Southland Museum & Art Gallery Trust Board
19 March 2018
PO Box 1012
INVERCARGILL 9840
Attention: Mr P. Horner
Building Assets and Museum Manager
Dear Paul,
Southland Museum & Art Gallery: Review of November 2013 DEE Report
As requested in your E-mail dated 2 March 2018, following my walk-through
inspection of the Southland Museum & Art Gallery building at Gala Street,
Invercargill, on 1 March 2018, I have carried out a review of the Detailed
Engineering Evaluation – Quantitative Assessment Report prepared by Opus
International Consultants Ltd dated 29 November 2013. This Opus report
identified the various constructions that make up the Southland Museum & Art
Gallery building, and assessed the earthquake resistant capacity of the building
as a whole to be less than 34%NBS; hence ‘earthquake-prone’.
Relationship of DEE to Current Seismic Assessment Methodology for Buildings
Prior to the Canterbury Earthquake Sequence of 2010 – 11, the seismic resistant
structural capacity of existing buildings was assessed using the 2006 Guidelines1
published by the New Zealand Society for Earthquake Engineering, with
earthquake loadings derived from the New Zealand Standard NZS 1170: Part 52.
Immediately following the Canterbury Earthquakes engineers incorporated the
‘lessons learnt’ from the effects of the earthquake into supplementary documents
to assist in the assessment of existing building damaged by the earthquake
events and elsewhere in the country. A series of live documents3 were produced
by the Engineering Advisory Group to Government. These guideline documents
were referred to as the DEE Guidelines.
These DEE Guidelines tended to be specific to the issues identified in
Christchurch, Therefore, further development of the guidelines was carried out
under the administration and financial support of MBIE, with technical input
from the technical societies of Engineering New Zealand (previously the
Institution of Professional Engineers New Zealand). The resultant series of
publications
The Seismic Assessment of Existing Buildings (
the Guidelines) was
1 Assessment and Improvement of the Structural Performance of Buildings in Earthquakes:
Prioritisation, Initial Evaluation, Detailed Assessment, Improvement Measures
Recommendations of a NZSEE Study Group, June 2006.
2 NZS 1170.5: 2004: Structural Design Actions Part 5: Earthquake Actions – New Zealand
published by Standards New Zealand 2004
3 Engineering Advisory Group, Guidance on Detailed Engineering Evaluation of
Earthquake Affected Non-residential Buildings in Canterbury, Part 2 Evaluation
Procedure, Draft Prepared by the Engineering Advisory Group, Revision 7, May 2012.
and
Engineering Advisory Group, Guidance on Detailed Engineering Evaluation of Nonresidential
buildings, Part 3 Technical Guidance, Draft Prepared by the Engineering
Advisory Group, Rev 3, May 2012.
Southland Museum & Art Gallery Building: Review of Seismic Assessment
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W D C Clark 19 March 2018
published on 1 July 2017, to provides a technical basis for engineers to carry out
seismic assessments of existing buildings within New Zealand.
The Guidelines
support seismic assessments for a range of purposes, including whether or not a
building is earthquake-prone in terms of the Building Act 2004 [Building
(Earthquake-prone Buildings) Amendment Act 2016], and more generally for
property risk identification. The current building assessment guidelines are
available from http://www.eq-assess.org.nz/
with earthquake loadings continued to be derived from the New Zealand
Standard NZS 1170: Part 52.
DEE Assessment of the Southland Museum & Art Gallery Building:
Relevance to Current Requirement for Seismic Assessment of Buildings
I have reviewed the November 2013 DEE report prepared by Opus on the
Southland Museum & Art Gallery building, and the available construction
drawings that you provided for my review. The Opus report is comprehensive
and identifies the ‘Critical Structural Weakness’ in each of the four structures
that make up the museum & art gallery building. The methodology that Opus
used for the assessment of the elements of the building was appropriate, and
inline with developments taking place in 2013 that lead to the July 2017
Guidelines.
Further to the areas of structure covered by the Opus report, the consequential
effect of the 14 November 2016 Kaikoura Earthquake on precast concrete
flooring systems, has relevance for the Southland Museum & Art Gallery
Building. A number of multi-storey buildings in Wellington, where the precast
concrete flooring system was supported on a seismic resistant frame, sustained
damage to the flooring units at their supports. As the frames swayed under the
earthquake action, hinging occurred in the beams adjacent to the supporting
columns. After a number of cycles of yielding at the beam hinges, the hinge zone
grew in length with the potential for the flooring unit to come off their seating.
This loss of support caused three flooring units to collapse in one Wellington
building.
Considering the Southland Museum & Art Gallery building, there is the potential
for a similar flooring system failure mechanism to occur in the 1960 and 1988
additions where ‘Double TT’ precast concrete flooring units are used to form the
first and second floors. In addition, the ‘Shell Beams’ that form the main seismic
frames of the 1960 and 1988 additions may be vulnerable to extensive damage
at the hinge zones during a long duration seismic event. These potential areas of
structural failure reinforce the Opus assessment of the Museum & Art Gallery
building’s seismic resistance as being less than 33%NBS.
In my opinion, the conclusions of the Opus report provide a supportable
assessment that meets the criteria of the 2017 Guidelines for the seismic
assessment of existing buildings. Therefore, under the current Building Act 2004,
Building Amendment Act 2016 and Regulations, the Museum & Art Gallery
building is probably ‘earthquake-prone’. On the basis of seismic assessment
reporting submitted to the Invercargill City Council, they will determine if the
building is earthquake-prone.
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W D C Clark 19 March 2018
Consideration of Structural Strengthening or Replacement
In section 10 Remedial Options of the Opus report, a series of items for structural
strengthening are identified that must be addressed in the three main sections of
the Southland Museum & Art Gallery building to achieve a seismic resistant
capacity of 34%NBS or 67%NBS.
In my opinion, structural strengthening of the existing structures is unlikely to
achieve the level of protection required for the valuable material currently
contained in the building, or likely to be in the future. Any seismic resistant
performance will be compromised by the inherent difficulties of achieving a
consistent and reliable response from the various structures in any damaging
earthquake event. Whatever strengthening work is carried out there will remain
aspects of performance in the current four major structural elements that could
lead to significant damage. The resilient capacity of the structures to withstand an
earthquake that has an intensity of shaking greater than the design code seismic
loading will not be as great as that of a well-designed structure to current loading
and material code requirements. This aspect is very important to the survival of
the building, the level of damage sustained, and protection provided for the
building contents.
It is likely that the construction cost of such strengthening will only be marginally
less than lifting the roof frame off to allow demolition of the three original
structures and construction of a new structure to support the existing roof frame.
Any new structure will have greater functionality for the museum, art gallery and
service areas, and greater earthquake resistant capacity.
Conclusion
In my opinion, the Detailed Engineering Evaluation – Quantitative Assessment
Report prepared by Opus International Consultants Ltd dated 29 November
2013 remains relevant for the assessment of the Southland Museum & Art
Gallery building’s seismic resistant capacity. The report provides a fair and
supportable assessment, that essentially is aligned with the methodology setout
in
The Seismic Assessment of Existing Buildings guidelines
published by MBIE on 1
July 2017 to meet the requirements of the Building Act 2004, Building
(Earthquake-prone Buildings) Amendment Act 2016 and associated regulations.
It is confirmed that the Southland Museum & Art Gallery building is probably
‘earthquake-prone’.
I trust the review and conclusions outlined above assists you and the Trust
Board to move forward with your planning to upgrade the Southland Museum &
Art Gallery building. I would be pleased to answer any further queries you may
have that are raised by my review.
Yours Sincerely,
Win Clark
BE(Civil) FEngNZ CPEng IntPE(NZ)
92 Hill Road
Phone: +64 4 565 3650
Belmont
Mobile: +64 21 522 663
Lower Hutt 5010
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W D C Clark 19 March 2018
