling
11%
Commercial
2Storey /Offices
101Ͳ200
(a) 54%
(b) 27% (c) 67%
Figure 4: Building characteristics derived from interrogation of the inspection database – (a) storey
height (595 entries); (b) footprint area (m2; 301 entries); and (c) occupancy type (595 entries).
(a) (b)
Figure 5: Masonry rubble from collapsed wall – (a) masonry rubble showing “clean” bricks;
and (b) weak mortar crumbles between fingers.
(a) (b)
Figure 6: Large sections of masonry intact after fall from buildings – (a) solid section
of masonry gable; and (b) solid section of parapet.
4 MATERIAL PROPERTIES centre of the wall facing the street, as this segment
of the collapsed parapet often remained intact as it
The general observation from the debris of collapsed collapsed (refer figure 6).
URM walls was that the kiln-fired clay bricks were
generally of sound condition, but that the mortar was
in poor condition. In most cases the fallen debris had 5 BUILDING DAMAGE STATISTICS
collapsed into individual bricks, rather than as larger
chunks of masonry debris (refer to figure 5(a)). When In general, the observed damage to URM buildings
rubbing the mortar that was adhered to bricks it was in the 2010 Darfield Earthquake was consistent with
routinely found that the mortar readily crumbled the expected seismic performance of this building
when subjected to finger pressure (refer figure 5(b)), form, and consistent with observed damage to URM
suggesting that the mortar compression strength was buildings both in past New Zealand and Australian
very low. However, it appears that superior mortar earthquakes and in numerous earthquakes from other
was often used in the ornate parapet above the countries (see figure 2). As part of the emergency
Australian Journal of Structural Engineering Vol 11 No 36 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
response to this earthquake, the authors spent 72 than 10% damage. It was also possible to study the
hours assisting Christchurch City Council with distribution of damage dependent on storey height
building damage assessments, tagging buildings (figure 8(c)), with the data indicating no definitive
with either a green, yellow or red placard depending, trend and a comparatively uniform level of damage
respectively, upon whether a building was safe for assigned to buildings in each height category.
public use, had limited accessibility for tenants/
occupants, or was not accessible (refer to figure
6 CHIMNEYS
7). Many examples of earthquake damage were
observed during this exercise, as well as many
Unsupported or unreinforced brick chimneys
examples of seismic retrofits to URM buildings that
performed poorly in the earthquake (figure 9),
had performed well.
with numerous chimney collapses occurring in
The results from the interrogation of damage domestic as well as small commercial buildings and
assessment information are reported in figure 8. some churches. Many examples of badly damaged
Figure 8(a) reports the “useability” assignment of the chimneys that were precariously balanced on rooftops
595 URM buildings assessed. In consultation with were also seen (figure 9(b)) and it was reported that
staff of Christchurch City Council it is believed that one week after the earthquake, 14,000 insurance
the complement of the 958 URM buildings thought claims involving chimney damage had been received,
to exist in Christchurch probably had a green tag from a total of 50,000 claims (NewstalkZB, 2010).
usability rating, and so this theorised damage Emergency services personnel were in significant
distribution for the entire URM building stock is demand, being deployed to remove damaged
shown in figure 8(b). chimneys in order to minimise further risk and
eliminate these “falling hazards” (figure 9(c)). In
Figure 8(c) reports the level of damage for the
contrast, figure 9(d) shows an example of a braced
595 buildings that were surveyed by the Rapid
chimney that performed well. Note that figure 9(b)
Building Assessment teams. No explicit definitions
shows further evidence of the poor performance of
were provided to the assessment teams for what
mortar during the earthquake.
represented and range (%) damage. The values
recorded by the teams for each building surveyed
were simply estimates (excluding contents damage). 7 GABLE END WALL FAILURES
Despite the known vulnerability of URM buildings
to earthquake loading, 395 of the 595 buildings (66%) Many gable end failures were observed, often
were rated as having 10% damage or less, with only collapsing onto or through the roof of an adjacent
162 (34%) of the buildings assessed as having more building (refer figures 9(a) and 10). However, there
(b)
(c)
(a) (d)
Figure 7: Building assessment notices – (a) Urban Search And Rescue personnel applying an
assessment notice; (b) green tag; (c) yellow tag; and (d) red tag.
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 7
Red
Red 13%
21%
Yellow
Green 17%
47%
Green
Yellow 70%
(a) 32% (b)
30% 180
Unknown
3+StoreysHigh
PercentageofBuildingsSurveyed
NumberofBuildingsSurveyed
24% 2StoreysHigh 144
1StoreyHigh
18% 108
12% 72
6% 36
0% 0
none 0Ͳ1% 2Ͳ10% 11Ͳ30% 31Ͳ60% 61Ͳ99% notspec
(c) ExtentofDamagetoBuilding
Figure 8: Damage statistics – (a) distribution of placard assignments (595 entries);
(b) theorised damage distribution for entire building stock (958 entries);
and (c) extent of building damage.
(a) (b)
(c) (d)
Figure 9: Examples of chimney performance during the Darfield earthquake – (a) two damaged
chimneys and gable wall; (b) unstable damaged chimney; (c) emergency service workers
remove chimney; and (d) braced chimney performed well.
Australian Journal of Structural Engineering Vol 11 No 38 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
(a) (b)
(c) (d)
Figure 10: Examples of gable end wall failures – (a) 93 Manchester St; (b) 816 Colombo St;
(c) Montreal-Armagh street corner; and (d) Kilmore-Montreal street corner.
were also many gable ends that survived; many more at the wall end that is about 50 mm wide × 450 mm
than might have been expected, with the majority long, and fastened to the rod and positioned either
having some form of visible restraints that tied back inside the brick wall or in the centre of a masonry pier
to the roof structure. These examples are shown and or wall. In most cases the force on the rod exceeded
discussed later (refer figures 17-18). the capacity of the masonry wall anchorage, causing a
punching shear failure in the masonry wall identified
by a crater in the masonry (refer figure 12(a)).
8 PARAPET FAILURES
Numerous parapet failures were observed along 10 WALL FAILURES
both the building frontage and along their side
walls, and for several URM buildings located on the Out-of-plane wall failures were the first images to
corners of intersections, the parapets collapsed on appear on television directly after the earthquake.
both perpendicular walls (refer figure 11). Restraint Inspection of this damage typically indicated poor
of URM parapets against lateral loads has routinely or no anchorage of the wall to its supporting timber
been implemented since the 1940s, so while it is diaphragm. Several examples of wall failure are
difficult to see these restraints unless roof access is shown in figure 13. Figure 13(a) shows a corner
available, it is believed that the majority of parapets building that had walls fail in the out-of-plane
that exhibited no damage in the earthquake were direction along both directions. Figure 13(b) shows
provided with suitable lateral restraint. In several a 3-storey building where walls in the upper two
cases, it appears that parapets were braced back to the storeys suffered out-of-plane failures and figure 13(c)
perpendicular parapet, which proved unsuccessful. shows similar damage for a 2-storey building. In all
three of these instances, it appears that the walls
were not carrying significant vertical gravity loads,
9 ANCHORAGE FAILURES
other than their self weight, due to the fact that the
remaining roof structures appear to be primarily
Falling parapets typically landed on awnings,
undamaged. In contrast, figure 13(d) shows an out-
resulting in an overloading of the braces that
of-plane failure of a side wall that was supporting
supported these awnings and leading to collapse.
the roof trusses prior to failure.
Most awning supports in Christchurch involved a
tension rod tied back into the building through the As shown in figure 14, several examples of face load
front wall of the building. Many of these connections wall failure closely resembled observed damage in
appear to consist of a long, roughly 25 mm diameter dry stack masonry experiments (Restrepo-Velez &
rod, with a rectangular steel plate (about 5 mm thick) Magenes, 2009), providing further support to the
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 9
(a) (b)
(c) (d)
Figure 11: Examples of typical parapet failures – (a) multiple front wall parapet failures; (b) corner of
Sandyford and Colombo Street (see also figure 3(b)); (c) side wall parapet collapse onto roof;
and (d) corner Columbo and Tuam Street (see also figure 3(d)).
(a) (b)
Figure 12: Anchorage failure of awning brace due to parapet collapse – (a) anchorage failure;
and (b) close-up of failed anchorage detail.
(a) (b)
(c) (d)
Figure 13: Examples of out-of-plane failures in solid masonry walls – (a) corner Worcester and
Manchester streets (see also figure 3(a)); (b) 118 Manchester Street (see also figure 3(c));
(c) 179 Victoria Street; and (d) out-of-plane failure of a side wall that was supporting the
roof trusses prior to failure.
Australian Journal of Structural Engineering Vol 11 No 310 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
(a) (b)
Figure 14: Failure mechanism comparisons (observed earthquake damage versus experimental
simulation) – (a) wall damage at 140 Linchfield Street; and (b) high speed photograph
of a dry-stacked masonry wall failing during a tilt test.
(a) (b)
(c) (d)
Figure 15: Examples of out-of-plane failures in cavity walls – (a) cavity wall failure in a residential
building; (b) 832 Columbo Street; (c) butterfly wall ties still intact; and (d) metal wall ties
badly deformed.
supposition that many of the wall failures were partly In some cases wall-diaphragm anchors remained
attributable to poor mortar strength. visible in the diaphragm after the wall had failed,
again indicating that failure had occurred due to
Cavity wall construction is generally believed to be
bed joint shear in the masonry (refer figure 16(a)).
much less common in New Zealand than is solid
Figure 16(b) shows a situation where a diaphragm
multi-leaf (or multi-wythe) construction. However,
anchor had been embedded within the wall. It can
cavity wall construction can be extremely vulnerable
be seen that the anchor successfully prevented the
to out of plane failure in earthquakes in situations
restrained wall from failing, but was not able to
where the cavity ties were poorly installed, or more
prevent toppling of the parapet that was located
commonly have corroded over time, as the wall is
above the anchor.
then comparatively slender and less stable than for
solid construction. Figures 15(a) and 15(b) show
examples of cavity wall buildings that suffered out- 11 SUCCESSFUL WALL ANCHORAGE
of-plane wall failures. Figures 15(c) and 15(d) show
that cavity ties were present but were insufficient to A significant feature of the earthquake was the
prevent the outer leaf from failing. number of occasions where anchored walls performed
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 11
(a) (b)
Figure 16: Wall-to-diaphragm anchor details – (a) gable end wall failure despite anchor
(see also figure 13(a)); and (b) wall anchor still intact (see also figure 6(a)).
Figure 17: Successful gable end wall and side wall anchorages on an arts centre building.
(a) (b)
Figure 18: Successful wall-floor and wall-roof diaphragm anchorages – (a) front elevation;
and (b) side elevation.
well during the earthquake. Photographs showing 13 PARTIAL WALL FAILURES
this are presented in figures 17-18. A typical wall-to-
diaphragm (roof or floor) anchor typically consists of Another interesting feature of this earthquake is
a long 20 mm bolt with a large circular disc of about the observation of walls that only partly failed,
150-200 mm diameter between the wall exterior and allowing for identification of the specific failure
nut that clamped the disc to the wall. This detail is mode at its onset. Several excellent examples are
shown quite clearly in figure 16(a). described below. The first of these is a 2-storey URM
building on Ferry Road (see figure 20), where the
12 IN-PLANE WALL FAILURES front, street facing, wall of the building had started
to fail out-of-plane despite the presence of wall-roof
Where walls exhibited some damage to in-plane diaphragm anchors. As is shown, the anchors were
deformation the cracks were mostly seen to pass on the verge of pulling through the masonry wall.
vertically through the lintels over door or window Internal inspection of the building revealed that the
openings. Examples are shown in figure 19. However, front wall had separated from the long side walls
this type of damage was not widely observed. of the building and moved approximately 50 mm
Australian Journal of Structural Engineering Vol 11 No 312 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
(a) (b)
(c) (d)
Figure 19: Examples of in-plane wall damage above window openings – (a) extensive vertical cracking
above window openings; (b) vertical crack above window opening; (c) vertical crack through
spandrel; and (d) diagonal crack extending from window opening.
(a) (b)
(c) (d)
Figure 20: Wall-roof anchorage failure and partial wall failure – (a) building overview;
(b) detail of partial anchorage failure; (c) onset of anchorage failure; and
(d) internal view showing wall separation.
towards the road with respect to the ceiling/roof earthquake not imposing sufficient displacement on
diaphragm (figure 20(d)). It is believed that due to the the wall after the anchorage failure.
nature of strength degradation of the brickwork at the A similar style of partial failure was observed in
onset of a punching shear failure, the anchorage has another building on Ferry Road (figure 21(a)) but
effectively failed and offers little residual resistance the authors were only able to observe the building
against further shaking. The only reason the wall externally. It should be noted that the buildings were
did not completely collapse is probably due to the not in close proximity to each other. An example
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 13
(a) (b)
Figure 21: Partial bed joint shear failure surrounding anchorage detail – (a) wall-roof anchorage failure;
and (b) gable end anchorage failure.
(a) (b)
Figure 22: Examples of yielded wall anchors – (a) overview of wall anchors; and
(b) close-up view of yielded anchor.
of a gable end partial failure is shown in figure damage is not necessarily a catastrophic problem if
21(b), which can be compared to the comparable stiff horizontal diaphragms are well connected to
anchorage detail shown in figure 16(a) that resulted the walls in both directions, but where there is not
in complete failure. good diaphragm connectivity, there is the potential
There were frequent examples of wall-diaphragm for complete out-of-plane collapse of one or both
anchors that had deformed plastically. In these walls. Figure 24 shows some examples where major
photographs (figure 22), the circular plate can be seen cracking was observed between the side return walls
to be slack due to plastic stretching of the anchor rod. and the front parapet and wall.
14 DIAPHRAGM DEFORMATIONS 16 POUNDING
There was one instance where it was clear that Several instances of damage due to buildings
diaphragm deformation, relative to the in-plane pounding against each other during the earthquake
walls, contributed to partial failure of an out-of-plane were observed. Figure 25 shows how the shorter
wall. Figure 23 shows several views of a building that building in the centre, which has different floor
suffered out-of-plane parapet failure along its long, heights than the building to the left, damaged the
side walls. In figure 23(b) it can be seen that the roof column of the taller building at its top storey.
joists have tilted towards the front of the building.
This suggested that the front wall of the building
17 SPECIAL BUILDINGS
was driven forward at its top. Careful inspection of
the front wall (figure 23(c)) revealed a substantial
160 Manchester Street is a 7-storey office building
outwards curvature that was most pronounced at
that is reported to consist of load bearing masonry
the top.
and is the most significant masonry building, at least
in terms of height, in Christchurch (figure 26). It is
15 RETURN WALL SEPARATION a registered heritage building and is a significant
part of the fabric of the Christchurch city landscape.
Many buildings exhibited substantial cracking Unfortunately, the building suffered significant
between their front wall and side (return) walls. This damage in the earthquake. The bottom two storeys
Australian Journal of Structural Engineering Vol 11 No 314 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
(a)
(b) (c)
Figure 23: Example of diaphragm deformation causing out-of-plane wall failure –
(a) overview of building; (b) side-view of tilted joists; and (c) front wall curvature.
(a) (b) (c)
Figure 24: Examples of wall separation at corners of buildings.
(a) (b) (c)
Figure 25: Example of building pounding damage – (a) building overview;
and (b) and (c) close-up of column.
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 15
are reported to be reinforced concrete, while the pier on the western face of the building to reveal that
top five storeys are reported to have load bearing the external cracking continued through the entire
URM piers around the exterior of the building and pier thickness.
a steel frame internally (columns spaced roughly at
Two days after the main earthquake, structural
5 m) with timber floors throughout (New Zealand
engineers met with Urban Search and Rescue Team
Historic Places Trust, 2010). The masonry piers,
leaders and city officials to determine a strategy
having dimensions of approximately 1200 × 900 mm,
for making the structure safe enough for building
were badly cracked at levels 3 and 4 (figure 27).
contractors and engineers to enter to determine more
This damage was most likely due to the transition
fully the extent of damage and the viability of repair.
from concrete to masonry at level 3 and the fact
Four days after the main earthquake, the building
that the adjoining 2-storey building located along
had survived one M5.4 and three M5.1 aftershocks.
the southern wall side stopped providing lateral
At the time of writing, no decision had been made
support at that level. It appears that the lift core had
as to whether the building will be demolished or
received some strengthening previously, as well as
the roof, perhaps in the late 1980s as reported by the repaired. Currently the building poses a significant
New Zealand Historic Places Trust (2010). Close up falling hazard for people, traffic and buildings
photographs of the masonry piers at levels 3 and located within 70 m in all four directions. This falling
4 show the primary damage that concerned the hazard has resulted in all the buildings within this
assessment teams (figure 27). Further inspection by distance being closed to the public (red-tagged) as
the assessment team exposed the internal face of one well as both main streets (Manchester and Hereford)
that run adjacent to the building.
St Elmo Chambers is also a 7-storey building,
reported to be a reinforced concrete frame building
with external clay brick masonry piers. Owing to the
absence of control joints between the masonry and
concrete frame, it appears that the masonry piers
attracted sufficient seismic in-plane forces to cause
shear failure (refer figure 28). However, once the
masonry cracked the seismic loads were transferred to
the concrete frame. Judging by the extent of cracking
in the brickwork, it appears that the storey drifts were
less than 1%, implying that the concrete frame was not
pushed to its maximum capacity (strength or drift).
The authors were not able to inspect the building from
inside. From external inspection, the building was
judged to pose a falling hazard to pedestrians near
the building, but was in little danger of the building
itself collapsing in an aftershock.
18 BUILDING DAMAGE DUE
TO GROUND DEFORMATION
Figure 26: Manchester Courts Building (view Perhaps the most striking aspect of this earthquake
from northwest). overall was the extensive amount of liquefaction
(a) (b)
Figure 27: Damage to masonry piers at levels 3-5 – (a) north wall piers, levels 3-4;
and (b) west wall piers, levels 4-5.
Australian Journal of Structural Engineering Vol 11 No 316 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
(a) (b)
Figure 28: Views of St Elmo Chambers building in Montreal Street – (a) overview of building;
and (b) close-up of damage to brickwork.
(a) (b)
(c) (d)
Figure 29: Damage to buildings having masonry veneer over timber frame, due to ground deformation
and liquefaction – (a) damage to masonry veneer due to ground deformation; (b) wide
cracks due to ground deformation; (c) masonry veneer damage to recently built residence;
and (d) damage due to liquefaction.
and ground deformation that occurred. These 19 CLOSING REMARKS
phenomena were not seen to a significant extent in
the Christchurch CBD region containing the highest On the few occasions that building owners or
density of URM buildings, but did impact on a occupants were in attendance it was possible to
number of timber-framed structures with masonry gain access to the interior of URM buildings and
veneer. As shown in figure 29, several cases of often observe that some separation had occurred
extreme ground deformation were observed, and between the floor and/or roof diaphragms and the
there were numerous cases where large crack widths masonry walls (in the out-of-plane direction). This
formed in residential timber framed structures damage was not easy to detect from the outside of a
having a masonry veneer (figure 29(c)). There were building, so that the damage reported from building
also cases where ground liquefaction had resulted surveys in the first 72 hours can safely be assumed
in masonry structures having sunk into the ground to be a lower bound estimate of structural damage
(figure 29(d)). to URM buildings.
Australian Journal of Structural Engineering Vol 11 No 3“Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith 17
There were many instances of buildings that were images/eeri_newsletter/2010_pdf/Chile10_insert.
structurally sound themselves, but had suffered pdf, retrieved 16 September 2010.
damage or were yellow or red-tagged owing to
“falling hazards” from neighbouring buildings. GNS, 2010, “Darfield earthquake damages
In some instances it was clear that a parapet or Canterbury”, www.geonet.org.nz/news/article-sep-
chimney from a neighbouring building had fallen 4-2010-christchurch-earthquake.html, 16 September,
onto or through the roof, being the only damage to retrieved 16 September 2010.
the structure. In other instances, a building abutting New Zealand Historic Places Trust, 2010, “Manchester
a taller building with damaged parapet or gable Courts”, www.historic.org.nz/TheRegister/
side walls or chimney was given a yellow card RegisterSearch/RegisterResults.aspx?RID=5307;
(no public access) due only to the falling hazard retrieved 9 September 2010.
posed by the structure next door. These examples of
“collateral damage and risk”, such as that posed by New Zealand Parliament, 2004, Building Act 2004,
160 Manchester Street, and the associated business Department of Building and Housing – Te Tari
interruption costs, will surely make the financial Kaupapa Whare, Ministry of Economic Development,
impact of this earthquake much greater than just the New Zealand Government, Wellington, New
cost of rebuilding. Zealand, date of assent 24 August 2004.
NewstalkZB, 2010, “Most damage claims over
ACKNOWLEDGEMENTS $10k”, www.newstalkzb.co.nz/newsdetail1.
asp?storyid=182291, 13 September, retrieved 13
Rodney Henderson-Fitzgerald, a data analyst September 2010.
for Christchurch City Council, is thanked for his
assistance with securing the building inspection NZ Herald, 2010, “Christchurch earthquake victim: ‘I
data reported herein. Lisa Moon and Najif Ismail was pinned to the ground’”, www.nzherald.co.nz/
are thanked for their analysis and graphing of the nz/news/article.cfm?c_id=1&objectid=10673369; 14
building damage statistics. Dmytro Dizhur, Yi-Wei September, retrieved 20 September 2010.
Lin, Alistair Russell, Charlotte Knox and Claudio
NZSEE, 2006, “Assessment and Improvement of the
Oyarzo-Vera are thanked for supplying some of the
Structural Performance of Buildings in Earthquakes”,
photographs that have been used herein.
Recommendations of a NZSEE Study Group on
Earthquake Risk Buildings, New Zealand Society
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Davey, R. A. & Blaikie, E. L. 2010, “Predicted and
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Australian Journal of Structural Engineering Vol 11 No 318 “Performance of unreinforced masonry buildings during the 2010 Darfield ...” – Ingham & Griffith
JASON INGHAM
Jason Ingham is Associate Professor in the Department of Civil and
Environmental Engineering at the University of Auckland. Jason obtained his
PhD from the University of California at San Diego in 1995, having previously
completed his BE (Hons) and ME (Dist) from the University of Auckland.
Jason also has an MBA from the University of Auckland. Jason is currently
on the management committees of the New Zealand Society of Earthquake
Engineering and the Structural Engineering Society of New Zealand, and is
currently vice-president of the New Zealand Concrete Society. Jason’s primary
research interests are associated with seismic assessment and retrofit of concrete
and masonry structures, and sustainable concrete technology. Over the last 6
years Jason has led a project considering the seismic assessment and retrofit
of unreinforced masonry buildings, with further details available at www.
retrofitsolutions.org.nz.
MICHAEL GRIFFITH
Michael Griffith is Professor in the School of Civil, Environmental and Mining
Engineering at the University of Adelaide. He obtained his PhD in Structural
Engineering from the University of California at Berkeley (1988) after completing
his BSc (Eng) and MSc (Eng) degrees in Civil Engineering at Washington
State University in the US. Michael is a member of the Standards Australia
Australian Earthquake Loading Code committee, and he is also a member of
Engineers Australia, state committee member of the SA Structural College and
Past-President of the Australian Earthquake Engineering Society. His main
professional and research interests are in the field of earthquake engineering
and structural dynamics. He has co-authored two book chapters and over 100
research papers in the field of structural engineering.
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