Damage to concrete buildings with precast floors during the 2016 Kaikoura earthquake

The 2016 Kaikoura earthquake resulted in shaking in excess of design level demands for buildings with periods of 1-2s at some locations in Wellington. This period range correlated to concrete moment frame buildings of 5-15 storeys, many of which had been built in Wellington since the early 1980s, and often with precast concrete floor units. The critical damage states used to assess buildings during the Wellington City Council Targeted Assessment Programme are described and examples of observed damage correlating to these damage states are presented. Varying degrees of beam hinging were observed, most of which are not expected to reduce the frame capacity significantly. Buildings exhibiting varying degrees of residual beam elongation were observed. Cases of significant beam elongation and associated support beam rotation resulted in damage to precast floor unit supports; in one case leading to loss of support for double-tee units. The deformation demands also resulted in damage to floor diaphragms, especially those with hollowcore floor units. Cracking in floor diaphragms was commonly concentrated in the corners of the building, but hollowcore damage was observed both at the corners and in other locations throughout several buildings. Transverse cracking of hollowcore floor units was identified as a particular concern. In some cases, transverse cracks occurred close to the support, as is consistent with previous research on hollowcore floor unit failure modes. However, transverse cracks were also observed further away from the support, which is more difficult to assess in terms of severity and residual capacity. Following the identification of typical damage, attention has shifted to assessment, repair, and retrofit strategies. Additional research may be required to determine the reduced capacity of cracked hollowcore floor units and verify commonly adopted repair and retrofit strategies.

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