The city of Christchurch has experienced over 10,000 aftershocks since the 4th of September 2010 earthquake of which approximately 50 have been greater than magnitude 5. The damage caused to URM buildings in Christchurch over this sequence of earthquakes has been well documented. Due to the similarity in age and construction of URM buildings in Adelaide, South Australia and Christchurch (they are sister cities, of similar age and heritage), an investigation was conducted to learn lessons for Adelaide based on the Christchurch experience. To this end, the number of URM buildings in the central business districts of both cities, the extent of seismic strengthening that exists in both cities, and the relative earthquake hazards for both cities were considered. This paper will report on these findings and recommend strategies that the city of Adelaide could consider to significantly reduce the seismic risk posed by URM buildings in future earthquake.
The city of Christchurch, New Zealand, was until very recently a “Junior England”—a small city that still bore the strong imprint of nineteenth-century British colonization, alongside a growing interest in the underlying biophysical setting and the indigenous pre-European landscape. All of this has changed as the city has been subjected to a devastating series of earthquakes, beginning in September 2010, and still continuing, with over 12,000 aftershocks recorded. One of these aftershocks, on February 22, 2011, was very close to the city center and very shallow with disastrous consequences, including a death toll of 185. Many buildings collapsed, and many more need to be demolished for safety purposes, meaning that over 80 percent of the central city will have gone. Tied up with this is the city’s precious heritage—its buildings and parks, rivers, and trees. The threats to heritage throw debates over economics and emotion into sharp relief. A number of nostalgic positions emerge from the dust and rubble, and in one form is a reverse-amnesia—an insistence of the past in the present. Individuals can respond to nostalgia in very different ways, at one extreme become mired in it and unable to move on, and at the other, dismissive of nostalgia as a luxury in the face of more pressing crises. The range of positions on nostalgia represent the complexity of heritage debates, attachment, and identity—and the ways in which disasters amplify the ongoing discourse on approaches to conservation and the value of historic landscapes.
The connections between walls of unreinforced masonry (URM) buildings and flexible timber diaphragms are critical building components that must perform adequately before desirable earthquake response of URM buildings may be achieved. Field observations made during the initial reconnaissance and the subsequent damage surveys of clay brick URM buildings following the 2010/2011 Canterbury, New Zealand earthquakes revealed numerous cases where anchor connections joining masonry walls or parapets with roof or floor diaphragms appeared to have failed prematurely. These observations were more frequent for the case of adhesive anchor connections than for the case of through-bolt connections (i.e. anchorages having plates on the exterior façade of the masonry walls). Subsequently, an in-field test program was undertaken in an attempt to evaluate the performance of adhesive anchor connections between unreinforced clay brick URM walls and roof or floor diaphragm. The study consisted of a total of almost 400 anchor tests conducted in eleven existing URM buildings located in Christchurch, Whanganui and Auckland. Specific objectives of the study included the identification of failure modes of adhesive anchors in existing URM walls and the influence of the following variables on anchor load-displacement response: adhesive type, strength of the masonry materials (brick and mortar), anchor embedment depth, anchor rod diameter, overburden level, anchor rod type, quality of installation and the use of metal foil sleeve. In addition, the comparative performance of bent anchors (installed at an angle of minimum 22.5o to the perpendicular projection from the wall surface) and anchors positioned horizontally was investigated. Observations on the performance of wall-to-diaphragm connections in the 2010/2011 Canterbury earthquakes and a snapshot of the performed experimental program and the test results are presented herein. http://hdl.handle.net/2292/21050
