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The progressive damage and subsequent demolition of unreinforced masonry (URM) buildings arising from the Canterbury earthquake sequence is reported. A dataset was compiled of all URM buildings located within the Christchurch CBD, including information on location, building characteristics, and damage levels after each major earthquake in this sequence. A general description of the overall damage and the hazard to both building occupants and to nearby pedestrians due to debris falling from URM buildings is presented with several case study buildings used to describe the accumulation of damage over the earthquake sequence. The benefit of seismic improvement techniques that had been installed to URM buildings is shown by the reduced damage ratios reported for increased levels of retrofit. Demolition statistics for URM buildings in the Christchurch CBD are also reported and discussed.

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As part of the ‘Project Masonry’ Recovery Project funded by the New Zealand Natural Hazards Research Platform, commencing in March 2011, an international team of researchers was deployed to document and interpret the observed earthquake damage to masonry buildings and to churches as a result of the 22nd February 2011 Christchurch earthquake. The study focused on investigating commonly encountered failure patterns and collapse mechanisms. A brief summary of activities undertaken is presented, detailing the observations that were made on the performance of and the deficiencies that contributed to the damage to approximately 650 inspected unreinforced clay brick masonry (URM) buildings, to 90 unreinforced stone masonry buildings, to 342 reinforced concrete masonry (RCM) buildings, to 112 churches in the Canterbury region, and to just under 1100 residential dwellings having external masonry veneer cladding. In addition, details are provided of retrofit techniques that were implemented within relevant Christchurch URM buildings prior to the 22nd February earthquake and brief suggestions are provided regarding appropriate seismic retrofit and remediation techniques for stone masonry buildings.

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The work focuses on the analysis of the seismic response of masonry building aggregates for a better understanding of the vulnerability of single structural units and of their behaviour within the aggregates. Idealized representative models are developed based on the typical characteristics of the row conglomeration typology. The seismic response of the models is evaluated and discussed by means of nonlinear dynamic analyses.

A unidirectional shake-table test was performed on the half-scale prototype of a natural stone masonry building aggregate, to investigate the seismic performance of this type of historical construction and to assess the effectiveness of two retrofit solutions. The specimen represented a building aggregate with two adjacent three-storey units, connected along one side as if they were built at different times. Double-leaf stone masonry with undressed blocks and river pebbles was used for the walls. Timber floors constituted flexible diaphragms in their planes. Roofs with different timber truss configurations and heights covered the two units. Improved wall-to-diaphragm connections and tie rods were pre-installed, although initially not fastened, on the prototype. Both retrofit systems were activated after significant damage was reached testing the unstrengthened specimen. This paper describes the seismic behaviour of the prototype, focusing on the effects of the retrofit interventions on damage mechanism evolution, lateral displacement demand, hysteretic response, and dynamic properties degradation.