31 July 2020
Waitomo District Council
Our ref:1250/7667//MDC Admin
Building DSA Letter.docx
PO Box 404
Te Kuiti 3941
Attention: Quin Powell
Dear Quin,
Detailed Seismic Reassessment of Waitomo District Council Administration Building
As advised, the building no longer requires post-disaster functions; as such, it is not required to meet
Importance Level 4 (IL4). We have now completed a review and update of the Detailed Seismic
Assessment (DSA) of the Waitomo District Council Administration building at Importance Level 2 (IL2).
The reassessment was carried out after reviewing all the provided documents noted below in the basis of
assessment.
Executive Summary
The two-storey part of the building attained the following percentage new building standard in the
two principal directions:
Two-Storey Structure
Transverse: 70%NBS (IL2).
Longitudinal: 75%NBS (IL2)
Hence the building is classed as low or medium risk.
The detailed seismic reassessment is considered to provide a relatively quick, high-level and qualitative
measure of the building’s performance.
Introduction
This detailed seismic reassessment has been based on the original DSA of two-storey structure only at
IL4. The critical structural weakness of two-storey structure is 40%
NBS (IL4) at the first level in
transverse direction.
Basis for the Reassessment
The information we have used for our DSA reassessment includes:
Previous IEP report done by DMC Ltd; received at 28/06/2019.
Partial building structural drawings as made available, received at 05/07/2019.
Geotechnical Assessment provided by Mark T Mitchell Ltd, which considers the site soil to be soil
class C. received at 28/06/2019.
Previous site inspection notes, no destructive testing.
Original DSA report for IL4 purpose by GHD Ltd. Issued to client at 26/08/2019.
Waitomo District Council Administration Building
Detailed Seismic Assessment Results
Our detailed seismic assessment of the two-storey part of building indicates the building can achieve
41
%NBS (IL4) in the longitudinal direction and 40
%NBS (IL4) in the transverse direction with soil class
C. After the removal of post-disaster function, the building becomes IL2 with a corresponding decrease in
earthquake return period and magnitude of load. The detailed seismic reassessment of this part of
building therefore indicates a seismic performance rating of 70
%NBS (IL2), corresponding to a ‘Grade B’
building as defined by the New Zealand Society for Earthquake Engineering (NZSEE) building grading
scheme. This is above the threshold for earthquake prone buildings (34
%NBS) and above the threshold
for earthquake risk buildings (67
%NBS) as recommended by the NZSEE.
Discussion
Our detailed seismic reassessment concluded that the Administration Building is 70%
NBS (IL2). This
seismic performance rating is considered accurate, as it is based up the detailed seismic assessment
result for IL4.
Conclusion
Our detailed seismic reassessment for this building, carried out using the previous DSA results indicates
overall scores of the buildings are as follows;
Two-Storey and overall Building – 70
%NBS (IL2) (corresponds to a Grade B building, as defined by
the NZSEE building grading scheme.)
We trust this letter of detailed seismic reassessment meets your current requirements. We would be
pleased to discuss further with you any issues raised in this report.
Please do not hesitate to contact me if you would like clarification of any aspect of this letter.
Yours sincerely
Edison Luo
Hannah Blythe
CPEng no. 1017182
Service Group Manager – Structures, Auckland
Senior Structural Engineer – Structures, Auckland
09 370 8129
09 370 829
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