Performance of concrete buildings in the 22 February 2011 Christchurch earthquake and implications for Canadian codes

At 12:51 pm local time on 22 February 2011, a M 6.2 aftershock of the 4 September 2010, Darfield earthquake shook the city of Christchurch, New Zealand. The aftershock occurred on an unmapped fault less than 10 km from the city centre resulting in significant damage, particularly in the Central Business District (CBD). The earthquake resulted in the collapse of two reinforced concrete office buildings, one parking garage, and numerous unreinforced masonry buildings, including many heritage structures, leading to 185 deaths. Liquefaction was wide spread in the CBD and the eastern suburbs, resulting in foundation movement for housing and office buildings alike. Many buildings in the CBD experienced severe damage, some requiring demolition, necessitating careful controlled access to the CBD in the months following the earthquake. This paper summarizes the recorded earthquake shaking and observed damage to concrete buildings in CBD, with a specific focus on identifying future research and possible changes for seismic design practice and codes in Canada to address the Christchurch observations. Key words: earthquakes, collapse, concrete buildings, shear walls, irregularities, precast stairs, deformation compatibility, NBCC. A 12 h 51 heure locale le 22 fevrier 2011, la Ville de Christchurch, Nouvelle-Zelande, a subi une replique sismique d'une magnitude de 6,2 du seisme du 4 septembre 2010 de Darfield. La replique sismique est survenue dans une faille non repertoriee a moins de 10 km du centre-ville, engendrant de graves dommages, particulierement au district des affaires (CBD). Le seisme a cause l'effondrement de deux immeubles a bureaux en beton arme, d'un garage de stationnement et de nombreux immeubles en maconnerie non armee, dont plusieurs batiments patrimoniaux, causant 185 deces. La liquefaction etait etendue dans le CBD et dans les banlieues a l'est, entrainant des mouvements des fondations des maisons et des immeubles a bureaux. Plusieurs immeubles dans le CBD ont subi de graves dommages, certains devant etre demolis, demandant un acces tres controle au CBD pendant les mois suivant le seisme. Le present article resume la secousse sismique enregistree et les dommages observes aux immeubles en beton dans le CBD; il porte une attention speciale a l'identification des recherches futures et aux changements possibles aux pratiques de conception et aux codes sismiques canadiens afin de traiter les observations de Christchurch. Mots-cles : seismes, effondrement, immeubles en beton, murs de refend, irregularites, escaliers prefabrique, compatibilite des deformations, CNBC. [Traduit par la Redaction]
Introduction New Zealand lies at the boundary of the Australian and Pacific tectonic plates, experiencing more than 25 earthquakes over magnitude 6 in the past 10 years (GeoNet 2011). Most [...]