25 August 2011
Quakes Royal Commission Hearings Start 17 October
The Canterbury Earthquakes Royal Commission will begin hearings on 17 October 2011 at St Teresa Church Hall on the corner of Riccarton Road and Puriri Street in Christchurch.
The Commission will hold hearings on the issue of seismicity. They are expected to take about a week. Other hearings will be held about other topics later in the year and in the New Year.
The Commission is not able to set out a full schedule of the hearings until it receives the results of a separate investigation being carried out by the Department of Building and Housing into the failure of the CTV, PGC, Hotel Grand Chancellor and Forsyth Barr buildings. In the meantime the Commission is continuing with its own investigation of the failure of those buildings and many other buildings in the CBD, including those in or near where lives were lost on 22 February 2011.
“Our terms of reference require us to take the results of that investigation into account and determine the sequence of our inquiry having regard to its availability. Until the results of the departmental investigation are publicly available the Commission can not schedule hearings dealing with those buildings,” says Chair Justice Mark Cooper.
“Because the hearings in relation to the inspection of buildings and the ‘stickering’ or ‘placarding’ of buildings should logically follow consideration of the reasons for the failure of these buildings, those hearings also cannot be scheduled at this stage.
“It is important that the departmental investigation is thorough as that will assist the work of the Commission.”
On the issue of seismicity, the Commission has published a report on its website prepared by GNS Science. It deals with the level of earthquake risk in Christchurch, the nature and severity of the Canterbury earthquakes and the implications for Christchurch and New Zealand’s national seismic hazard model.
Professor Ralph Archuleta of the University of California at Santa Barbara and Professor Norman Ambrahamson of University of California at Berkeley are carrying out separate peer reviews of the report to ensure that advice given to the Commission reflects international understandings and best practice.
The Commission has called for submissions and evidence on the GNS Science report to be provided to it (preferably in electronic form) by 30 September 2011.
The Commission has also published on its website a report by Professor Emeritus Athol Carr of the University of Canterbury about Inelastic Response Spectra. The report contains technical information for the use of structural engineers to help them explain why observed damage has occurred to buildings as a result of the earthquakes. It will also help in identifying what damage not immediately apparent, may have occurred.
In coming weeks the Commission plans to publish further reports dealing with some of the other subjects that will be considered in public hearings. These include the characteristics of land in the Christchurch CBD, new building construction methods and technologies, and the performance of unreinforced masonry buildings in the earthquakes.
About the GNS Science Report
The GNS Science report is called ‘The Canterbury Earthquake sequence and implications for Seismic Design Levels’.
GNS Science advise the report was largely compiled from existing information, especially short-term projects to inform the rebuild of Christchurch and associated scientific investigation that has been underway since last September. There was also a lot of pre-existing background material. However, it also contains material that is new to the general public.
- Comparisons between the four principal earthquakes, such as on pages 31 and 72
- The map plots (Figures 3.4, 3.7, 3.9, 3.14)
- Preliminary Alpine Fault rupture modelling. GNS notes more modelling work needs to be undertaken.
About the Professor Emeritus Athol Carr Report
The Professor Emeritus Athol Carr report is called ‘Inelastic Response Spectra for the Christchurch Earthquake Records’.
Professor Carr advises the report resulted from observations that one of the premises used by structural engineers, worldwide, did not appear to hold when analyses were carried of buildings using the Christchurch earthquake records.
All design standards (or codes) assume, that for building with a longer natural period of free-vibration (in NZS 1170.5; 2004 long is greater than 0.7 seconds, typically for buildings of four or five stories) that the displacements of the building define to behave in a ductile manner, the presumption for virtually all buildings built in New Zealand, the displacements would be the same (or similar) to those of a building which behaved elastically (no damage).
Ductile buildings with a short natural period would expect larger displacements than those for the linear elastic building. The observations from the spectra presented indicate that the displacements could be considerably larger for buildings with natural periods up three seconds (i.e. to about 18 stories).
This assumption by all design standards has had some criticism for several decades but this criticism has largely been ignored, as of minor consequence. However, it is a fundamental feature in the way the design forces (actions) and displacements are computed for design.
Professor Carr advises the continued use of this assumption needs real investigation. This could be particularly important for the new methods of structural design which start off with a displacement spectra which is obtained from the current acceleration design spectra using this equal displacement assumption.
Senior Communications Advisor
Canterbury Earthquakes Royal Commission
Phone +64 3 7413004 or +64 21 621 656