Seismic response of instrumented structures

Sponsors: NZ Earthquake Commission (EQC), University of Canterbury (UC)

Collaborators: John Berrill, Hamish Avery (CSI), Kevin Faughtey, SR Uma (GNS Science)

Postgraduate researchers: Sam McHattie, Ethan Thomson

Quantative data from seismic arrays in structural and geotechnical systems offer one of the most informative means by which to understand case history observations and validate the accuracy of numerical seismic response models. To date we have examined the seismic response of several New Zealand structures in recent earthqaukes (as noted further below). We have also used instrumental responses of soil deposits to understand the limitations of general site response methodologies.

Seismic response of the UC Physics Building in the 2010-2011 Canterbury earthquakes (McHattie, 2013)

Recorded instrument data was examined and analysed to determine how the UC Physics Building performed during earthquake-induced ground motions. Ten of the largest earthquake events from the 2010-11 Canterbury earthquake sequence were selected in order to understand the seismic response under various levels of demand. Peak response amplitude values were found which characterise the demand from each event. Spectral analysis techniques were utilised to find the natural periods of the structure in each orthogonal direction. Significant torsional and rocking responses were also identified from the recorded ground motions. In addition, the observed building response is used to scrutinise the adequacy of NZ design code prescriptions for fundamental period, response spectra, floor acceleration and effective member stiffness. The efficacy of conventional numerical modelling assumptions for representing the UC Physics Building were also examined using the observed building response.

Seismic response of instrumented structures in the July/August 2011 Seddon/Lake Grassmere earthquakes (Thomson and Bradley, 2014)

We have investigated the dynamic response of five instrumented structures in the greater Wellington region during the July/August 2013 Seddon/Lake Grassmere earthquakes. Six events ranging from Mw 5.6 - 6.6 were considered in the analysis of five different structures: GNS Science at Avalon, BNZ Centre Port, Majestic Centre (shown above), Victoria University Te Puni Village Tower, and Wellington Hospital. This preliminary investigation firstly involved determination of the fundamental period of each structure in the principal horizontal directions, and comparison with the simplified method proposed in NZS1170.5:2004. Secondly, the peak floor level acceleration distributions over the height of the structures were analysed and compared with the design provisions in NZS1170.5:2004 and ASCE/SEI7:2010., The results illustrate that the simplified equation for fundamental period in NZS1170.5:2004 often underestimated the fundamental period and could result with unconservative design forces when using forced based design, and that both NZS1170.5:2004 and ASCE/SEI7:2010 provisions for floor acceleration contain significant deficiencies due to the omission of the dependence of peak floor acceleration variation with height on vibration period.

Relevant Publications:

1. McHattie S. Seismic response of the UC Physics building in the Canterbury earthquakes. Master of Engineering Thesis. August 2013. Christchurch, New Zealand. 234pp.
1. Thomson E, Bradley BA. Preliminary analysis of instrumented Wellington building responses in the July/August 2013 Seddon/Lake Grassmere earthquakes. New Zealand Society for Earthquake Engineering Conference. 21-23 March 2014. Auckland, New Zealand. Paper 76. 10pp.