Lisa M. Moon, Dmytro Dizhur, Jason M. Ingham & Michael C. Griffith
Link from: https://researchspace.auckland.ac.nz/bitstream/handle/2292/19768/22_MOON_AEES_2012_Paper.pdf?sequence=2
Abstract
Following the Christchurch earthquake of 22 February 2011 a number of researchers were
sent to Christchurch, New Zealand to document the damage to masonry buildings as part of
“Project Masonry”. Coordinated by the Universities of Auckland and Adelaide, researchers
came from Australia, New Zealand, Canada, Italy, Portugal and the US. The types of
masonry investigated were unreinforced clay brick masonry, unreinforced stone masonry,
reinforced concrete masonry, residential masonry veneer and churches; masonry infill was
not part of this study.
This paper focuses on the progress of the unreinforced masonry (URM) component of Project
Masonry. To date the research team has completed raw data collection on over 600 URM
buildings in the Christchurch area. The results from this study will be extremely relevant to
Australian cities since URM buildings in New Zealand are similar to those in Australia.
INTRODUCTION:
Since the M 7.1 Darfield earthquake on 4 September 2010 the region around Christchurch,
New Zealand, has been subjected to over 10,000 earthquakes on previously unknown fault
lines. The most catastrophic of these was the M 6.3 earthquake on 22 February 2011, which
occurred close to the CBD. Furthermore, between September 2010 and August 2012 the
region was shaken by about 50 earthquakes M 5.0 and above. Figure 1 shows the location of
the 4 September 2010 and 22 February 2011 earthquakes and the location of all aftershocks
M 3.0 or greater up to 11 July 2012. Figure 2 shows the magnitudes of all earthquakes from
4 September 2010 until August 2012. The peak ground accelerations induced in Christchurch
due to the Darfield Earthquake were approximately equal to those of the design level
earthquake, and the only visible shaking damage in the city was sustained by the most
vulnerable known building type: URM buildings. On 22 February, despite the smaller
earthquake magnitude, the accelerations induced in the CBD were up to three times greater
than designed for and while all buildings types sustained some damage from this earthquake,
URM buildings again suffered the most damage.
Christchurch was famous for its many heritage and URM, buildings, so following the 22
February earthquake researchers were dispatched to Christchurch to document the damage to
URM buildings. Later, researchers were also sent to focus study reinforced concrete masonry
(RCM), residential masonry veneer, churches, and stone masonry.
BACKGROUND:
2011 marked the end of a long term study by the University of Auckland into the seismic
assessment and retrofit of URM buildings in New Zealand, which also included a study on
the standard typologies for URM buildings around the country (Retrofit Solutions, 2011). The
study showed that the types of URM buildings around the country were of similar styles and
ages, and that the building stock was relatively homogenous (Russell & Ingham, 2010). The
URM buildings in Christchurch can therefore be considered representative of those across
New Zealand, and therefore their seismic performance during the Christchurch Earthquake
sequence is typical of how all New Zealand URM buildings would respond seismically. In
some cases Christchurch URM buildings had also previously received various levels and
forms of seismic retrofit. Therefore, studying the failure modes of these buildings and the
effectiveness of retrofits can help predict what would happen to URM buildings in other New
Zealand cities and how retrofits are likely to perform.
Engineers from the Universities of Auckland and Adelaide spent time in Christchurch
studying the damage to URM buildings following the 4 September 2010 earthquake, and this
has been reported by Dizhur et al (2010), Griffith et al (2010) and Ingham & Griffith (2011a).
This meant that not only were the team familiar with the Christchurch URM building stock
but that they also had a record of damage to these buildings from before the 22 February
earthquake and could therefore better understand what additional damage was caused by the
February earthquake. Figure 3 shows an example of progressive damage to a URM building
in Christchurch. Figure 3 (a) shows the building fenced off after the 2010 Darfield
earthquake; Figure 3 (b) shows the same building five months later with part of the parapet
fallen and the front wall braced on the left; and Figure 3 (c), taken four days after the 22
February earthquake and six days after Figure 3 (b), shows the loss of the front parapet and
out-of-plane failures of upper walls.
SUMMARY AND CONCLUSIONS:
Project Masonry will result in the creation of a unique database which can be used by the
public, recording the progression of damage to and characteristics of Christchurch’s many
masonry buildings. The database will allow researchers to see the frequency of different
damage modes, and to look for trends in building types and damage types. It will enable the
team to develop fragility curves and scrutinise the performance and effectiveness of different
retrofit techniques. Although the database is not complete preliminary results have been
widely reported, and already it has been shown that buildings must be strengthened to at least
67% of the code requirements for new buildings in order to significantly reduce the
likelihood of suffering major damage.
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