Response of instrumented buildings under the 2016 Kaikoura earthquake

Abstract

Six buildings in the Wellington region and the upper South Island, instrumented as part of the GeoNet Building Instrumentation Programme, recorded strong motion data during the 2016 Kaikoura earthquake. The response of two of these buildings: the Bank of New Zealand (BNZ) Harbour Quays, and Ministry of Business, Innovation, and Employment (MBIE) buildings, are examined in detail. Their acceleration and displacement response was reconstructed from the recorded data, and their vibrational characteristics were examined by computing their frequency response functions. The location of the BNZ building in the CentrePort region on the Wellington waterfront, which experienced significant ground motion amplification in the 1–2 s period range due to site effects, resulted in the imposition of especially large demands on the building. The computed response of the two buildings are compared to the intensity of ground motions they experienced and the structural and nonstructural damage they suffered, in an effort to motivate the use of structural response data in the validation of performance objectives of building codes, structural modelling techniques, and fragility functions. Finally, the nature of challenges typically encountered in the interpretation of structural response data are highlighted.

Unexpected Seismic Damage vs. SLS Building Code Anomalies

“…Furthermore, the extent of severe EQ damage or demolition in more than 72 mid-rise buildings in the Wellington CBD due to the small to moderate November 14 2016 ground motions from the distant Kaikōura earthquake raises concerns about the SLS limit designed for these buildings being inadequate in terms of both elastic strength and stiffness [6].…”

“…The extent of reported seismic damage due to small and moderate CBD ground motions in NZ from 2010 to 2016 [1][2][3][4][5][6][7] suggests that the NZ SLS design limit is specified as too small. Disruptive seismic damage has occurred recently in urban NZ, and will continue at frequent intervals.…”

“…The MBIE building in Wellington on class C soil [6], had a calculated period of 0.8 seconds and experienced a PGA of approximately 0.2G. It is shown in Figure 1 that a maximum peak floor acceleration of 0.4G was recorded at its uppermost level.…”

“…This compares with the similar 25 year SLS design SA of 0.16G to 0.23G at ductility of 1.0 for SLS at a range of Sp = 0.7-1.0. [6]. Figures 7 and 8 show the recorded ground motions from the 2016 seismic event on assumed soft class D soils -or very soft class E or Thorndon Basin soils, are shown in to be approximately 50 percent larger than the 25 year SLS event with Sp = 0.7 ('mini-SLS').…”

“…However, the large monetary losses and disruption from small and moderate seismic events has been crippling. The 2010-2011 sequence of Canterbury earthquakes left the community with more than $NZD40 billion in losses (20% GDP), demolition of approximately 60% of multi-storey concrete buildings (3 storeys and up,) and closure of the Core Business District (CBD) for more than 2 years [1] Direct damage and large indirect losses occurred to many medium-rise buildings, especially to pre-2004' precast concrete-framed buildings, as a result of small or moderate EQ ground motions in Christchurch CBD 2010 [1][2][3] and in Wellington CBD 2013 and 2016 [4][5][6].…”