Sir Howard Morrison Performing Arts Centre

Report

Detailed Seismic Assessment – Sir Howard Morrison Performing Arts Centre

Prepared for Rotorua Lakes Council (Client)

Prepared by Beca Limited (Beca)

23 April 2018


Beca // 23 April 2018

5640377 // NZ1-14797867-23 0.23 // ii

Executive Summary

Background

Beca has been engaged to prepare a Detailed Seismic Assessment (DSA) report for Rotorua Lakes Council

(RLC), the owner of the Sir Howard Morrison Performing Arts Centre (SHMPAC) located at 1170 Fenton

Street, Rotorua, to describe the results of our quantitative assessment. This assessment follows a Seismic

Assessment Review for the building dated 28 April 2015 which included a high level independent structural

assessment of the seismic capacity of the building. Beca has also previously completed a Concept Seismic

Strengthening Report Targeting 67%NBS, dated 23 January 2017 based on the previous high level seismic

assessment.

Building Description

The Sir Howard Morrison Performing Arts Centre was constructed circa 1938 for the Rotorua Borough

Council. The building is comprised of multiple structures at different elevations, predominantly without any

seismic separations with the exception of the Boiler/Transformer Room, and Stairwell at the western end of

the Concert Hall. The different areas of the building are labelled in Figure 1.

Since construction, the building has undergone a number of extensions, alterations and refits including some

limited earthquake strengthening. However, a large portion of the structure remains unchanged.

The building is listed by Heritage New Zealand as a ‘Historic Place Category 1’ structure.



5640377 // NZ1-14797867-23 0.23 // iii

Figure 1: Locations of Structures that Make Up the Building

Assessed Seismic Rating

The results of our quantitative seismic assessment indicate the building’s earthquake rating is currently less

than 34%NBS (New Building Standard) assessed in accordance with the guideline document The Seismic

Assessment of Existing Buildings - Technical Guidelines for Engineering Assessments, dated July 2017.The

focus of the assessment using these guidelines is on the life safety of those occupying and those

immediately outside the building, rather than building damage and reparability considerations or business

interruption.

The earthquake rating is based on an Importance Level 3 (IL3) structure, with the exception of the external

stairwell adjacent to the Concert Hall, Transformer and Boiler House which are importance Level 2 (IL2)

structures. For all structures a design life of 50 years has been adopted, in accordance with the joint

Australian/New Zealand Standard – Structural Design Actions Part 0, AS/NZS 1170/0:2002, as being

deemed appropriate for this building.

This site subsoil class for this DSA has been based on class D for assessment of the primary structural

system and class C when considering parts loading in accordance with the New Zealand Design Standard –

Structural design actions Part 5: Earthquake actions, NZS 1170.5:2004. The reason for this is conflicting

results from previous geotechnical reporting of the site subsoil class. In terms of earthquake loading we have

adopted the more onerous soil class.



5640377 // NZ1-14797867-23 0.23 // iv

Our assessment concludes that the building is currently a Grade D building following the Engineering

Assessment Guidelines building grading scheme. Grade D buildings represent a life-safety risk to occupants

comparable to 10-25 times that expected for a new building, indicating a high risk exposure.

A building with an earthquake rating less than 34%NBS fulfils one of the requirements for the Territorial

Authority to consider it to be an Earthquake-Prone Building (EPB) in terms of the Building Act 2004. A

building rating less than 67%NBS is considered as an Earthquake Risk Building (ERB) by the New Zealand

Society for Earthquake Engineering. Since the Sir Howard Morrison Performing Arts Centre is currently less

than 34%NBS it is possible Rotorua Lakes Council may determine the buildings status as earthquake prone.

Our assessment identified the following structural weaknesses or items scoring <67%NBS, in the building:

Table 1: Summary of seismic scores for areas <67%NBS

System Direction %NBS Failure

type

Notes

Foyer Truss Transverse (N-S

direction)

25%NBS Ductile Buckling of the bottom chord. Sensitive to

soil-structure interaction effects and

interaction between the north and south

wings.

Supper

Room/Kitchenette

walls

Both directions

25%NBS Brittle Unreinforced concrete block wall out of plane, and a suspended unreinforced pumice concrete block wall with no reliable load path.

Storage Room Transverse (N-S)

directions

25%NBS Ductile

/Brittle

Reinforced concrete wall out-of-plane and

potential loss of gravity support to plant

support beams.

North Wing Frame Transverse (N-S)

directions

45%NBS Brittle Governed by the beam – column joint

detailing. Assuming no diaphragm or other

mitigating measures.

Northeast Wing

Frame

Transverse (N-S)

direction

50%NBS Brittle Our calculations determined that ‘failure’ of

the roof truss, could occur at <34%NBS,

resulting in redistributed and alternate load

paths/ mechanisms being activated to

maintain roof support. The steel roof truss

fixings in combination with a lack of robust

diaphragm or roof bracing system, appear

to be particularly deficient.

Concert Hall

Frame

Transverse (N-S)

direction

30%NBS Ductile Buckling of the props. This is the result of

changing from Soil Class C to Soil Class D,

after prop design, based on further

geotechnical data being made available.

North/South Wing

end walls

Longitudinal (E-W )

direction

30%NBS Brittle Unreinforced pumice concrete block wall.

Invasive investigations suggest the outer

whythes are unsupported out of plane.

Supper Room

Walls

Longitudinal (E-W)

and Transverse (N-

S) directions

45%NBS Brittle Unreinforced pumice concrete block walls

out of plane.



5640377 // NZ1-14797867-23 0.23 // v


type

Notes

North Wing Admin

Walls

Transverse (N-S)

directions


out of plane.

Currently the walls have a Polyplast layer

for out of plane strength, however we don’t

consider this provides any substantial

increase in capacity.

Auditorium Transverse (N-S)

directions

50%NBS Ductile Frame governed by ultimate drift limits, due

to loss of frame action from roof truss end

diagonal member buckling.

Fly Tower Both directions 25%NBS Brittle Deficient Reid brace connectors at ends of

cross bracing, typical.

Transverse 32%NBS Brittle Potential for loss of gravity support to truss

over proscenium arch.

Dressing Room Both directions 45%NBS Brittle The diaphragm capacity is limited by the

collector and tie capacities.

Function Room Both directions >90%NBS Ductile Our calculations determined that the roof

beams were the critical elements in the

frame and could resist levels of earthquake

shaking to at least 90% ULS (IL3).

The low %NBS is compounded by the fact that some of the failures are characterised as ‘brittle’, as noted in

the table above. A brittle failure mode is essentially an instantaneous failure with little or no warning.

Essentially load builds up in an element before snapping and, once this happens, the element has no further

capacity to distribute load.

A ‘ductile’ failure is a more favourable failure as the section can undergo some deformations and maintain

vertical support without collapse. Essentially the member/connection will bend and stretch without snapping.

As such, the building can dissipate or absorb seismic forces by deforming and still support the weight of the

building and resist some lateral load. Generally, ductile systems, although potentially significantly damaged

post-earthquake pose a reduced life-safety risk.

There have been significant advances in seismic loading and design principles since this building was initially

designed. It is therefore expected that the older structures of this building are not up to current building

standards and the findings of this report are consistent with the buildings age.

Previous Assessment

The previous high level Seismic Assessment was undertaken in accordance with the New Zealand Society

for Earthquake Engineering (NZSEE) guidelines for Assessment and improvement of the Structural



5640377 // NZ1-14797867-23 0.23 // vi

Performance of Buildings in earthquakes1. The high level assessment focussed on the higher risk older

structures that were constructed between the 1930s and 1971 as follows;

� Concert Hall. � Supper Room. � North-West Wing. � North-East Wing. � Auditorium.

This Detailed Seismic Assessment considers all structures that make up SHMPAC including the more

modern sections of the building that were not considered in the previous assessment.

Next Steps We recommend you consider carrying out the following steps:

� Review the seismic strengthening schemes and associated cost estimate in the separate cost report.

� Consult with the Heritage Architect in relation to the strengthening proposed.

� Coordinate any other upgrade works proposed to the building.

� Undertake detailed design of the strengthening schemes

1 NOTE: The New Zealand Society for Earthquake Engineering (NZSEE) guidelines for Assessment and

improvement of the Structural Performance of Buildings in earthquakes was replaced by The Seismic

Assessment of Existing Buildings - Technical Guidelines for Engineering Assessments, for seismic

assessments in New Zealand in July 2017.



5640377 // NZ1-14797867-23 0.23 // i

Contents

1 Introduction ........................................................................................................ 3

Scope of Assessment ...................................................................................................................... 3

Previous Assessment ...................................................................................................................... 3

Regulatory Environment and Design Standards ............................................................................. 4

Assessment Methodology................................................................................................................ 5

Explanatory Statement .................................................................................................................... 5

2 Building Description .......................................................................................... 7

General ............................................................................................................................................ 7

Heritage status ................................................................................................................................. 8

Geotechnical Considerations ........................................................................................................... 9

Building Design .............................................................................................................................. 12

Structural Systems ......................................................................................................................... 13

3 Results of Seismic Assessment .................................................................... 16

Primary Seismic System Limiting Mechanisms ............................................................................. 18

Staircase and Safe Egress ............................................................................................................ 27

4 Commentary on Associated Seismic Risks .................................................. 30

Risks from Adjacent Buildings ....................................................................................................... 30

Risks from Non-structural Building Elements ................................................................................ 30

5 Assessment of Seismic Risk .......................................................................... 30

Seismic Risk and Performance Levels .......................................................................................... 30

6 Next Steps ........................................................................................................ 32

Appendices

Appendix A

Sources of Information

Appendix B

Concrete Test Report

Appendix C

Basis of Seismic Assessment

Appendix D

Building Inspection Photographs

Appendix E

Structural Drawings



5640377 // NZ1-14797867-23 0.23 // ii



5640377 // NZ1-14797867-23 0.23 // 3

1 Introduction

Beca Ltd (Beca) has been engaged by Rotorua Lakes Council (RLC) to undertake a detailed seismic

assessment of the Sir Howard Morrison Performing Arts Centre (SHMPAC) located at 1170 Fenton Street,

Rotorua. This report describes the results of our quantitative seismic assessment. It follows on from the Seismic

Assessment Review Report dated 28 April 2015 and the Concept Seismic Strengthening Targeting 67%NBS

Report dated 23 January 2017.

Scope of Assessment

The purpose of this assessment is to establish the seismic risk and vulnerability of the Sir Howard Morrison

Performing Arts Centre. The assessment has been completed in accordance with the guidance documents The

Seismic Assessment of Existing Buildings – Technical Guidelines for Engineering Assessments, dated July

2017 (Engineering Assessment Guidelines) with the focus of life-safety of those occupying and those

immediately outside the building, rather than building damage and reparability considerations or business

interruption.

Our scope of work includes:

� A review of our previous high level Seismic Assessment and Concept Seismic Strengthening Targeting

67%NBS (IL3) reports.

� Review of the Council property files, structural drawings, geotechnical reports, intrusive and non-intrusive

on-site investigation findings, and photos from site.

� The assembly of an analytical model of the building structure based on the information gained by a review of

the drawings along with our site investigation and knowledge of the detailing used for structures of this era.

� An evaluation of the capacity of the key structural elements of the building and the seismic demands

(internal forces and ductility) on these elements, as derived from our analytical models.

� A brief commentary on the seismic hierarchy and attributes of key building features such as stairs, exterior

cladding, and the associated seismic risk.

� Preparation of concept level options for structural strengthening with order of magnitude costs.

� A summary of the findings and comments on any differences with the previous Seismic Assessment Review

and Concept Seismic Strengthening reports, and general recommendations about further actions.

Previous Assessment

Beca has previously completed an independent high level structural assessment of the seismic capacity of the

building which is summarised in our report dated 28 April 2015. The building was assessed on the basis of it

being an Importance Level 3 (IL3) structure, and a site subsoil class C, under the NZSEE Assessment and

Improvement of the Structural performance of Buildings in Earthquakes guidelines (current at the time of the

high level structural assessment)2. The high level assessment determined that the building has a rating of 35%

of the New Building Standard (%NBS) which corresponds to a Grade C building, indicating moderate risk as

defined by the NZSEE building grading scheme.

The high level structural assessment of the seismic capacity of the building provided a useful indication of the

building’s seismic rating in an earthquake, however the scope was limited to what was considered the higher

risk older structures constructed between the 1930s and 1971, Specifically;

� Concert Hall. � Supper Room.

2 NOTE: As of July 2017 the NZSEE Seismic Assessment guidelines were replaced by The Seismic

Assessment of Existing Buildings - Technical Guidelines for Engineering Assessments, dated July 2017.



5640377 // NZ1-14797867-23 0.23 // 4

� North-West Wing. � North-East Wing. � Auditorium.

In this DSA the results from the previous assessment have been revised using a more comprehensive seismic

assessment, in accordance with the Engineering Assessment Guidelines. We have developed a 3D model of

the building in ETABS to aid us in assessing the interaction between different structures within the building. This

DSA assesses all areas of the building including the more modern structures which were not assessed

previously.

Regulatory Environment and Design Standards

The Earthquake-Prone Building regulatory framework underwent significant changes during 2016 and 2017 as

a result of learnings from the Christchurch earthquakes, and more recently, the 2016 Kaikoura earthquake. This

resulted in the Building (Earthquake-prone Buildings) Amendment Act 2016, the Building (Specified Systems,

Change the Use, and Earthquake-prone Buildings) Regulations 2017 including the Earthquake-prone Building

Methodology, and the technical guideline document The Seismic Assessment of Existing Buildings - Technical

Guidelines for Engineering Assessments. The important aspects of this regulatory framework are summarised

below.

Earthquake-Prone Buildings (EPBs) are defined in Section 133AB of the Building (Earthquake-prone Buildings)

Amendment Act 2016 as buildings whose ultimate capacity will be exceeded in a moderate earthquake and, if it

were to collapse, would likely result in injury or death or damage to another property. A moderate earthquake is

defined as approximately one-third as strong but of the same duration as the earthquake shaking assumed in

the design of a new building.

The official determination of whether or not a building is Earthquake-Prone is the responsibility of the relevant

Territorial Authority (TA). The earthquake rating resulting from an engineering assessment is only one, albeit

significant, aspect considered by the TA in making their determination. If the TA determines a building to be

Earthquake-prone, it will issue an EPB notice for the building and include it on the EPB register. The Building

(Earthquake-prone Buildings) Amendment Act 2016 then defines timeframes within which the owner must carry

out building work (i.e. upgrade or demolish) to ensure the building is no longer Earthquake-prone. These

timeframes range from 7.5 years to 35 years depending on the building type (priority or normal) and location

(high, medium or low risk areas).

The Building (Specified Systems, Change the Use, and Earthquake-prone Buildings) Regulations 2017 made

significant changes to the system for identifying and remediating Earthquake-prone buildings. These include:

� providing an operational basis for identifying earthquake-prone buildings – the EPB Methodology

� new definitions for key terms including ‘Earthquake-prone Buildings’ and ‘ultimate capacity’

� a requirement to categorise Earthquake-prone Buildings in terms of their earthquake rating

� providing a national-based system in place of individual earthquake-prone building policies for each TA

The Technical Guidelines document used by engineers to carry out seismic assessments is an integral part of

the EPB Methodology.

In addition, the New Zealand Society for Earthquake Engineering (NZSEE) define a building with a seismic

rating less than 67%NBS as an Earthquake-Risk Building (ERB), and recommend a minimum target

strengthening level of 67%NBS.

It is considered impractical and unaffordable to design every building to withstand the largest earthquake

imaginable. Consequently, with respect to the determination of design loads for natural hazards, the New

Zealand Loading Standard adopts a probabilistic approach that takes into account the exposure hazard at a

given location, along with factors such as building importance.



5640377 // NZ1-14797867-23 0.23 // 5

Thus, the Loading Standard may be said to adopt a risk management approach in setting the loading levels that

a given building is required to withstand.

For Importance Level 3 (IL3) buildings (e.g. structures that may contain people in crowds), the “design”

earthquake load is set at the 1 in 1000 year return period earthquake event. This event has approximately a 5%

probability of exceedance over the assumed 50 year life of a building.

Assessment Methodology

We have adopted a stepped analysis approach to undertaking the seismic assessment of the Sir Howard

Morrison building starting with simpler analysis methods and progressively employing more sophisticated

methods of analysis and calculations to determine the seismic rating of the building. The techniques used are

generally as outlined in the guideline document The Seismic Assessment of Existing Buildings - Technical

Guidelines for Engineering Assessments, dated July 2017 (the Engineering Assessment Guidelines). Previous

versions of this guideline document were referred to as the NZSEE Guidelines, as they were produced by the

New Zealand Society for Earthquake Engineering. The guidelines have now been fully revised, with the new

version produced by three technical engineering societies (NZSEE, the Structural Engineering Society

(SESOC) and NZ Geotechnical Society (NZGS)), in conjunction with the Ministry of Business, Innovation and

Employment (MBIE) and the Earthquake Commission (EQC).

Our methodology is briefly summarised below, which generally follows the key steps of the Simple Lateral

Mechanism Analysis (SLaMA) technique described in Chapter 2 and Appendix 2A of the Engineering

Assessment Guidelines:

� Review of the available structural drawings to identify the main structural elements and any apparent

“structural weaknesses” of the building.

� Visual inspection of the building including the general presence and arrangement of the structures and

additions, the concrete frames, shear walls, stairs and relationship to adjacent buildings, carried out between

the 22nd June and 19th September 2017 by Beca structural engineers, including identification of non-

structural elements that may present a significant life-safety hazard.

� Selection of appropriate member properties and determination of structural element probable capacities.

� Calculation of the expected seismic actions on the building following the current New Zealand loading

standards (NZS1170).

� Hand analysis of selected key elements of the building to determine the likely failure mechanisms of these

subassemblies, and the whole building.

� Development of an elastic three-dimensional (3D) ETABS computer model of the building for analysis of the

force distributions.

� Development of elastic two-dimensional (2D) computer models for the analysis of key structural elements.

� Undertake a qualitative assessment of potential geo-hazards e.g. liquefaction, lateral spreading, slope

instability and their consequence of the performance of the structural system.

� Determination of the likely seismic rating of the building compared with an equivalent new building at the site

based on our inspections, the structural weaknesses identified, our calculations, and our engineering

judgment.

Explanatory Statement

� This report has been prepared by Beca at the request of our Client and is exclusively for our Client’s use for

the purpose for which it is intended in accordance with the agreed scope of work. Beca accepts no

responsibility or liability to any third party for any loss or damage whatsoever arising out of the use of or

reliance on this report by that party or any party other than our Client.

� The inspections of the building discussed in this report have been undertaken to assist in the structural

assessment of the building structure for seismic loads only. This assessment does not consider gravity or

wind loading or cover building services or fire safety systems, or the building finishes, glazing system or the

weather tightness envelope.



5640377 // NZ1-14797867-23 0.23 // 6

� This assessment does not include an assessment of the building condition or repairs that may be required.

� No geotechnical ground investigations, subsurface or slope stability assessments have been undertaken.

Geotechnical input to the assessment has been based on a desktop review of readily available information

about the site and general area.

� Beca is not able to give any warranty or guarantee that all possible damage, defects, conditions or qualities

have been identified. The work done by Beca and the advice given is therefore on a reasonable endeavours

basis.

� Except to the extent that Beca expressly indicates in the report, no assessment has been made to determine

whether or not the building complies with the building codes or other relevant codes, standards, guidelines,

legislation, plans, etc.

� The assessment is based on the information available to Beca at the time of the assessment and assumes

the construction drawings supplied are an accurate record of the building. Further information may affect the

results and conclusion of this assessment. The information used to undertake the seismic assessment is

listed in Appendix A.

� Beca has not considered any environmental matters and accepts no liability, whether in contract, tort, or

otherwise for any environmental issues.

� The basis of Beca’s advice and our responsibility to our Client is set out above and in the terms of

engagement with our Client.



5640377 // NZ1-14797867-23 0.23 // 7

2 Building Description

General

Summary information about the building is presented in the following table. Reference Information used to

undertake this seismic assessment is listed in Appendix A.

Table 2: Building summary information

Item Details Comment

Building name Sir Howard Morrison Performing Arts Centre (SHMPAC)

Street Address 1170 Fenton Street, Rotorua

Age 79 years, Original structure constructed in 1938

There have been multiple additions to the original building since 1938, however most of the original building remains.

No condition assessment has been undertaken in this DSA

Description / Building Occupancy SHMPAC includes an Auditorium, Fly Tower, Concert Hall, Dressing areas, office space, Storage areas, Function Room, Supper Room, Kitchen, Foyer and Plant Room.

Importance Level 3 (except IL2 for the stair adjacent to the Concert Hall, Transformer and Boiler House)

More than 300 people can congregate in one area.

Site sub soil class Primarily structure: D

Parts: C

Note: The previous high-level assessment was based on a site sub-soil class C. Since the high-level assessment, further geotechnical data has been made available, suggesting site sub-soil class D. Consequently we have adopted the more onerous soil class.

Building Footprint / Floor Area Approximately 3400m2

No. of storeys / basements Typically one and two storey building, with a three storey Fly Tower.

Structural system Refer to Section 2.5. Structural systems differ for different structures that make up the building.

Earthquake resisting system Predominantly concrete frame or shear walls, with the exception of the fly tower which is a steel braced lattice structure. Refer to Section 2.5.

Earthquake resisting systems differ for different structures that make up the building.

Foundation system Typically, shallow concrete pads and ground beams

Stair system Precast, in-situ concrete, and steel

Other notable features Canopy at the front of the building on western side, and canopy on the south western side.

Past seismic strengthening Strengthening including addition of shotcrete to some pumice concrete walls and strengthening of some connections.

Minimal strengthening to connections and shotcrete on walls undertaken in 1993

Temporary props installed June 2017



5640377 // NZ1-14797867-23 0.23 // 8

Item Details Comment

Temporary props installed to support concrete columns in the Concert Hall.

Construction information Structural drawings Drawings provided by Rotorua Lakes Council, including the original Rotorua Borough Council drawings, Sigma, and Works.

Likely Design Standards NZSS95:1935, NZSS1900:1965, NZS4203:1976, NZS3101: 1982, NZS4203:1984, NZS4203 1992: NZS4203: 1994, NZS1170:2004

Heritage Status Historic Place Category 1.

Other

Figure 2: Plan of the building showing construction date of different sections

Photographs of the building are included in Appendix D.

Heritage status

The building is listed by the Heritage New Zealand as a ‘Historic Place Category 1’.



5640377 // NZ1-14797867-23 0.23 // 9

Geotechnical Considerations

2.3.1 Historical Information

Our desktop assessment has considered the following sources of information:

� Published Geological Map of the Rotorua area (GNS, 2010)

� Terrane (2009) and Works Consultancy (1993) reports on the SHMPAC

� Works Consultancy (1993) report on the neighbouring Civic Buildings

� Coffey (2015) report on the neighbouring Rotorua Tourism Centre and our Beca (2015) peer review of the

same

� Terrane (2014) geotechnical IEP assessment for the Rotorua Tourism Centre

� BSK (2006) detailed seismic assessment for the Rotorua Public Library

� Opus (2006, 2012) reports on the neighbouring Rotorua Police Station

� Bay of Plenty Regional Council (BoPRC) groundwater and geothermal bore data.

2.3.2 Summary of Historical Advice

Two geotechnical reports have been provided which detail assessments for alterations of the SHMPAC in

relation to the original 1930s and 1970s parts of the building. The key points from these reports are

summarised below.

� Works Consultancy (1993)

– The site is located within the Rotorua Caldera and underlain by alluvium of Holocene age consisting of

pumiceous sands and fine gravels with beds of soft to firm clay.

– The consolidation of soft clay layers may induce settlements of up to 90mm for pad and strip foundations.

� Terrane (2009)

– Site investigations measured groundwater at 3.5m below ground level (bgl).

– A peak seismic ground acceleration of 0.415g was adopted in the design which was noted to correspond

to a 1/1000 APE for an Importance Level 3 (IL3) building.

– The recommended site subsoil category for seismic design actions was taken as Class C based on NZS

1170.5:2004.

– Under the design criteria adopted in the assessment, liquefaction was not considered to be an issue for

structures at this site.

– The consolidation of soft clay layers may induce settlements of up to 30mm for pad foundations.

We note the available data suggests some variability in the ground conditions is likely across the building

footprint.

2.3.3 Current View of Liquefaction Potential

The current state of knowledge with regards to understanding liquefaction potential at the site and surrounding

area has advanced since the Terrane (2009) report. Liquefaction potential and the conditions that may trigger

liquefaction are now better understood and the recommendations provided in the original Terrane (2009) report

are no longer considered current.

We have undertaken a quantitative liquefaction assessment for this site utilising data from Coffey (2015) for the

nearby Rotorua Library and the NZGS/MBIE Guidelines for Earthquake Geotechnical Engineering Practice

(2016).



5640377 // NZ1-14797867-23 0.23 // 10

2.3.4 Geohazards at the Site

Potential geohazards that we have identified that could affect the site are summarised in Table 3 below.

Table 3: Potential Geohazards

Potential Geohazard Hazard Comment

Liquefaction High risk Liquefaction can have a number of effects that require consideration for this DSA. These effects may include:

� Settlement/differential settlement,

� Cyclic ground movements,

� Increased cyclic deflections of foundations

� Lateral spread, and

� Reduction in bearing capacity

Collapse of Hydrothermally Altered Soil/Rock

High risk The failure of hydrothermally altered materials due to seismic shaking can have similar effects on a site as that of liquefaction. These effects may include:

� Settlement/differential settlement,

� Reduction in bearing capacity

Fault Rupture Very low risk No known active faults in the vicinity of the site

Slope Instability N/A

The site is located on an area of open and relatively flat ground

Rockfall N/A No rock-fall sources nearby

Landslide Dam-Break Flood N/A No dams located upstream

Dam Break N/A No dams located upstream

Tsunami N/A The site is not located near a coastline

The principal geohazards at this site are liquefaction and collapse of hydrothermally altered materials;

specifically, the differential settlement associated with these hazards. Settlement effects as a result of

liquefaction can be either free field (affecting the general area,) or can be in specific response to the static or

cyclic loads applied by the structure. The collapse of hydrothermally altered soils will likely result in subsidence.

Other Geohazards noted in Table 3 are unlikely to occur at this site.

2.3.5 2017 Geotechnical Detailed Seismic Assessment

2.3.5.1 Current Focus

The focus of a DSA is the potential for a step change in the structural system, giving rise to a life safety risk.

Serviceability concerns are not the main focus of a DSA, however recommendations for further work to address

potential damage limitation or serviceability concerns are discussed in Section 2.3.6.

2.3.5.2 Current Site Soil Class

SHMPAC is located within an area of lake deposits and lies within the Government Gardens area of geothermal

activity. The soils in the area are likely to be hydrothermally altered and therefore weakened by geothermal

weathering.

Geotechnical site investigations obtained from the historical information extend at most to 35m depth and do

not encounter rock. Groundwater bores within the area, which are not reliable for geological descriptions,

suggest that rock may lie at 50-60m bgl. This information suggests that a site subsoil Class of C (shallow soil

site) is highly unlikely. For this DSA we recommend classifying the site as Class D (deep soil site). Although an

intermediate classification between Class C and Class D is possible, further research and physical

investigations in regards to the depth to rock and the shear wave velocities of the overlying soils are required to



5640377 // NZ1-14797867-23 0.23 // 11

determine the site class with certainty in accordance with the requirements set out in NZS1170.5:2004

incorporating Amendment 1.

2.3.5.3 Liquefaction Potential

The Ultimate Limit State (ULS) earthquake, for an Importance level (IL) 3 building, with a 50 year design

working life has an Annual Probability of Exceedance (APE) of 1/1000. This corresponds to a Peak Ground

Acceleration (PGA) of 0.39g for soil class D with a representative magnitude of 6.0 (determined from NZTA

Bridge Manual 3rd ed in accordance with NZGS Module 1) (NZTA, 2016).

We have undertaken a liquefaction assessment using the existing Coffey (2015) Cone Penetration Test (CPT)

data, noting that the available data is located around the neighbouring Rotorua Tourism Centre. Our

assessment indicates that the ground may experience localised liquefaction/softening in an event exceeding

1/175 APE (0.17g or 43% of ULS) with widespread liquefaction anticipated in events with an APE of greater

than 1/250 APE (0.20g or 51% of ULS).

We therefore recommend that the DSA assume liquefaction will initiate at shaking levels of approximately 50%

of ULS (IL3).

Based on the reported performance of low rise, shallow founded buildings supported on level ground subject to

liquefaction, the following consequence of liquefaction could be anticipated:

� Differential settlement of heavily loaded foundations and lightly loaded floors/aprons etc.

� Differential settlement associated with variations in the ground conditions across the site.

� Differential settlement between the concert wing and meeting room wing.

� Buoyancy effects on light, deeply embedded elements (e.g. the orchestra pit).

� Significant ‘softening’ of foundation response leading to rocking and ratcheting (vertically and rotationally) of

heavily loaded foundations.

Based on observations from Christchurch, the above effects may lead to differential settlements of several

hundreds of millimetres between foundation elements that are not well tied together.

The system performance of the Performing Arts Centre is currently assumed to be structurally dominated in

accordance with Part C4 of the Guideline for the seismic assessment of buildings (NZSEE, 2017).

2.3.5.4 Hydrothermally Altered Soil and Rock

SHMPAC is located within the Government Gardens area of geothermal activity. The soils in the area are likely

to be hydrothermally altered and therefore weakened by geothermal weathering. The historical information we

have reviewed suggests that the level of hydrothermal alteration begins at approximately 2m bgl.

Geothermal systems are developed by the transportation of water, at times acidic, down through the underlying

soils which is then heated by geologic processes (e.g. deep magma) before rising back toward the surface. As

the water moves, it dissolves minerals resulting in a porous and weakened structure. This fragile microfabric

may collapse or crumble under seismic shaking, which could result in subsidence beneath the foundations of

the building.

The sensitivity of hydrothermally altered soils to levels of seismic shaking is not known and could occur either

before or after liquefaction. The level of subsidence likely to result from such a collapse is unknown.

2.3.6 Recommendations for Future Assessments

We recommend additional testing be undertaken around the building to supplement any future assessment, and

to assist with the confirmation of site class (if required).



5640377 // NZ1-14797867-23 0.23 // 12

Building Design

The first unified national loading and building design standard, NZSS95:1935 Model Building By-Law, was

introduced following the catastrophic 1931 Napier earthquake. This code required the building to be designed

for a nominal lateral force applied uniformly up the building. A revision to the loading and building design

standard was made in 1955, introducing minor improvements to reinforced concrete design.

There were significant changes to the knowledge base of structural engineers in the mid-1960s and the 1970s.

The NZS1900:1965 loading standard considered variations in regional seismicity and effects of dynamic

response in the calculation of seismic coefficients. Ductility requirements were introduced in NZS1900:1965,

but without clear guidance on how to achieve the ductility capacity.

Much research and development occurred in the late 1960s and early 1970s. Research and development in

New Zealand in the 1970s set the early benchmark for the design and detailing of ductile reinforced concrete

structures to resist earthquake loading. These findings were incorporated into a new loadings code

NZS4203:1976 and a new concrete code NZS 3101:1982.

A ductile structure designed to modern codes is expected to be able to undergo relatively large displacements

without collapse. Ductile structures are also able to dissipate energy and resist repeated cycles of seismic loads

without excessive strength degradation. Buildings designed with these features provide a higher level of life

safety performance in severe earthquakes compared with other buildings without these features.

The current New Zealand standard for derivation of Earthquake Loads is NZS1170.5:2004 Structural Design

Actions Part 5: Earthquake actions – New Zealand. It, along with materials standards as mentioned above, is

significantly advanced from that which the original 1935 standard which SHMPAC was likely designed to. It is

therefore reasonable to expect that the older structures of the building are going to be deficient when assessed

against current building standards, in terms of basic strength, available ductility, resilience, basic code-

compliance etc.



5640377 // NZ1-14797867-23 0.23 // 13

Structural Systems

Descriptions of the gravity structure as well as the primary lateral load resisting systems for each structure that

form the Sir Howard Morrison Performing Arts Centre are identified below;

Table 4: Structural systems that form SHMPAC

Structure Gravity Structure Lateral Resisting System

Concert Hall � Timber-framed roof supported by

reinforced concrete columns framing onto

pad foundations.

� Heavy reinforced pumice concrete infill

walls spanning between columns.

� North-south direction is reinforced concrete

framing comprising of cantilever columns

and tie beam and pad foundations to most

but not all grids.

� Three of the north-south frames are integral

with the Auditorium structural framing.

� East-west direction reinforced concrete

framing and infill.

� Reinforced pumice concrete infill between

concrete frames on all wall lines except the

west elevation which has shotcrete

strengthened pumice concrete block infill

walls.

� Timber roof comprising of laminated roof

beams, timber purlins and ‘straight’ sarking

(perpendicular to north and south walls).

� Laminated roof beams bolted to the main

auditorium columns, ‘fishtailed’ anchor bolts

to the reinforced concrete columns

elsewhere.

Supper Room � Open plan single storey structure

� Timber framed roof which is supported on

concrete columns and pumice concrete

cavity block infill.

� Internal timber-framed, plasterboard lined

partitions/walls.

� Concrete walls around internal kitchen

area

� Reinforced concrete framing and infill

pumice concrete blocks north-south. All

north-south frames are integral with the main

auditorium structural framing.

� Reinforced concrete framing and infill

pumice concrete blocks east-west (south

elevation)


beams, timber purlins and ‘straight’ sarking.

� Laminated roof beams bolted to the main

auditorium columns, ‘fishtailed’ anchor bolts

to the southern reinforced concrete columns.

� East and south elevations have pumice

concrete cavity block infill walls

� North (Auditorium) and west (Concert Hall)

elevations have reinforced pumice concrete

infill walls.

� The west and south elevations have

reinforced pumice concrete infill walls.



5640377 // NZ1-14797867-23 0.23 // 14


North-West Wing � Two-storey structure designed as part of

the original building.

� Timber-framed roof installed over the

original in 1950 additions.

� Roof supported on concrete frame.

� Some heavy walls including reinforced

concrete and pumice concrete cavity

block.

� First level reinforced concrete floor

continuous with North-East Wing.

� In-situ reinforced concrete stair.

� Reinforced concrete shear walls in both

directions. Longitudinally on grids B and D,

and transversely on grids 11 and 18.

� Reinforced concrete columns and beams

framing in both directions

� Cavity block infill with shotcrete overlay

strengthening on the east and west walls

and polyplast strengthening on the north and

south walls.

� Cast in-situ reinforced concrete first floor

diaphragm.


beams, timber purlins and ‘straight’ sarking.

� Laminated roof beams have limited capacity

‘fishtailed’ anchor bolts to the reinforced

concrete columns.

� The two eastern most grids (grid 11 and 13)

are integral with the main auditorium

structural framing. Concrete moment frame

and shear walls in north-south Direction on

both levels.

North-East Wing � Originally a single-storey structure with a

second storey added in 1950 alterations.

The single level structure is continuous

with the North-West Wing.

� Light-weight roof with steel trusses and

timber frame added in 1993 over original

roof structure.

� Concrete frames at both upper and lower

levels.

� First level reinforced concrete floor

continuous with North-West Wing

� Pumice concrete block walls between

concrete frames.

� Shear wall dominant in both directions.

In the longitudinal direction the North-

East Wing is tied into the Auditorium

and Plant Room/Kitchen shear walls,

and transversely is tied into the Plant

Room/Kitchen shear walls.

� Reinforced concrete column and beam

framing in both directions at ground level.

� Reinforced concrete column and beam

framing in both directions at first floor level,

however the upper level was an addition in

the 1950’s and appears to be pinned to the

lower frame.

� Cast in-situ reinforced concrete first floor

diaphragm.

� All north-south grid framing is integral with

the main auditorium structural framing.

� The original roof does not have sarking or

bracing but the 1993 addition has a plywood

diaphragm.

� Steel truss connections comprise of bolted

and welded fixings to the auditorium steel

columns and cast-in anchor bolts to the

northern first floor columns.

� Upper storey framing has reinforced

concrete infill to north and east elevations.

� There is no continuously sarked diaphragm

at the same level as the North-West Wing.



5640377 // NZ1-14797867-23 0.23 // 15


Auditorium � Lightweight roof with bolted steel roof

trusses.

� Heavy ceiling with a mass of cables

particularly at the eastern end of the

Auditorium, and lighting hangers.

� Concrete encased steel columns and

beams.

� Reinforced concrete wall infill to north

and south elevations.

� Concrete in-situ mezzanine and projector

room floor slabs with concrete encased

steel beams.

� North-south direction has steel (concrete

encased) columns and a roof truss creating

a frame.

� East-west direction has steel encased

columns and beams with reinforced concrete

infill providing shear wall behaviour.

� The roof has ‘straight’ sarking to achieve

diaphragm action, but is not continuous over

the length of the auditorium.

Fly Tower � Three storey structure designed as an

extension to the original auditorium.

� Lightweight steel and timber roof

� Concrete wall on the east elevation

� Foundations comprise of concrete ground

beams below main framing in both

directions.

� North –south direction has reinforced

concrete shear wall on the east side and a

braced portal frame on the west elevation.

� East-west direction has steel tension only

cross bracing (Reid) up the full height.

� On the east elevation the fly tower is integral

with the back of house dressing room.

� The fly tower is predominantly a steel braced

lattice structure.

East Dressing

Room

� Two storey structure designed as an

extension to the original Auditorium

� Concrete wall on the west elevation

� Floors at first and second level are

precast concrete units with cast in-situ

topping.

� Foundations comprise of concrete ground

beams below main framing in both

directions.

� North –south direction has a reinforced

concrete shear wall on the west elevation.

� East-west direction has reinforced concrete

moment frames, and shear walls located

either side of central stair.

� Reinforced concrete floor diaphragms on the

first and second level of the dressing room.

� The east dressing room is integral with the

fly tower on the west elevation.

Storage Room � Heavy reinforced concrete walls in both

directions

� Light weight roof with timber rafters.

� The mezzanine level is support by a steel

gravity structure connected into the

reinforced concrete shear walls.

� Heavy reinforced concrete shear walls in

both directions

Foyer � Light weight roof with steel trusses

supported on concrete columns

� Concrete columns provide support in both

directions as cantilevers fixed at the base in

one direction and moment frame in the other

direction (footing follows curve of arc).

Kitchen/Plant Room � Heavy reinforced concrete shear walls in

both directions

� Heavy reinforced concrete shear walls in

both directions



5640377 // NZ1-14797867-23 0.23 // 16


Function Room � Light weight roof with steel trusses

supported on concrete columns

� Concrete columns provide support in both

directions as cantilevers fixed at the base in

one direction and moment frame in the other

direction (footing follows curve of arc).

South-West Stair � Reinforced concrete (RC) stairs

supported on RC walls on the east and

west elevations on shallow foundations

and columns

� North-south direction has reinforced

concrete shear walls.

� East-west direction relies on frame action

provided by RC columns and beams,

coupled with the stair flights.

Transformer / Boiler

House

� Light-weight timber-framed roof

supported on reinforced masonry block

walls on shallow foundations.

� Both directions have reinforced masonry

block shear walls.

3 Results of Seismic Assessment

The results of our quantitative seismic assessment indicate the building’s earthquake rating to be less than

34%NBS (at IL3).

Table 5 presents the evaluated seismic performance in terms of %NBS of each individual structure in each

loading direction.

Table 5: Summary of seismic score for areas <67%NBS (IL3)


type

Notes

Foyer Truss Transverse (N-S

direction)

25%NBS Ductile Buckling of the bottom chord. Sensitive to

soil-structure interaction effects and

interaction between the north and south

wings.

Supper

Room/Kitchenette

walls

Both directions

25%NBS Brittle Unreinforced concrete block wall out of plane, and a suspended unreinforced pumice concrete block wall with no reliable load path.

Storage Room Transverse (N-S)

directions

25%NBS Ductile

/Brittle

Reinforced concrete wall out-of-plane and

potential loss of gravity support to plant

support beams.

North Wing Frame Transverse (N-S)

directions

45%NBS Brittle Governed by the beam – column joint

detailing. Assuming no diaphragm or other

mitigating measures.



5640377 // NZ1-14797867-23 0.23 // 17


type

Notes

Northeast Wing

Frame

Transverse (N-S)

direction

50%NBS Brittle Our calculations determined that ‘failure’ of

the roof truss, could occur at <34%NBS,

resulting in redistributed and alternate load

paths/ mechanisms being activated to

maintain roof support. The steel roof truss

fixings in combination with a lack of robust

diaphragm or roof bracing system, appear

to be particularly deficient.

Concert Hall

Frame

Transverse (N-S)

direction

30%NBS Ductile Buckling of the props. This is the result of

changing from Soil Class C to Soil Class D,

after prop design, based on further

geotechnical data being made available.

North/South Wing

end walls

Longitudinal (E-W )

direction

30%NBS Brittle Unreinforced pumice concrete block wall.

Invasive investigations suggest the outer

whythes are unsupported out of plane.

Supper Room

Walls

Longitudinal (E-W)

and Transverse (N-

S) directions


out of plane.

North Wing Admin

Walls

Transverse (N-S)

directions


out of plane.

Currently the walls have a Polyplast layer

for out of plane strength, however we don’t

consider this provides any substantial

increase in capacity.

Auditorium Transverse (N-S)

directions

50%NBS Ductile Frame governed by ultimate drift limits, due

to loss of frame action from roof trussed

diagonal member buckling.

Fly Tower Both directions 25%NBS Brittle Deficient Reid brace connectors at ends of

cross bracing, typical.

Transverse 32%NBS Brittle Potential for loss of gravity support to truss

over the proscenium arch.

Dressing Room Both directions 45%NBS Brittle The diaphragm capacity is limited by the

collector and tie capacities.

Function Room Both directions >90%NBS Ductile Our calculations determined that the roof

beams were the critical elements in the

frame and could resist levels of earthquake

shaking to at least 90% ULS (IL3).



5640377 // NZ1-14797867-23 0.23 // 18

Primary Seismic System Limiting Mechanisms

The seismic rating of the Sir Howard Morrison Performing Arts Centre (SHMPAC) is limited by:

3.1.1 Foyer

The most limiting mechanism for this area of SHMPAC is identified as the foyer trusses on grids 14 and 15,

refer Figure 3 below. In particular, buckling of the bottom chord, potentially resulting in the collapse of the foyer

roof. We assessed these elements as approximately 25%NBS.

Another limiting mechanism for this area is the connection of the foyer truss to the north and south wings.

Under earthquake shaking at 67%NBS liquefaction is likely and large differential displacements between the

north and south wings may occur. As a result the bolted fixings between the trusses and walls/columns could

potentially pull out resulting in the foyer truss becoming unstable with no dependable lateral or vertical load

system.

Figure 3: Foyer trusses spanning between north and south wings

3.1.2 Supper/Kitchen walls

A limiting element in the Supper Room is the unreinforced pumice concrete block walls between the Supper

Room and the Kitchen and a suspended unreinforced pumice concrete block wall above the Kitchen. There is

currently significant cracking at the ends of these walls, suggesting only limited strength and unreliable load

paths. Under moderate shaking the suspended wall may lose vertical support, and the Supper Room/Kitchen

wall become unstable/collapse out of plane. These elements are only expected to be a localised life-safety risk

and not result in catastrophic collapse of the building. Refer to Figure 4 below for the location of these walls. We

assessed these elements as approximately 25%NBS.



5640377 // NZ1-14797867-23 0.23 // 19

Figure 4: Location of critical Supper Room/Kitchen walls

3.1.3 Storage Room

A limiting element in the Storage room is the reinforced concrete walls on gridline L (south elevation). This wall

spans 13.4m horizontally with minimal support at roof level. Due to the lack of support and large span, the wall

is subject to large displacements. There is also a mezzanine structure supported by the storage room wall. The

mezzanine gravity structure is connected to the wall with 2-M12 bolts (embedment unknown) and can be

expected to only sustain minor deflections prior to failure. In addition to the risk of the wall falling out, there is a

significant risk the mezzanine structure supporting HVAC plant will lose gravity support. Refer to Figure 5 and

Figure 6 below for the location of this wall. We assessed the Storage room wall as approximately 25%NBS.

Figure 5: Storage Room wall - critical out of plane



5640377 // NZ1-14797867-23 0.23 // 20

Figure 6: Mezzanine gravity support structure in the Storage Room

3.1.4 North Wing Frame – Grids 11 to 18

Based on our intrusive investigation findings for the similar Concert Hall structure, we have assumed there is no

dependable roof diaphragm connection to the North Wing walls. The limiting mechanism for the North Wing,

between grids 11 and 18 is the shear capacity of the beam-column joints in the transverse frame at first floor

level on grid 13. The deficiency of the beam-column joint means the frame cannot yield, and is potentially

subject to brittle failure. Under moderate shaking the transverse frame may be susceptible to significant shear

damage/failure in the joint area, potentially resulting in loss of gravity load bearing capacity in the column. Refer

to Figure 7 for an elevation of a transverse frame in the North Wing. We assessed the North wing frame on grid

13 as approximately 45%NBS. This is a lower bound based on the known deficiencies of this particular beam-

column joint.



5640377 // NZ1-14797867-23 0.23 // 21

Figure 7: North wing transverse frame

3.1.5 North East Wing – Grids 7 - 11

The limiting mechanism for the North Wing, between grids 11 and 18 is the shear capacity of the bolts

connecting the top chord of the truss to the Gird B frame.

In the 1950’s an additional level was added to this area of the North Wing. Based on the available drawings

there is limited reinforcing that continues from the level. As a result the additional 1950’s frame is considered to

be pinned at the first floor level on the north elevation. On the south elevation, all framing is integral with the

Auditorium structural framing.

The performance of the North East Wing appears to be governed by the steel roof structure, including fixings

and northern wall out-of-plane capacity. Our calculations determined that the ‘failure’ of the fixings to the bottom

chord and roof components could occur at <34%NBS, resulting in redistribution and alternate load

paths/mechanisms being activated to maintain roof support. The steel truss roof fixings in combination with a

lack of a robust roof diaphragm or roof bracing system, appear to be particularly deficient.

Refer to Figure 8 and Figure 9 below for a typical elevation of these frames. We assessed the North-East Wing

frames between grids 7 and 11, based on the wall out-of-plane capacity following the failure of the above

elements as approximately 50%NBS.



5640377 // NZ1-14797867-23 0.23 // 22

Figure 8: Elevation of the North Wing transverse frame

Figure 9: Indication of the trusses between grids 7 and 11 in the North Wing

3.1.6 Concert Hall

The significant limiting mechanism for the South Wing, between grids 11 and 18 is the buckling of the props in

the transverse frame. The props are a recent strengthening addition to the Concert Hall and were installed in

June 2017. Based on the geotechnical information at the time of this strengthening, the props were designed for

site subsoil class C. Additional geotechnical data obtained post June 2017 indicates the site sub soil class to be

D. The consequence of this soil class change results in an increase in earthquake loading of approximately

30%. Refer to Figure 10 below for location of props.



5640377 // NZ1-14797867-23 0.23 // 23

Prior to the props being installed, the Concert Hall system was an upside down portal frame with the critical

element being the beam-column joint detailing.

During the invasive inspections we identified there was no connection between the roof diaphragm and the

north, south, and east walls. We have assumed based on this that the west wall also has no dependable

connection. As a result, our calculations are based on there being no roof diaphragm.

We assessed the South wing frames between grids 11 and 18 as approximately 25%NBS.

Figure 10: Location of props in the Concert Hall

3.1.7 North and South Wing end walls on grid 18

The limiting mechanism for the North and South Wing end walls, on grid 18, is the out of plane capacity of the

unreinforced pumice concrete blocks. Previously these end walls have been strengthened with 200mm of

reinforced concrete shotcrete. However, during the site inspections, it was noted that the dowel between the

shotcrete and pumice block was only embedded in the inner whythe of the block, leaving the outer whythe

susceptible to falling under earthquake shaking. We assessed the North and South wing pumice concrete

block infill walls on grid 18 as approximately 30%NBS.



5640377 // NZ1-14797867-23 0.23 // 24

Figure 11: Concert Hall end wall on grid 18. North Wing end wall similar

3.1.8 Supper Room Walls – Grid H-K and Grid 7-11

The limiting mechanism for the South Wing (external Supper Room walls), between grids 7-11 (south elevation)

and grids H-K (east elevation) is the out of plane capacity of the infill unreinforced pumice concrete cavity

blocks. Under earthquake shaking there is potential for the infill pumice concrete cavity blocks to fall out

creating a localised life-safety hazard. Refer to Figure 12 for the location of these walls. We assessed the

Supper Room walls between grids 7-11 and H-K as approximately 45%NBS.

Figure 12: Unreinforced infill pumice block walls around the Supper Room

3.1.9 North-West Wing Infill Walls – Grid 11-18

The limiting mechanism for the North Wing walls, between grids 11-18 is the out of plane capacity of the infill

pumice concrete cavity blocks on the first floor. Refer to Figure 13 below for an indication of the extent of cavity

blocks on the first floor in the North Wing. Under earthquake shaking there is potential for the infill pumice



5640377 // NZ1-14797867-23 0.23 // 25

concrete cavity blocks to fall out creating a localised life safety hazard. We assessed the North Wing walls

between grids 11-18 as approximately 55%NBS.

Figure 13: Extent of cavity block wall on the first floor of the North Wing

3.1.10 Auditorium frames

Based on our intrusive investigation findings for the Concert Hall structure, we have assumed there is no

dependable roof diaphragm connection to the Auditorium walls. The limiting mechanism for the Auditorium

frames in the transverse direction is the hold down bolts at the base connection and roof level drift. During the

invasive investigations we identified the roof diaphragm is not continuous along the full length of the Auditorium.

Currently there is a large cut in the diaphragm at the western end that is approximately 400mm wide x 8000mm

long.

Our calculations determined that the failure of the truss diagonal could occur at relatively low levels of shaking

(<34%NBS), resulting in redistribution and alternative load paths/mechanisms being activated to maintain

structural integrity. The frames with the transverse seating beams are considered to be more resilient than

those at the eastern end of the Auditorium which only comprise of columns and roof beams (plus foundation tie

beams).Refer to Figure 14 for a typical elevation of the Auditorium truss. We assessed the Auditorium frames

as approximately 50%NBS.

Based on our intrusive investigation findings for the similar Concert Hall structure, we have assumed there is no

dependable diaphragm connection to the Auditorium walls.h

Figure 14: Auditorium truss



5640377 // NZ1-14797867-23 0.23 // 26

3.1.11 Fly Tower

The limiting mechanism for the Fly Tower is the deficiency of the Reid brace (banana) end connectors. Recently

(Sept 2015) it has become clear, based on current available test data, that the Reid brace system is likely to fail

in a brittle manner, at the connector. Available design calculations for the Fly Tower, provided by RLC, indicate

that the system was designed considering, nominal ductility (µ=1.25), subsoil class C and importance level 2.

Our assessment checks are based on elastic loads (µ=1.0), sub-soil class D, and importance level 3. This

substantially increases the seismic demands.

Our calculations determined that a failure of the Reid brace system could occur at relatively low levels of

shaking (25%NBS), potentially resulting in the collapse of the Fly Tower, and loss of lateral stability of the back

of house dressing room. In addition, the truss above the proscenium arch (truss 4, refer to Figure 15, Truss “4”)

appears to be designed to support gravity loads only. We have considered the support of this truss as a result

of the lateral loading induced by displacement of the fly tower. It is possible that the vertical columns denoted ‘F’

at approximate third points may act to support the truss should the end connections fail. However, the original

drawings do not provide these connection details and these were not viewed on site to confirm this. Without

confirmation of this, our assessment assumes that failure of the end connections may result in collapse of the

truss. On this basis, the fly tower truss has a score of 32%NBS based on the shear capacity of the truss end

connections. Although note, this is not the critical element.

Refer to Figure 15 for west elevation of the Fly Tower. We assessed the Fly Tower as approximately 25%NBS.

Figure 15: West elevation of the Fly Tower

3.1.12 Dressing Room / Back of House

The limiting mechanism for the Dressing Room is the first and second floor diaphragms. The diaphragms

comprise of precast floor units with in-situ topping reinforced with brittle non-ductile mesh. Under earthquake

shaking there is potential for premature diaphragm damage due to the brittle mesh reinforcement. We

assessed the Dressing Room / Back-of-House as approximately 45%NBS.



5640377 // NZ1-14797867-23 0.23 // 27

Figure 16 below is an indication of the location of the elements/areas that obtain a %NBS score less than

34%NBS and less than 67%NBS

Figure 16: Overall indication of the areas that score below 34%NBS and 67%NBS

Staircase and Safe Egress

The Department of Building and Housing issued Practice Advisory 13 in response to concerns about stair

collapse and damage observed in the Christchurch earthquake. The primary concern of this Practice Advisory

is staircases with sliding support details in mid to high-rise multi-storey buildings.

There are six main stair cases in the building, as shown in Figure 17. There are no known sliding support

details for these stairs. The Fly Tower stair cases are of steel-framed construction with steel grating treads. All

other are reinforced concrete construction adjacent to, or supported by shear walls. Our assessment of each of

the main stairs is summarised in Table 6 below.



5640377 // NZ1-14797867-23 0.23 // 28

Figure 17 Floor plan of SHMPAC showing main stair locations

Table 6 Stair assessment summary

Ref # Stair Locations Original Drawing Description and Assessment

1 Main Foyer

A reinforced concrete (RC) stair tied to floor slabs at the top and bottom. Provides main access and egress to and from the Auditorium.

Supported on RC shear walls which provide both gravity and lateral support.

The lateral stair support system has displacement compatibility with the primary supporting structures and therefore considered not to pose a significant life-safety hazard.

2 Dressing Room

A RC stair tied to floor slabs at the top and bottom. Provides main access and egress between the stage and dressing room floors.

Supported on RC beams at each end, and located adjacent to RC shear walls.

Located next to a shear wall, so differential displacements between landings will be limited. Therefore the stair is considered not to pose a significant life-safety hazard.



5640377 // NZ1-14797867-23 0.23 // 29

Ref # Stair Locations Original Drawing Description and Assessment

3 Fly Tower - South

A steel stair connected to concrete floor slabs and steel-framed landings. Provides service access between the stage and Fly Tower upper levels.

A relatively flexible stair system, supported on steel framing at one end, and used for service access only. Therefore the stair is considered not to pose a significant life-safety hazard.

4 Fly tower - North

As for stair # 3.

5 Auditorium Egress

A RC stair tied to a floor slab at the top and ground at the base. Provides main egress from the Auditorium, and access to the plant room.

Supported on an RC beam at the top, an RC wall at mid-landing, and ground beam on-grade and the base. Located adjacent to a RC shear wall.

Located next to a shear wall and not restrained at the base or mid-landing. Therefore the stair is considered not to pose a significant life-safety hazard.

6 North Wing - Admin

A RC stair tied to floor slabs at the top and bottom. Provides egress from the Admin area to outside.

Supported on RC beams at each end, and located adjacent to RC shear walls.

Located next to a shear wall, so differential displacements between landings will be limited. Therefore the stair is considered not to pose a significant life-safety hazard.

7 South Concert Hall

A disused RC stair structure separated from the Concert Hall. Tied to RC slab landings and walls at the end of each flight.

Considered not to pose a significant life-safety hazard.


5640377 // NZ1-14797867-23 0.23 // 30

4 Commentary on Associated Seismic Risks

Risks from Adjacent Buildings

SHMPAC is located in Rotorua’s CBD. Recent experience in Christchurch indicates that even if a building

performs well in a significant earthquake the impact of other adjacent and relatively close buildings may

affect whether it can be used in the immediate post-earthquake environment. SHMPAC is a standalone

building with the only building in close proximity being the Rotorua Lakes Council office building. In an

earthquake this may pose a risk to SHMPAC’ seismic vulnerability and accessibility.

Risks from Non-structural Building Elements

From our recent experience in evaluating similar buildings in Christchurch, non-structural building elements

(façade glass, ceilings, internal walls, overhead services) constitute a significant portion of the repair /

reinstatement cost following an earthquake. In a moderate seismic event, non-structural element damage

will likely contribute heavily to downtime and the repair costs.

For a new building, full-height partitions (glazed or Gib-board lining), glazed street facades and ceilings are

normally designed to accommodate the building’s deformations.

Concerns at SHMPAC in a significant seismic event include;

� The potential for the ceiling tiles in many of the different sections of the building to fall out of ceiling

frames.

� The potential for the large glass panels in the Foyer and the Function Room to be damaged.

� The potential for the heavy ceiling in the Auditorium to fall down.

We have not investigated the available deformation capacity of these elements as it is beyond the scope of

this report.

5 Assessment of Seismic Risk

Seismic Risk and Performance Levels

Our quantitative seismic assessment of the Sir Howard Morrison Performing Arts Centre indicates an

earthquake rating of less than 34%NBS (at IL3). The building has been assessed in accordance with the

guideline document The Assessment of existing Buildings – Technical Guidelines for Engineering

Assessments , dated July 2017 (Engineering Assessment Guidelines). The assessment result is based on

an Importance Level 3 (IL3) building, in accordance with the joint Australian/New Zealand Standard –

Structural Design Actions Part 0, AS/NZS 1170.0:2002 as being deemed appropriate for this building.

Therefore, the building is a Grade D building, following the Engineering Assessment Guidelines building

grading scheme. Grade D buildings represent a life-safety risk to occupants comparable to 10-25 times that

expected for a new building, indicating a high risk exposure.

The New Building Standard requires an IL3 building to have a low probability of collapse in a 1 in 1000-year

“design level” earthquake (i.e. an earthquake with a probability of exceedance of approximately 5% over the

assumed 50 year design life of a building).


5640377 // NZ1-14797867-23 0.23 // 31

Relative Earthquake Risk

Building Grade Percentage of New Building

Strength (%NBS)

Approx. Risk Relative to a New

Building

Risk Description

A+ >100 <1 low risk

A 80 to 100 1 to 2 times low risk

B 67 to 80 2 to 5 times low to medium risk

C 33 to 67 5 to 10 times medium risk

D 20 to 33 10 to 25 times high risk

E <20 more than 25 times very high risk

A building with an earthquake rating less than 34%NBS fulfils one of the requirements for the Territorial

Authority to consider it to be an Earthquake-Prone Building (EPB) in terms of the Building Act 2004. A

building rating less than 67%NBS is considered as an Earthquake Risk Building (ERB) by the New Zealand

Society for Earthquake Engineering.

Since SHMPAC is currently less than 34%NBS, Rotorua Lakes Council may determine the buildings status

as earthquake prone. If it does so, RLC will also issue an EPB notice for the building and include it on the

EQB register.


5640377 // NZ1-14797867-23 0.23 // 32

6 Next Steps

Since the seismic rating is less than 34%NBS, further action is required to meet the regulatory minimum

requirements set out in the Building (Earthquake-prone Buildings) Amendment Act 2016. We recommend

Rotorua Lakes Council consider carrying out the following next steps:

� Review the concept seismic strengthening schemes and associated cost estimate provided in a separate

cost report.

� Consult with their Heritage Architect in relation to the concept strengthening schemes proposed.

Coordinate any other upgrade works proposed to the building.

� Undertake detailed design of the strengthening scheme and documentation for Building Consent


5640377 // NZ1-14797867-19 0.19 // 33

Appendix A

Sources of Information


5640377 // NZ1-14797867-19 0.19 // 34

Sources of Information The following information was used to undertake the seismic assessment:

� Documents obtained from Rotorua Lakes Council comprising of scanned original structural drawings and

design calculations from different stages of construction, some original construction photographs, and

some geotechnical reports for SHMPAC and the surrounding area.

� Beca’s Seismic Assessment Review Report dated 28 April 2015 and Concept Seismic Strengthening

Targeting 67%NBS Report dated 23 January 2017.

� External and internal visual inspections of the building carried out by Beca between the 22nd June 2017

and 19th September 2017.

� Intrusive investigation findings such as concrete strengths, extent of diaphragms and presence of

reinforcing steel in concrete elements.

The following documents and references were available to undertake the seismic assessment:

� New Zealand Standard NZS1170 “Structural Design Actions”.

� New Zealand Standard NZS3101:2006 “Concrete Structures Standard”.

� New Zealand Standard NZS3404:1997 “Steel Structures Standard”.

� The Seismic Assessment of Existing Buildings - Technical Guidelines for Engineering Assessments,

dated July 2017.


5640377 // NZ1-14797867-19 0.19 // 35

Appendix B

Concrete Test Report

PAGE 1 OF 7 www.opus.co.nz

Opus International Consultants Ltd

P +64 4 587 0600

Opus Research

33 The Esplanade, Petone

PO Box 30 845, Lower Hutt 5040

New Zealand

25 October 2017

Craig Lavin

Beca Infrastructure Ltd

P O Box 903

Tauranga 3140

Ref: 524A17.00

Sir Howard Morrison Performing Arts Centre – Concrete Core Strength Results

Dear Craig

1. Introduction The seismic performance of the Sir Howard Morrison Performing Arts Centre (SHMPAC) in Rotorua is

currently being assessed and as part of that assessment the strength of the concrete was required to be

measured. Cores for concrete strength determination were delivered to Opus Research on 12 October

then tested on 24 October 2017. This letter reports the results of that testing.

2. Samples Twenty four nominally 84mm diameter concrete cores were removed from a variety of locations in the

SHMPAC building. A general description of the cores delivered is presented in Table 1. Representative

photos of each core type are presented in Figures 1 to 8.

Four cores were assessed to be unsuitable for compressive strength testing:

C1 (iii) – reinforcing bar cavity through the middle of the core.

C2 (ii) – core length less than diameter.

S1 (iii) – plastic conduit across core diameter.

S3 (iii) - core length less than diameter.

Twenty cores were subsequently tested for compressive strength.


Table 1: General Description of Cores

Core Identifier Concrete Description

C1

(i, ii, iii)

Concrete contains crushed volcanic aggregate with a maximum size of about

20mm but generally about 12mm. Concrete well compacted but appears

porous.

C2

(i, ii, iii)

Concrete contains rounded greywacke aggregate with a maximum size of

about 20mm. Concrete is well compacted.

S1

(i, ii, iii)

Concrete contains rounded greywacke aggregate with a maximum size of

about 20mm. Concrete is well compacted.

S2

(i, ii, iii)


20mm but generally about 12mm.

S3

(i, ii, iii)


20mm but generally about 12mm.

W1

(i, ii, iii)

Concrete contains crushed pumice aggregate with a maximum size of about

15mm but generally about 10mm. Concrete is well compacted.

W2

(i, ii, iii)


25mm. Concrete is well compacted.

W3

(i, ii, iii)

Concrete contains crushed pumice aggregate with a maximum size of about

15mm but generally about 10mm. Concrete is well compacted.

3. Methodology The core ends were first trimmed with a wet cut diamond saw.

The compressive strength of the concrete core samples was measured in accordance with Section 9

Determination of Strength in Compression of Drilled Cores from NZS 3112: Part 2 Tests Relating to the

Determination of Strength of Concrete. The cores were tested in the ‘dry’ state, i.e. stored in air at room

temperature for 7 days before testing at the completion of all preparation activities. This procedure was

chosen to represent the moisture condition of the concrete in the building.

The preferred length to diameter ratio for concrete core testing is 2:1 but this cannot always be achieved.

To account for this, when necessary the compressive strength was normalised to this aspect ratio using

the correction factors given in ASTM C 42 Standard Test Method for Obtaining and Testing Drilled Cores

and Sawed Beams of Concrete. The minimum length to diameter ratio allowed under this method is 1:1.

The core diameter preferred by NZS 3112 is 100mm for concrete containing aggregate with a nominal

maximum size of 19mm but in no case shall the diameter be less than four times the maximum aggregate

size. The maximum coarse aggregate size in these cores is generally less than 20mm so the 84mm core

diameter used meets this aggregate size requirement. For one set of cores, W2 (i, ii & iii), the maximum

coarse aggregate size is about 25mm so does not strictly meet this core diameter requirement.

4. Results The concrete core results are presented in Table 1.

The core failure mechanisms were all acceptable.

Table 2: Concrete Core Compressive Strength Results


Core Identifier Compressive Strength

(MPa)

Comments

C1 (i) 8.0 Weak porous concrete lacking in aggregate

C1 (ii) 15.5

C2 (i) 20.0

C2 (iii) 24.5

S1 (i) 40.0

S1 (ii) 37.0

S2 (i) 18.5

S2 (ii) 20.0 Nominally 16mm diameter round bar across core diameter. No

apparent impact on strength result.

S2 (iii) 24.5

S3 (i) 22.0

S3 (ii) 21.5

W1 (i) 7.0

W1 (ii) 8.5

W1 (iii) 8.5

W2 (i) 37.5

W2 (ii) 34.0

W2 (iii) 34.0 Nominally 10mm diameter round bar across core diameter. No

apparent impact on strength result.

W3 (i) 6.0

W3 (ii) 7.0

W3 (iii) 9.0

Prepared by:

Sheldon Bruce

Manager Asset Performance


Figure 1: Core C1 (ii).

Figure 2: Core C2 (iii).


Figure 3: Core S1 (ii).

Figure 4: Core S2 (i).


Figure 5: Core S3 (ii).

Figure 1: Core W1 (i).


Figure 1: Core W2 (iii).

Figure 1: Core W3 (i).


5640377 // NZ1-14797867-19 0.19 // 37

Appendix C

Basis of Seismic Assessment


5640377 // NZ1-14797867-19 0.19 // 38

Basis of Seismic Assessment C.1 Seismic Loading

The seismic design actions have been determined in accordance with NZS1170.5:2004 with the following

assumptions:

� Importance Level 3 structure (buildings that as a whole may contain people in crowds) and a Design Life

of 50 years.

� Site Location – Rotorua

� Subsoil class category D for the main structure and Subsoil class C for parts loading (due to conflicting

results from previous geotechnical reporting of the site subsoil class we have adopted the more onerous

soil class).

Only the Ultimate Limit State (ULS) loading are considered in the seismic assessment, which is concerned

with life safety of the occupants and collapse prevention.

C.2 Dead and Live Loads

The following basis has been used in establishing the seismic mass for the structure:

� Reinforced concrete for floor slabs, columns, beams and walls is normal weight with a density including

reinforcing of 2400 kg/m3, and in instances where the walls are pumice concrete a density including

reinforcing of 1800kg/m3.

� Structural steel is a normal weight steel with a density of 7600 kg/m3.

C.3 Assessment Assumptions

The key assumptions made during our assessment were as follows:

Item Assumption Comments

Steel grades fy= 228 MPa

fy= 255 MPa

fy=275 MPa

fy=300 MPa

fy=500 MPa

All reinforcing bar, used in the original 1930’s construction of SHMPAC.

All reinforcing bar, used in the 1950’s alteration works.

All reinforcing bar, used in the 1970’s alteration works.

Bar grade called up on the relevant drawings in the 1990’s alteration works.

Bar grade called up on the relevant drawings in the 1990’s alteration works.


5640377 // NZ1-14797867-19 0.19 // 39

Item Assumption Comments

Concrete strength

(Note: Concrete core strength tests were undertaken as part of the intrusive investigations. This assessment incorporates these results where applicable).

f’c=7MPa

f’c=20MPa

f’c=25MPa

f’c=35MPa

Pumice concrete used in the original 1930’s construction of SHMPAC.

Reinforced concrete used in the original 1930’s construction of SHMPAC.

Reinforced concrete used in the 1950’s alterations.

Reinforced concrete used in the 1970’s and 1990’s alterations.

Element Capacity Assessments Using probable material strengths and a hand analysis

This was carried out following the recommendations of the Engineering Assessment Guidelines.

Structural Analysis 3D Elastic Model in ETABS

2D Models in Space Gass of lateral resisting systems

ETABS models used to analyse force distribution between the various structures.

Period and demand of the building under seismic loading explored

Diaphragms Timber sarking roof diaphragms

Reinforced concrete floor diaphragms

Loads distributed based on tributary width.

Accidental Eccentricity Included in the assessment of the global system. Not considered important in the assessment of the areas with the flexible roof diaphragm.

Modelling Centreline beam and column modelling used

No rigid offsets used. This is conservative for drift.

The achievable seismic rating of the various structural elements has been estimated using the approach

described in the Engineering Assessment Guidelines.

C.4 Seismic Mass

The seismic mass has been computed adopting the NZS1170.5:2004 loading combination W = G + ΨE Qu =

G + 0.3Qu, for floor loading and G, with Ψ=0 for roofs not used for floor activities. No area reduction factor

was used to calculate the ultimate live load Qu, as a conservative assumption.

The seismic mass was determined for each of the areas and distributed equally to nodes in the computer

model


5640377 // NZ1-14797867-19 0.19 // 40

C.5 Seismic Coefficient

For the analysis of load distribution using ETABS, a building period of 0.4 seconds was assumed in each

direction. For particular elements that were considered using 2D space gass models with flexible diaphragms

the period was determined using the simplified Rayleigh method. In most instances the period of these

individual frames was approximately 1 second.


5640377 // NZ1-14797867-19 0.19 // 41

Appendix D

Building Inspection Photographs

Photo 1: Main foyer looking east towards the mezzanine and western end of the Auditorium

Photo 2: Main Foyer roof space looking south along the truss that spans between the north andsouth wings on grids 14 and 15. The truss chord members are indicated on the left of the truss spanimage.

Photo 3: Concert Hall end wall (grid 18) looking west. This end wall has previously beenstrengthened with 200mm shotcrete.

Photo 4: Timber sarking roof diaphragm at the eastern end of the Concert Hall. There isapproximately a 10mm20mm gap between the diaphragm and wall. No dependable connection tothe end wall was discovered.

Photo 5: Supper Room looking east into the Kitchen. The wall in the foreground is an unreinforcedpumice concrete block wall.

Photo 6: Supper Room roof space looking west at the timber roof beam and connection into theAuditorium column.

Photo 7: Timber sarking roof diaphragm running north/south in the north wing

Photo 8: Function Room looking south towards the North Wing. The wall/frame in the foregroundis the northern elevation of the North Wing.

Photo 9: Looking east in the Kitchen between grids B and C at the eastern end of the north wing.

Photo 10: Main Auditorium Looking west.

Photo 12: Auditorium roof trusses on the northern side of the Auditorium.

Photo 11: Heavy cables in the Auditorium roof space, at the eastern end.

Photo 13: Main Auditorium roof space looking south along a cut made in the timber sarking roofdiaphragm. Cut out dimensions are: 400mm wide x 8000mm long.

Photo 14: South western side (grid H and grid 4) of the Fly Tower, looking west.

Photo 15: Dressing Room/ Back of House column on the eastern elevation of the Fly Tower (Gridline 2). Deformed bars as shown in the drawings.


5640377 // NZ1-14797867-19 0.19 // 43

Appendix E

Structural Drawings

Provided separately due to the

large number of drawings


5640377 // NZ1-14797867-19 0.19 // 44