Dear Frank,

Thank you for your request made under the Official Information Act, which we received on 9 June. You requested:

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Buildings and other structures (excl transmission towers) Could you please provide a list of all built infrastructure throughout nz (eg buildings, substations etc) required for the National grid or parts there of to remain functioning after a seismic event (as required of transpower as a lifeline utility under the civil defence act) with their current earthquake rating (%nbs) at IL4 or other similar assessment methodology as applicable to the structure typology.

I assume you do not own any dam structures

Transmission Towers
I assume there are typical typologies of transmission tower, to make it more straightforward to answer my request could you please provide me the different typologies of tower and their generic earthquake rating (%nbs) at IL4 or other similar assessment methodology as applicable to the structure typology for the seismic zones they are located within.
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We are processing your request and will respond to you as soon as we can, but in any event by 7 July 2023. If you have any questions in the meantime you can reply to this email.

Kind regards,
Vanessa

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Hi Frank

 

We refer to your request, which we have outlined below:

 

Buildings and other structures (excl transmission towers)
Could you please provide a list of all built infrastructure throughout nz
(eg buildings, substations etc) required for the National grid  or parts
there of to remain functioning after a seismic event (as required of
transpower as a lifeline utility under the civil defence act) with their
current earthquake rating (%nbs) at IL4 or other similar assessment
methodology as applicable to the structure typology.

 

I assume you do not own any dam structures

 

Transmission Towers

I assume there are typical typologies of transmission tower, to make it
more straightforward to answer my request could you please provide me the
different typologies of tower and their generic earthquake rating (%nbs)
at IL4 or other similar assessment methodology as applicable to the
structure typology for the seismic zones they are located within.

 

Please see our responses to each of your questions in turn below.

 

Buildings and other structures (excluding Transmission Towers)

 

Transpower has a Seismic Programme, which is in its third iteration. Each
iteration has followed the Engineering Assessment Guidelines outlined by
the Ministry of Business Innovation and Employment (MBIE) for identifying
earthquake prone buildings (EPB’s).

 

Transpower has identified 323 buildings and other structures (excluding
Transmission Towers) as IL4.  The 323 buildings and other structures are
comprised of the following types:

 

Type of building / structure Number of such
buildings/structures
Control Rooms 156
Switchgear/switchrooms 68
Warehouses 15
Other (including 84
buildings/huts/garages/structures)
Total 323

 

Previously, in each iteration, IL4 buildings were reviewed based on the
purpose, era and type of construction.  Seismic assessments were
prioritised accordingly. This resulted in 133 buildings being strengthened
to 75% NBS (IL4) or greater based on the standard in 2015.  The current
iteration of the Seismic Programme is reviewing buildings previously not
assessed or which require reassessment.

 

We have summarised our IL4 Buildings (and other structures, excluding
Transmission Towers) and their ratings groups (as at 15 June 2023) below. 
We have also attached a spreadsheet with each building’s rating (as at 15
June 2023).  In accordance with section 16 of the OIA we have identified
each building in the attached spreadsheet with an anonymised, unique
identifier. 

 

The data in this email, and attachment, is correct as at 15 June, but we
note as our Seismic Programme is active and ongoing new assessments and
reassessments continue to occur and the data will change accordingly.  We
note the NBS for IL4 is a higher standard than for IL2 and other
buildings.

 

Type of IL4 building / structure Number of such
buildings/structures
and %NBS for IL4 (as at assessment date)
Control Rooms Total: 156
Built 2015 onwards to current standards 12
NBS 75% or greater 94
NBS between 35% and 74% 13
NBS below 35% 18
Built before 2015 and awaiting assessment 19
   
Switchgear/switchrooms Total: 68
Built 2015 onwards to current standards 41
NBS 75% or greater 14
NBS between 35% and 74% 1
Built before 2015 and awaiting assessment 12
   
Warehouses Total: 15
NBS 75% or greater 5
NBS between 35% and 74% 1
NBS below 35% 2
Built before 2015 and awaiting assessment 7
   
Other (including Total: 84
buildings/huts/garages/structures)
Built 2015 onwards to current standards 5
NBS 75% or greater 35
NBS between 35% and 74% 8
NBS below 35% 11
Built before 2015 and awaiting assessment 25

 

As you will see, we have 58 buildings which were built in 2015 onwards to
the latest building code (including seismic requirements).  These
buildings will only require a seismic assessment when there is a IL4
seismic standard change. 

 

We have 63 buildings, which were constructed between 1978 and 2015 and
generally are constructed of materials and in a manner that our external
advisors deemed to be low-risk.  These buildings will be screened and
assessed in 2023 as part of the current iteration of the Seismic
Programme.  There are plans to strengthen any buildings, as required
following the 2023 screening and assessment, to 75% NBS (IL4) or greater
during our next funding period (known as a Regulatory Control Period or
RCP) (as part of our resilience programme), subject to the Commerce
Commission’s approval of our RCP4 proposal.  The order of strengthening
works being based on the building’s criticality and life-safety.

 

We risk assure the low-rated (less than 35% NBS) IL4 buildings and ensure
they are safe for human occupation, including by adopting, where
applicable, appropriate controls based on an our independent qualified
specialist engineering advisor’s assessment.  A NBS (for IL4 buildings)
rating of less than 35% indicates that elements of the building structure
will be damaged in a major earthquake, not that the building itself will
pose a life safety risk.

 

As an additional monitoring and assessment tool in near real-time, we have
a Seismic Triage Asset Reporting Tool (START) across all of our IL4
buildings.  It uses geonet data, seismic assessment and construction
information to assess, as soon as geonet information is available (usually
in less than 10 minutes) a building’s response in a seismic event and
enables Transpower to notify its workers as to whether it is safe to
enter/re-enter a building, or requires an engineering assessment prior to
entry.

 

We note we do not own any dams.  We do own water tanks, which are excluded
from this data.

 

Transmission Towers

Transpower does not calculate seismic ratings for its existing
transmission line towers. Experience from past earthquakes both in New
Zealand and internationally indicates transmission lines consistently have
excellent resilience against seismic events. This is primarily because the
design loads from extreme wind and snow / ice events typically exceed
those arising from seismic events. It is for this reason that the
Transpower policy excludes seismic design for transmission lines. This
applies to all tower types.  

 

Transpower does complete seismic design for new tower foundations where
there is location-based seismic risk, including liquefaction, lateral
spreading, slope stability, rock fall and fault movement. If these risks
apply to a location, the seismic loading will be determined using an
ultimate-limit event using the same return period as the weather-related
loading criteria. 

 

Regards

The Official Information Act Team

 

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