Download Sign of the Takahe Detailed Engineering Evaluation Report

Project 5810 – 5th October 2011
Sign of the Takahe
Detailed Engineering Evaluation Report
Qualitative Assessment
strategy • engineering • design
Contents
Introduction ...................................................................................................................... 3
Limitations of Report .......................................................................................................... 3
Executive Summary and Recommendations .......................................................................... 4
1
Statutory Regulations concerning Existing and Earthquake-prone Buildings ........................ 5
1.1
Building Act Requirements ......................................................................................... 5
1.2
Christchurch City Council (CCC) Requirements for Earthquake-Prone Buildings ................ 6
1.3
Recent Seismicity changes for Christchurch ................................................................. 6
2
Building Description ..................................................................................................... 7
2.1
General description ............................................................................................... 7
2.2
Structural System ................................................................................................. 7
3
Scope of Investigation ................................................................................................. 8
4
Building Performance in recent Canterbury Earthquakes ................................................... 9
4.1
Earthquake Damage .............................................................................................. 9
4.2
Review of Building Performance .............................................................................. 9
4.3
Critical Structural Weaknesses .............................................................................. 10
4.4
Areas Requiring Further Investigation .................................................................... 10
5
Seismic Assessment .................................................................................................. 11
6
Earthquake Repairs and Strengthening Work ................................................................ 12
6.1
Repairs .............................................................................................................. 12
6.2
Strengthening to 67% NBS ................................................................................... 13
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
Appendix
A : Christchurch City Council Compliance Schedule ................................................
B : Photos of damage .........................................................................................
C : Marked-up sketches of damage ......................................................................
D : Floor Level Survey ........................................................................................
E : Geotechnical Report ......................................................................................
F : Reference Material for Repair Works ................................................................
G : Proposed strengthening work to 67%NBS .......................................................
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20
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strategy • engineering • design
studio2 limited
5 norwich quay
po box 9
lyttelton
christchurch
new zealand
5th October 2011
tel:+64 3 929 0253
[email protected]
www.structex.co.nz
Justin Roberts
Insight Unlimited
Project & Construction Managers
Email: [email protected]
Dear Justin,
Re: Sign of the Takahe
Detailed Engineering Evaluation – Qualitative Assessment
Introduction
Structex has been engaged to complete a detailed engineering evaluation for the Sign of the
Takahe building at 200 Hackthorne Road, Cashmere, Christchurch. This report summarises the
findings of our qualitative assessment, which was undertaken in accordance with guidelines
prepared by the Post-Canterbury earthquake Engineering Advisory Group (EAG). At the time of
writing this report, these guidelines were in draft format (revision 5, released through CSG, 19th
July 2011) and under review with the Department of Building and Housing (DBH). Strength
assessment and strengthening options proposed herein are subject to a quantitative assessment
which is to follow. More specifically, this report:
(a) Highlights Building Act requirements and the Christchurch City Council policy for
earthquake-prone buildings
(b) Describes the existing building, its construction, and structural system
(c)
Outlines the level of investigation undertaken and where information was obtained
(d) Summarises earthquake damage caused by the recent Canterbury earthquakes
(e) Reviews the building’s performance in the recent Canterbury earthquakes
(f)
Identifies critical structural weaknesses
(g) Estimates the building’s seismic strength relative to New Building Standard (NBS),
commonly referred to as “current code”
(h) Outlines repairs to restore the building to its pre-earthquake condition
(i)
Proposes preliminary options to strengthen the building to 67% of current code
Limitations of Report
Findings presented as part of this report are for the sole use of our client, as addressed above.
The findings are not intended for use by other parties, and may not contain sufficient information
for the purposes of other parties or other uses. Our professional services are performed using a
degree of care and skill normally exercised, under similar circumstances, by reputable consultants
practicing in this field at this time. No other warranty, expressed or implied, is made as to
the professional advice presented in this report.
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Executive Summary and Recommendations
The Sign of the Takahe building has been damaged as a result of the recent Canterbury
earthquakes. This report summarises our detailed engineering evaluation of the building following
these earthquakes. A qualitative assessment has been carried out, with a quantitative
assessment to follow.
Damage to the building included cracking to stone masonry walls through-out, loss of several
stones from parapets, the north-west chimney and arches. Overall the building performed as is
typical for its age and type of construction.
From a review of existing drawings and visual inspections of the building, the following critical
structural weaknesses were identified:
Out-of-plane collapse of stone masonry walls as a result of wall connections to the roof or
floor structure failing.
Out-of-plane failure of stone masonry walls poses a hazard to persons outside of the building and,
if the wall that fails supports the roof, poses a hazard to building occupants. The north-west
gable-end wall in particular has been identified as being as risk to out-of-plane failure.
The building as it currently stands has an estimated seismic strength of 15% of new building
standard (NBS), and is therefore considered to be earthquake-prone. The quantitative
assessment will provide a more rational estimate and will help identify areas that will require
strengthening.
Options to repair the building involve reinstating lost stone blocks, stitching cracks with Helifix
Helibars, securing arches with Helifix ties, and re-pointing damaged mortar.
To strengthen the building to 67% of code, additional work is required in the form of new
diaphragm-wall connections, pinning of parapets with stainless steel threaded rods, strengthened
chimneys, new plywood diaphragms and steel framing to provide in-plane and out-of-plane
strengthening to stone masonry walls. In lieu of steel framing, the building could also be
strengthened through base isolation. This is likely to reduce the level of strengthening required to
the rest of the building and, pending further investigation, has the potential to be more costeffective.
The building is listed as a category 1 heritage building in both the Christchurch City Plan the
Historic Places Trust register. Therefore repair and strengthening works will be subject to
resource consent requirements.
Following recommendations/outcomes from the quantitative assessment, the level of
strengthening should be discussed with the building owner and insurer, and may require further
discussions with the Christchurch City Council. Once the level of strengthening has been agreed
and any other specified structural alteration work has been defined, we can begin the detailed
design and document the work for Building Consent and tendering.
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1
Statutory Regulations concerning Existing and Earthquake-prone Buildings
This section highlights statutory requirements concerning existing and earthquake-prone
buildings as laid out in the Building Act 2004, Building Code, and the Christchurch City Council’s
Earthquake-prone Building Policy 2010.
1.1
Building Act Requirements
The Building Act 2004 came into force on 31 March 2005 along with the Building Regulations. In
considering the structure of existing buildings the relevant sections of the Act are as follows:
Section 124 – Powers of territorial authorities in respect of dangerous, earthquake-prone, or
insanitary buildings
If the Territorial authority is satisfied that a building is dangerous or earthquake prone, the
Territorial Authority may:
(a) Put up a hoarding or fence to prevent people approaching the building;
(b) Place a notice on the building warning people not to approach the building, or
(c) Give written notice requiring work to be carried out on the building to reduce or
remove the danger.
Section 122 – Meaning of earthquake-prone building
This section of the Act deems a building earthquake prone if its ultimate strength capacity
would be exceeded, and the building would be likely to collapse causing injury or death, in a
“moderate earthquake”. The size of a “moderate earthquake” is defined in the Building
Regulations as one third the size of the earthquake used to design a new building at that
site.
Section 112 – Alterations to Existing Buildings
This section requires that after any alterations, the building shall continue to comply with
the structural provisions of the Building Code to at least the same extent as before the
alteration. This means that alteration work cannot weaken the building. Additional building
strength would therefore be required where structural elements are to be removed or
weakened, or additional mass to be added. The building will also need to be assessed in
terms of the egress from fire, and access for persons with disabilities provisions of the
Building Code and upgraded to comply, as nearly as is reasonably practicable.
Section 67- Waivers and Modifications
This section allows the Territorial Authority to grant a Building Consent subject to waivers or
modifications of the Building Code. The Territorial Authority may impose any conditions they
deem appropriate with respect to the waivers or modifications.
The Building Act was also altered by the Canterbury Earthquake (Building Act) Order 2010, which,
amongst other things, gave additional powers to the Territorial Authorities, extended the
definition of a dangerous building and extended the Schedule 1 list of building work exempt from
Building Consent.
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1.2
Christchurch City Council (CCC) Requirements for Earthquake-Prone Buildings
The Christchurch City Council adopted a new policy for earthquake-prone buildings in September
2010.
The policy reflects the Christchurch City Council’s determination to reduce earthquake risk to
buildings and ensure that Christchurch “is a safe and healthy place to live in” and may be viewed
on the CCC website.
In summary, the relevant items of the policy are as follows:
(a) Buildings are assessed using the New Zealand Society of Earthquake Engineering
(NZSEE) guidelines with applied loadings from AS/NZS 1170.5 and are classed as
earthquake prone if its strength is less than 33% of the applied loading from the loading
standard AS/NZS 1170.5.
(b) It outlines the Council’s approach to earthquake-prone buildings including identification,
prioritisation, timeframes and implementation. In general, Importance Level 4 buildings
(Post-disaster facilities, as defined by AS/NZS1170) will have 15 years from 1 July 2012
to either be strengthened or demolished. Importance Level 3 (crowd or high value)
buildings will have 20 years and Importance Level 2 (normal) buildings will have 30
years. There are also additional triggers for requiring assessment and strengthening work
to be undertaken at an earlier stage (including “significant” alterations or earthquake
damage).
(c)
The Council has a commitment to maintaining the intrinsic heritage values of Heritage
buildings and has some discretion with regards to strengthening levels and methods.
Each building will require discussion with Council Heritage team and Resource Consent
prior to any strengthening or repair works being undertaken.
To date the Council has identified 67% of New Building Standard (NBS), or current Code, as the
required level for strengthening of earthquake-prone buildings. However, the council may allow
strengthening to levels between 33% and 67%, on a case by case basis, taking into account the
following:
The cost of strengthening
Building use
Level of danger presented by the building
How much the building has been damaged
For buildings with a damaged building strength >33% of current code, it is recommended (but
not required) that the building also be strengthened.
1.3
Recent Seismicity changes for Christchurch
As a result of new information from the recent Canterbury earthquakes, changes have been made
to Section B1 of the Building Code, increasing seismic code levels within areas covered by the
Christchurch City, Selwyn District and Waimakariri District Councils. Such changes include:
Increasing the zone hazard factor (Z) in AS/NZS1170.5 from 0.22 to 0.3, and
serviceability limit state risk factor (Rs) from 1.25 to 1.33.
Replacing Section 5 of NZS3604:1999 with NZS3604:2011 Section 5, adopting Earthquake
Zone 2.
These changes came into effect on the 19th May 2011 and are interim code levels pending further
seismological study and investigation. For further information on other changes refer:
http://www.dbh.govt.nz/information-sheet-seismicity-changes.
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2
Building Description
2.1
General description
Building name:
Sign of the Takahe
Address:
200 Hackthorne Road, Cashmere, Christchurch
Building use:
Restaurant, Cafe and Bar
Heritage category:
1 (in both CCC City Plan and Historic Places Trust register)
Number of storeys:
Two
Roof construction
Slate tiles on timber trusses/rafters.
Wall construction:
Unreinforced stone masonry, with what appears to be a weak rubbleconcrete core.
Tongue and groove flooring on timber framing.
Floor construction:
Subfloor construction:
Year built:
Timber framing on shallow concrete piles, with perimeter stone
masonry foundation wall typically.
1918-1946
Approx. floor area:
627 m2
Building Importance:
2 (NZS1170.0)
The Conservation Plan prepared by
Dave Pearson Architects in 2006 notes
that the building was constructed in
stages as follows:
Stage 1: 1919
Stage 2: 1920-30
Stage 3: 1930-34
Stage 4: 1934-39
Stage 5: 1942-49
Figure 2.0: Stages of Construction
(Source: Dave Pearson Architects, 2006)
The Sign of the Takahe is listed in both the Christchurch City Plan and Historic Places Trust
register as a category 1 protected/heritage building. This means that repair and/or strengthening
work will be subject to resource consent requirements.
2.2
Structural System
The gravity load carrying system consists of timber framed floor and roof structures seated into
the stone work. The timber ground floor is supported on bearers, which are seated on shallow
concrete piles and the perimeter stone masonry foundation wall.
The lateral load carrying system consists of stone masonry walls providing in-plane restraint. Outof-plane stone masonry walls span vertically between floor and roof diaphragms, which transfer
the out-of-plane loads to in-plane wall lines. We note that existing floor/roof diaphragm
connections to walls are currently unlikely to be adequate to transfer these loads.
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3
Scope of Investigation
Our detailed engineering evaluation has been undertaken in accordance with Engineering
Advisory Group (EAG) guidelines “Guidance on Detailed Engineering Evaluation of Earthquake
Affected Non-residential Buildings in Canterbury”. At the time of writing this report, these
guidelines were in draft format (revision 5, released through CSG, 19th July 2011) and under
review with the Department of Building and Housing (DBH).
A qualitative assessment has been carried out, with the understanding that a quantitative
assessment will follow.
Our building evaluation and assessment has been based on the following information:
(a) Two visual inspections of the building carried out on the 6th July and 13th September
2011, which collectively included:
The exterior from ground level
The interior
The accessible roof space following access via a ceiling hatch in the south kitchen
The subfloor space under the cellar following access via a floor hatch
The northern part of the roof following access from a cherry-picker
(b) Limited architectural floor plans and elevations provided by Tony Ussher, which were
obtained from Dave Pearson Architects.
(c)
Geotechnical investigation and report (See Appendix E) provided by Land Development &
Exploration Ltd, which included:
A walkover visual assessment
(d) The following on-site investigations which were carried by Simon Construction Ltd:
A floor level survey of the first floor (Refer Appendix D)
6 no. core samples of internal and external stone masonry walls
Localised removal of tongue and groove flooring in the corners of the first floor
restaurant area and in the ground floor private sitting room.
Localised removal of slate roofing and copper guttering adjacent a chimney to
reveal roof framing connection to the stone masonry wall.
(e) The following reports prepared by others for the Christchurch City Council:
Conservation Plan, prepared by Dave Pearson Architects in 2006
Earthquake Report, prepared by Holmes Consulting Ltd in 2006
We highlight that the type of construction was obtained from a visual inspection of exposed
construction as listed above. Similar construction was then inferred for the rest of the building.
The following non-structural aspects fall outside the scope of this report and have not been
covered by this investigation and assessment:
Compliance items covered by the building Warrant of Fitness (A list of such items has been
included in Appendix A)
An electrical safety review
A fire safety review
These items should be inspected and assessed by qualified trades people or specialists prior to
the building being reoccupied or repair/strengthening works carried out. We request such persons
be instructed to identify loose and/or inadequate fixings, and to notify the engineers if these are
found.
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4
Building Performance in recent Canterbury Earthquakes
4.1
Earthquake Damage
Generally the building has suffered moderate damage in the form of cracking to stone masonry
walls and the loss of several parapet stones.
Damage observed is briefly described below. Photos and marked-up sketches are included in
Appendix B and Appendix C respectively to indicate the location and nature of the observed
damage. These are not meticulous or comprehensive records of all damage but have been
included to provide an indication of the damage.
Collapse of the north-west chimney on to the roof damaging adjacent slate tiles and
timber sarking underneath. The remaining chimneys have sections of cracked mortar near
their supports.
Isolated parapet stone blocks fell or were dislodged (mostly to east and south sides).
Remaining sections of the parapets have also cracked particularly at the corners. (Most of
the loose parapet stones have been lowered to the ground and stored on site as previously
instructed).
Cracks and some movement to exterior stone mortar joints and isolated locations of
spalling of the face of the stone. Cracks at the north-west gable indicate slight movement
of the gable away from the building towards the road.
Interior diagonal cracks, generally leading from re-entrant corners of windows and doors,
in stone and plaster coated walls at both levels throughout.
Isolated cracks to stone mortar joints and some stone spalling to decorative archway at
entrance foyer.
Cracks and dislodgement of keystone in arch between lounge and smoke room.
Cracking of lath and plaster ceilings, primarily to kitchen area.
Cracked mortar to stone blocks to east exterior archway at junction with building.
Partial collapse of dry stone wall on west side.
To date the following temporary securing work has been carried out:
Lowering of loose stone blocks.
Wales and ties to north-west and north-east gables.
Strapping and bracing of remaining chimneys, and protection of adjacent roofing.
Fence cordons around the entire building.
Propping of loose internal stone arch between lounge and smoke room.
The floor level survey undertaken by Simon Construction Ltd revealed floor slopes of typically less
than 0.25%. This is regarded as being small enough to be the result of construction technique as
oppose to earthquake damage. In isolated locations, floor slopes of up to 0.48% were recorded.
Given the age of the building, and the lack of apparent movement to the adjacent walls, we
believe these are more likely the result of construction technique than earthquake damage.
The geotechnical report prepared by Land Development & Exploration Ltd noted that there was no
damage related to deformation of the underlying soil and that additional geotechnical
investigation was not required.
4.2
Review of Building Performance
Generally the building responded as is typical for its age and type of construction. Mortar cracking
and partial/localised collapse is typical damage observed to unreinforced stone masonry
buildings. The rubble-concrete core in stone walls and apparent good condition of the mortar are
likely to have improved the seismic performance of the building, reducing the likelihood of partial
collapse.
Exposure of floor/roof diaphragm fixings to stone masonry walls suggests weak connections
between these elements. Typically, joists and beams appear to be simply seated into the
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stone work, providing a friction only connection. The only anchored fixing found was between the
north restaurant roof rafters and their adjacent east-west running walls. Drawings suggest each
of these rafters are anchored into the stone wall by three 20mm diameter threaded rods.
Given these weak connections, it is surprising out-of-plane failure of stone masonry walls did not
occur. The inadequacy of these connections is apparent in the north-west gable wall, which
appears to have moved away from the building. We believe out-of-plane failure of stone masonry
walls due to failure of these connections or a complete lack of connections is a risk.
Cracking to stone masonry occurred mainly around window, door and arch openings. Openings
and re-entrant corners create stress discontinuities where cracks are likely to initiate. Therefore
particular attention should be paid to each arch, door and window opening when scoping repair
work.
4.3
Critical Structural Weaknesses
From a review of architectural floor plans and visual inspections of the building, the following
potential critical structural weaknesses were identified:
Out-of-plane failure of stone masonry walls as a result of diaphragm-to-wall tie failure.
Out-of-plane failure of gable-end walls poses a fall hazard to persons outside the building. Given
the height of the building and proximity to Hackthorne and Dyers Pass Roads, the fall zone would
include both the footpath and at least one road lane.
Out-of-plane failure of non-gable-end walls supporting the roof poses a fall hazard to persons
outside the building, as well as persons within the building should the roof also collapse.
4.4
Areas Requiring Further Investigation
To date, only localised areas have been exposed to reveal hidden construction. This has been
sufficient to provide an indication of the type of construction for strength assessment purposes.
We expect there to be differences in diaphragm-wall connections between sections that were
constructed at different times. At a later date, all diaphragm-to-wall connections will need to be
exposed to allow new strengthened connections to be detailed on a case-by-case basis.
The foundation structure exposed revealed shallow piles under the cellar room area, but timber
piles bearing onto a concrete slab under the private sitting room. We understand that this area
was previously a concrete porch area. It would be useful to know the nature of the foundations to
the rest of the building, as this will influence options for strengthening. We recommend the
following:
Further removal of flooring in other areas – namely areas under the tramway shelter, rear
entrance, ground floor kitchen, and public refreshments area.
Break out of concrete slab under private sitting room adjacent stone masonry wall.
To allow strengthening to be detailed for existing chimneys, their condition, construction and
geometry will need to be confirmed with a camera and invasive investigation.
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5
Seismic Assessment
A seismic performance estimate for the Sign of the Takahe was undertaken by Holmes Consulting
Ltd in 2006. They estimated the building to be at 20% of new building standard (NBS) as at
2006.
Based on their assessment and given that current code levels in Christchurch have been
increased by 36% since 2006, we estimate the building be at 15% of the current NBS. Therefore
the building is regarded as being earthquake-prone in terms of the Building Act 2004 and the
Christchurch City Council Earthquake-prone Building Policy 2010. This means the building will
require strengthening to 67% of NBS as part of the earthquake repairs.
Structex has been engaged by Insight Unlimited to undertake a quantitative assessment of the
building. This is currently underway, and will provide a more refined assessment of the building
strength relative to current code. It will also highlight particular areas that will require
strengthening.
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6
Earthquake Repairs and Strengthening Work
This section describes repair works to restore the building to its pre-earthquake condition and
preliminary options to strengthen the building to 67% of current code. These options are subject
to change pending the quantitative assessment and further consultation with the council heritage
team, heritage architect, construction contractor and other specialists. In many cases, further
investigation of existing construction will be required (Refer Section 4.4).
6.1
Repairs
This section describes options of repair to restore the building to its pre-earthquake condition.
These repairs are subject to change as the works proceed and as further information regarding
existing construction and the extent of damage is revealed. On-site correspondence with the
contractor carrying out the works may be required.
The costs associated with the repairs will require assessment by a quantity surveyor and/or
qualified contractor who will need to visit the site to view the extent of damage and work
required.
General repairs to unreinforced stone masonry:
Stitch all cracks to stone masonry walls using Helifix Helibars. Install in accordance with
Helifix literature (Refer Appendix F). We recommend contacting Helifix to provide specific
guidance on product selection, bar spacing and installation.
Rake-out internal and external damaged mortar and re-point. The mortar colour (where
exposed) and strength should match the existing and be weaker than the adjacent stone,
provisionally 8 MPa.
After mortar has been raked out but before re-pointing, we recommend a qualified stone
mason is engaged to inspect the internal mortar. Where mortar is in a poor condition, fill
with grout.
Reinstate dry-stone masonry wall in courtyard. Strengthening could be considered.
Repairs to stone arches and parapets:
Reinstate displaced parapet and internal archway blocks reusing stones where possible and
replacing broken stones to match previous where necessary (in conjunction with
discussions with the Heritage Architect). Breakout interior and exterior cracked mortarjoints and re-point as above.
Secure arches with Helifix Helibars and Dryfix ties or CemTies in accordance with Helifix
literature.
Repair to plaster rendered stone walls:
Repair cracked plaster rendered stone walls by breaking out plaster, re-pointing mortar as
above and re-plastering to match the original, utilising fibreglass mesh reinforcement.
Repair to lath and plaster lined walls/ceilings:
For minor isolated cracks (smaller than 300mm in any direction), grind-out V-shaped
groove along crack. Re-plaster over groove, utilising fibreglass mesh reinforcement across
the crack.
For larger cracks/fractures to plaster linings, remove and replace with GIB in accordance
with GIB literature.
Sand, prime and repaint over to match existing.
Repair to chimney:
We recommend the replacement chimney be a strengthened version. Refer Section 6.2.
Other non-structural repairs:
Ease and adjust any jammed/catching doors/windows/etc.
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6.2
Realign and re-fix any dislodged timber architraves, frames, skirting boards and trims.
Sand, prime and repaint over to match existing.
Repair/replace broken windows and frames as required.
Strengthening to 67% NBS
In addition to the repairs outlined in the previous section, the following are preliminary options to
strengthen the building to 67% of current code. Refer attached sketches in Appendix G for further
details.
Option 1: Conventional strengthening with additional structure
Strengthening to stone masonry walls:
In-plane strengthening could be provided in the form of new steel frames and foundation
beams.
Out-of-plane strengthening could be provided in the form of vertical steel mullions where
required.
Such framing could be concealed by framing against internal stone walls and lining over
with GIB. This will however conceal the internal stone work that is currently exposed.
Strengthening to floor/roof diaphragms:
Strengthening to roof diaphragms could take the form of:
a. Steel Reid braces and SHS struts in the northern restaurant area. These could be
painted black to minimise their visual impact.
b. New plywood ceiling diaphragms in the southern kitchen area which currently has a
lath and plaster ceiling.
c. Either plywood ceiling/roof overlays or steel bracing to the remaining areas.
Floor diaphragms could be strengthening with new plywood diaphragms installed under
tongue and groove flooring or as a new ceiling underneath.
Strengthening to diaphragm-wall connections:
New fixings tying stone masonry walls into the floor/roof diaphragm will be required.
These are likely to be in the form of M16 stainless steel threaded rods through floor/roof
framing, either drilled and epoxy grouted into inside face of stone to within 50mm of
outside face, or full depth of the wall with a washer on the exterior face.
Strengthening to parapets:
Strengthen parapets with M12 stainless steel (316) threaded rod, core drilled and epoxy
grouted in place at 400mm centres typically and as per attached sketches. The diameter of
the hole should be 18-20mm grouted with Hilti HIT-HY150 epoxy. The surface of the holes
should be capped with stone plugs to minimise visual impact and allow even wearing.
Anchor parapets into roof structure with M16 stainless steel threaded rods either drilled
and epoxy grouted into inside face of stone to within 50mm of outside face, or full depth of
the wall with a washer on the exterior face. Preliminary design has found that exterior
washers at 600mm centres will likely allow the parapet to be strengthened to 67% of
current code, and that drilling and epoxy grouting will likely allow strengthening to a lower
value (possibly 57% of current code). Confirmation of wall makeup, anchor depth and roof
framing geometry will allow this to be verified. Testing of anchors on site would also allow
more accurate (and less conservative) strength values to be used (refer attached from
2006 NZSEE guidelines).
Strengthening to chimneys:
Reinstate north-west chimney to match original. Anchor reinstated blocks with M12
stainless steel (316) threaded rod, core drilled and epoxy grouted in place as per attached
sketches
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Strengthen chimneys with galvanised CHS tube grouted in place, and tie into adjacent roof
structure as per attached sketches. Breakout cracked stone mortar and repoint.
Alternative methods to strengthen the chimneys include:
a. Interior post-tensioning. Provide concrete anchor blocks top and bottom of chimney
and install pre-greased and sheathed 12.7mm strands inside chimney. Allow for 78 strands per chimney.
b. Exterior post-tensioning. Bolt steel angles near top and bottom of chimneys and
post-tension with 4-D20 Macalloy bars or similar.
c. Interior reinforced concrete. Install reinforcing steel cage up chimney and grout fill.
Depending on the size of the chimney cavity a new flue may be able to be installed.
d. Demolish chimneys and reconstruct as stone veneers around steel frames.
Option 2: Strengthening with base isolation
As an alternative to conventional strengthening, the building could be strengthened with base
isolation. Base isolation effectively reduces the seismic force demand within the building by
creating an isolation plane below the building, such that the ground moves underneath, whilst the
building remains comparatively still.
As base isolation reduces seismic demands to the building, it has the advantage of reducing the
level of strengthening that would be required the structure above the isolation plane. For
example, with base isolation, strengthening to stone masonry walls listed above will not be
required. Strengthening to diaphragm-wall connections and chimneys will still be required, but to
a lesser extent. Whether strengthening will still be needed to parapets and floor diaphragms are
subject to further investigation and base isolation design.
As the building is heavy, squat and founded upon rock, it presents itself as an ideal candidate for
base isolation. In addition, base isolation is often more cost effective than conventional
strengthening when it comes to retrofit of existing buildings. At this stage, two factors have been
identified which could negate this, which should be confirmed with further investigation prior to
proceeding with base isolation design:
Identification of a suitable isolation plane. Investigations under the ground floor cellar
indicate a subfloor space that could be used as an isolation plane. The full extent of the
subfloor space in the northern and southern ends of the building however is unknown.
Near fault effects reduce the effectiveness of base isolation. Near fault effects is a
phenomenon which can be described as a long period acceleration pulse, which occurs at
sites close to the ruptured fault. A site specific analysis will be needed to assess near fault
effects from newly traced faults in the Christchurch area. Such services are typically
provided by specialised geotechnical engineers and seismologists such as GNS. Usually
near-fault effects can be designed for in base isolation, for example, Supreme Court and
Parliament Buildings in Wellington which have near fault effects.
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If you have any queries regarding the above Structural Assessment Report, please do not
hesitate to contact the undersigned.
Yours sincerely,
Studio2 Ltd
Reviewed by,
Studio2 Ltd
Euving Au
B.E.(hons), M.E., GIPENZ
Structural Engineer
Studio2 Limited
Will Lomax
B.Eng(hons), IntPE, CPEng#226903
Director
Studio2 Limited
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Appendix A: Christchurch City Council Compliance Schedule
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Appendix B: Photos of damage
Sign of the Takahe – East elevation
Sign of the Takahe – South-west elevation
Loss of parapet stone
Mortar cracking to external arch
Collapse of chimney, loosening of parapet
stone, damage to slate roofing
Movement and damage to external arch
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Mortar cracking to internal decorative arch near
restaurant entrance
Cracking to stone masonry around window
opening
Cracking to stone masonry arch above window
Cracking and loosening of stone forming
doorway arch
Mortar cracking to stone masonry wall
Cracking to plaster render over stone work
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Cracking above doorway arch
Cracking above doorway arch
Diagonal cracking to plaster rendered stone
masonry
Diagonal cracking to plaster rendered stone
masonry
Diagonal cracking to plaster rendered stone
masonry
Diagonal cracking to plaster rendered stone
masonry
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Appendix C: Marked-up sketches of damage
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Appendix D: Floor Level Survey
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Appendix E: Geotechnical Report
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Project Reference: 10048
12 July 2011
Christchurch City Council
C/o Insight Unlimited
P.O. Box 1219
GISBORNE
Attention: John Radburn
Dear John
SIGN OF THE TAKAHE
PRELIMINARY GEOTECHNICAL ASSESSMENT REPORT
1 I NTRODUCTION
Land Development & Exploration Ltd was engaged by Insight Unlimited on behalf of
Christchurch City Council to undertake a visual assessment of the Sign of the Takahe which
was damaged by the February earthquake event. The purpose of the work was to assess
whether ground deformation contributed to the damage to the building, and what
geotechnical engineering work may be required to reinstate the building and land back to a
satisfactory condition. Provision of possible engineering solutions to minimise damage to
the assets from future earthquake events was also an objective.
2 A SSESSMENT
The visual assessment was undertaken by Georg Winkler; a senior Chartered Professional
Engineer with a background in engineering geology and geotechnical engineering, and the
director of a team responsible for the mapping and understanding of earthquake induced
lateral spreading throughout Christchurch for the Earthquake Commission. Georg was
accompanied by John Radburn of Insight Unlimited.
3 S ITUATION
The Sign of the Takahe is located on a Port Hills ridgeline approximately half way up Dyers
Pass Road.
Land Development & Exploration Ltd, P.O. Box 671, Gisborne, New Zealand
Ph (06) 8673035, Fax (06) 8673037, www.lde.co.nz
Christchurch City Council
Sign of the Takahe
Preliminary Geotechnical Assessment Report
Based on the walkover assessment undertaken, there does not appear to be any damage
to the structure that is related to earthquake-induced deformation of the underlying
ground.
Accordingly, there are no geotechnical recommendations to be made, and we do not
consider that additional geotechnical investigation work will be required.
4 O THER C ONSIDERATIONS
This report was prepared for Christchurch City Council with respect to the particular brief
given to us. Information contained in it can not be used for other purposes or by other
entities without our prior review and written consent.
It should be appreciated that the report is based on a visual assessment and observations
made in a regional context and that the nature and behaviour of the subsurface materials
may vary from that described following further investigation and analysis.
Project Ref: 10048
-2-
Christchurch City Council
Sign of the Takahe
Preliminary Geotechnical Assessment Report
Yours faithfully
LAND DEVELOPMENT & EXPLORATION LTD
Georg Winkler
MIPENZ, CPEng
Geological-geotechnical engineer
\\sbs\documents\LDE Projects\10000 to 10100\10048 Insight Chch Building Investigations\Sign of the Takahe\10048gew12072011 Sign of the Takahe
Preliminary Assessment Report R1.doc
Project Ref: 10048
-3-
Appendix F: Reference Material for Repair Works
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REPAIR DETAILS NZ-CS11
NZ-CS11
Product
Repair of a crack near a corner in
a stone wall using HeliBars
Description
Code
HeliBar
Grade 316 stainless steel reinforcement
HBR
HeliBond
Injectable cementitious grout
HLB
HeliPrimer
Water-based primer for porous substrates HWB
CrackBond Epoxy resin for filling cracks
HCB
METHOD STATEMENT
1. Using an appropriate power cutting tool with vacuum
attachment, cut slots into the horizontal mortar joints, to the
specified depth and at the required vertical spacing.* Ensure
that as much mortar is removed as possible from the exposed
surfaces in order to provide a good masonry/grout bond. This
operation may require the use of hand tools to remove the
mortar due to the random nature of the stone.
2. Clean out all dust and loose mortar from the slots and
thoroughly flush with water. Where the substrate is very porous
or flushing with water is inappropriate, use HeliPrimer WB.
Ensure the slot is damp or primed prior to commencing step 5.
3. Mix HeliBond cementitious grout thoroughly using a drill and
mixing paddle and load into the Helifix Pointing Gun.
RECOMMENDED TOOLING
For cutting slots.........................Chisel, mortar saw (e.g. Arbortech All Saw) or
angle grinder with dust guard (e.g. C-Tec) and vacuum
For mixing HeliBond .................................................Drill with mixing paddle
For injection of HeliBond into slots.................................Helifix Pointing Gun
with mortar nozzle
For smoothing pointing.................................................Standard finger trowel
* Specification Notes
4. Fit the mortar nozzle to the pointing gun.
5. Inject a bead of HeliBond grout, 10-15mm deep, into the back
of the slot.
The following criteria are to be used unless specified otherwise:
6. Push the 6mm HeliBar into the grout to obtain good coverage.
A. Allow for the installation of one HeliBar for each 100mm of wall thickness
into each cut slot. By example, a common 200mm solid stone wall
construction will require the installation of two HeliBars per slot. A 300mm
solid wall construction will require three Helibars per slot.
7. Repeat steps 5 and 6 as required to install all specified HeliBars
into the slot.
B. Depth of slot into a common 200mm stone wall to be 35mm to 40mm. Add
10mm for each additional 100mm of wall thickness.
8. Inject a final bead of HeliBond grout over the exposed HeliBar
and iron it into the slot using a finger trowel. Inject additional
HeliBond grout as necessary, leaving 10-15mm for new
pointing.
C. Height of slot to equal full mortar joint height, with a minimum of 8mm.
D. HeliBar to be long enough to extend a minimum of 500mm either side of
the crack or 500mm beyond the outer cracks if two or more adjacent cracks
are being stitched using one rod.
9. Point up the remaining slot with a suitable matching mortar
and make good the crack using an appropriate Helifix bonding
agent or filler, e.g. CrackBond, depending on the width of the
crack.
F. Where a crack is less than 300mm from the end of a wall or an opening the
HeliBar is to be continued for at least 100mm around the corner and
bonded into the adjoining wall or bent back and fixed into the reveal,
avoiding any DPC.
10. Clean tools with clean, fresh water.
NOTE. Pointing may be carried out as soon as is convenient after
the HeliBond has started to gel. Ensure that pointing does not
disturb the masonry/HeliBond connection.
CAUTION. Always locate, identify and isolate any electrical, water
or gas services which may be present in the wall or the wall cavities
and can pose a safety risk before drilling or cutting. Always take
the necessary safety precautions. Use electrical safety gloves and
wear appropriate footwear and eyewear.
E. Normal vertical spacing is 425mm.
G. In hot conditions ensure the masonry is well wetted or primed to prevent
premature drying of the HeliBond due to rapid de-watering. Ideally
additional wetting of the slot, or priming with HeliPrimer WB, should be
carried out just prior to injecting the HeliBond grout.
The above specification notes are for general guidance only and Helifix
reserves the right to amend details/notes as necessary.
GENERAL NOTES
l
l
Helifix product details available at www.helifix.co.nz
If your application differs from this repair detail or you require specific
technical information, call Helifix on (03) 376 5205.
Helifix (New Zealand) Limited
U4/28 Tanya Street l Bromley l Christchurch l New Zealand
E-mail: [email protected]
Web: www.helifix.co.nz
l
8062
Tel. (03) 376 5205
Copyright © Helifix Limited 2010
REPAIR DETAIL NZ-LR10
NZ-LR10
Stabilising failed brick arch lintels
using HeliBars and CemTies
Product
Description
Code
HeliBar
Grade 316 stainless steel reinforcement
HBR
CemTie
Grade 316 stainless steel structural pin
HCT
HeliBond
Injectable cementitious grout
HLB
HeliPrimer Water-based primer for porous substrates HWB
METHOD STATEMENT
1. Using an appropriate power cutting tool with vacuum
attachment, cut slots into the horizontal mortar joints, to the
specified depth and at the required vertical spacing.* If the
wall is plastered/rendered and the mortar joints are not visible,
cut the horizontal slots through any plaster/render and into the
masonry. Ensure that as much mortar is removed as possible
from the exposed brick surfaces in order to provide a good
masonry/grout bond.
2. Mark the positions for the CemTie holes on the underside of
the soldier course.
3. Drill 14–16mm ø clearance holes at the required angle and to
the specified depth.* The angle of drilling should be such that
the hole will pass behind the lower HeliBars and penetrate at
least 50mm into the course of masonry above the reinforcing.
RECOMMENDED TOOLING
For cutting slots.........................Chisel, mortar saw (e.g. Arbortech All Saw) or
angle grinder with dust guard (e.g. C-Tec) and vacuum
For drilling ................................................SDS rotary hammer drill 650/850w
For mixing HeliBond .................................................Drill with mixing paddle
For injection of HeliBond into slots.................................Helifix Pointing Gun
with mortar nozzle
For insertion of the CemTies ....................................Helifix Pointing Gun with
CemTie Pinning Nozzle
4. Clean out all dust and loose mortar from the slots and holes
and thoroughly flush with water. Where the substrate is very
porous or flushing with water is inappropriate, use HeliPrimer
WB. Ensure the slot and holes are damp or primed prior to
commencing steps 7 and 15.
For smoothing pointing.................................................Standard finger trowel
5. Mix HeliBond cementitious grout thoroughly using a drill and
mixing paddle and load into the Helifix Pointing Gun.
12. Repeat steps 7 to 11 for the lower slot.
A. Depth of slot into masonry to 40mm to 55mm.
B. Height of slot to equal full mortar joint height, with a minimum of 8mm.
C. Top and bottom reinforcements should be positioned as far apart as
practicable, up to a maximum distance equivalent to 10 brick courses
(approx. 850mm).
D. HeliBar to be long enough to extend a minimum of 500mm beyond each
side of the opening.
E. Any fractures in the masonry within the ‘beam zone’ MUST be stabilised by
crack stitching (see Repair Detail NZ-CS01), CrackBond or masonry
replacement.
F. Any missing or very poor quality masonry MUST be replaced.
G. CemTie length to be sufficient to penetrate at least 50mm into the course of
masonry above the reinforcement.
H. Depth of hole to be CemTie length + 25mm.
I. In hot conditions ensure the masonry is well wetted or primed to prevent
premature drying of the HeliBond due to rapid de-watering. Ideally
additional wetting of the slots and holes, or priming with HeliPrimer WB,
should be carried out just prior to injecting the HeliBond.
13. Attach the required length of CemTie pinning nozzle to the
pointing gun and pump grout to fill the nozzle.
The above specification notes are for general guidance only and Helifix
reserves the right to amend details/notes as necessary.
6. Fit the mortar nozzle to the pointing gun.
7. Inject a bead of HeliBond cementitious grout, 10-15mm deep,
into the back of the slot.
8. Push the first 6mm HeliBar into the grout to obtain good
coverage.
9. Inject a second bead of HeliBond grout over the exposed
HeliBar.
10. Push the second 6mm HeliBar into the grout to obtain good
coverage.
11. Inject a third bead of HeliBond grout over the exposed HeliBar
and iron it into the slot using a finger trowel. Inject additional
HeliBond as necessary, leaving 10-15mm for new pointing.
* Specification Notes
The following criteria are to be used unless specified otherwise:
14. Wind the CemTie into the nozzle and ensure that it is fully
covered in grout.
15. Insert the nozzle to the full depth of the drilled hole and pump
the CemTie and grout.
16. Repeat steps 13 to 15 for each hole.
17. Make good the CemTie holes and point up the remaining slots
with a suitable matching mortar.
GENERAL NOTES
l
l
Helifix product details available at www.helifix.co.nz.
If your application differs from this repair detail or you require specific
technical information, call Helifix on (03) 376 5205.
18. Clean tools with clean, fresh water.
NOTE. Pointing may be carried out as soon as is convenient after
the HeliBond has started to gel. Ensure that pointing does not
disturb the masonry/HeliBond connection.
HELIFIX (new zealand) LIMITED
Unit 4, 28 Tanya Street l Bromley l Christchurch l 8062
TEL. (03) 376 5205
Copyright © Helifix Limited 2010
Appendix G: Proposed strengthening work to 67%NBS
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Legislative and Regulatory Issues - Appendix 2B
Factors to be considered when evaluating “as near as is reasonably practicable to that of a new building”
10B.4
Tests on Connectors
10B.4.1
Default Strength for Bolts
The following Table 10B.2 lists design strengths that may be adopted for bolts connecting
components to masonry. Larger values may be adopted if justified by tests conducted in
accordance with b).
Table 10B.2:
Item
1
2
Default connector strengths
Type
Shear Connectors
Comment
Strength
Bolts should be centred in an
oversized hole with nonshrink grout or epoxy resin
grout
around
the
circumference.
Shear bolts and shear dowels
M12 bolt: 6 kN
embedded at least 200 mm
M16 bolt: 9 kN
into unreinforced masonry
M20 bolt: 14 kN
walls.
Tension Connectors
The designer should also
ensure that the connection to
other
components
is
adequate.
0.7
0.7
25% of all new anchors
should be tested to the
following torques:
—M12: 54 Nm
—M16: 68 Nm
—M20: 100 Nm
Tension bolts extending
entirely through the masonry,
and secured with a bearing
plate at least 138 x 138 or
155 diameter.
Tension bolts and reinforcing
bars grouted (cementitious or
epoxy resin) 50 mm less
than the thickness of the
masonry
10B.4.2
29 kN (all sizes)
Bolts grouted with epoxy 11 kN (all sizes)
may lose strength and fail
abruptly id wall cracking
occurs at the bolt.
The
designer should ensure that
failure cones from adjacent
bolts do not overlap.
Tension strength of anchors
This section outlines procedures for preliminary testing where the designer may wish to conduct
tests on new anchors to derive greater design values than suggested in Table 10B.2.
Appendices
30/06/2006
App-84
Legislative and Regulatory Issues - Appendix 2B
Factors to be considered when evaluating “as near as is reasonably practicable to that of a new building”
Application of load and determination of results
The masonry wall should support the test apparatus. The distance between the anchor and the test
apparatus support should not be less than the wall thickness. The tension test load reported should
be the load recorded at 3 mm relative movement of the anchor and the adjacent masonry surface.
For the testing of existing anchors, a preload of 1.5 kN shall be applied prior to establishing a
datum for recording elongation. Anchors should be installed in the same manner and using the
same materials as intended to be used in the actual construction.
Test frequency
A minimum of five tests for each bolt size and type should be undertaken.
Determination of design values from tests
The ultimate limit state strength of tested existing wall anchors should be taken as the mean of all
results less 0.8 times the standard deviation for each bolt size. A strength reduction factor of 0.7
should be used to determine the design strength.
Appendices
30/06/2006
App-85