A REVOLUTION IN STRUCTURAL TIMBER GRADING
Douglas Gaunt 1
ABSTRACT; New Zealand has seen a transformation in the way it produces structural timber with the widespread
adoption of machine stress grading along with the introduction of third party auditing. In conjunction with this the
opportunity arose to align the properties of forest resource with the design demands of light timber framed houses. The
final outcome of these changes has considerably enhanced New Zealand’s structural timbers reputation
KEYWORDS: Structural timber, Machine grading, Quality Control, Timber design
1. INTRODUCTION
Over the last ten years New Zealand has seen a
transformation in the way structural timber has been
graded, marketed, used and quality controlled.
Prior to 2000 the majority of structural timber was
visually graded with only a few large producers
investing in machine stress grading. The machine stress
grading machines used were the traditional plank
bending types ie. Metriguards, Computermatics and
Eldeco Darts, five machines were regularly used in
production with few others in storage.
At this time the most common structural grades were the
NZ visual grades of Engineering No 1Framing & No 2
Framing grades with Carter Holt Harvey having recently
introduced the Australian MGP10 grade into New
Zealand called Laserframe
The application of quality assurance (QA) to structural
timber was in its infancy with the two large producers
(Carter Holt Harvey and Fletcher Challenge) using in
house output control systems. However the QA
procedures did not have an independent third party
auditing component.
Scion had undertaken several large evaluations of the NZ
Radiata pine resource and it had become apparent that
the simple introduction of the Australia MGP grades
(MGP10, 12 & 15) would not be the best solution. The
MGP grading system was developed in Australia
specifically for the machine stress grading of pine. did
not match well the strength and stiffness properties of
the NZ Radiata pine resource however the principle
behind the MGP grading system was still valid.
In terms of the structural use of Radiata pine particularly
in house construction, the grade of choice for tens of
years had been No1 Framing, this was assigned a
Modulus of Elasticity (MoE) of 8GPa. The housing
builders and developers had a long history of what
timber was needed where and the costs to build a house.
Structural timber had also received some bad press with
the prosecution of a major producer over its failure to
produce timber with the required structural properties.
1
Scion, Private Bag 3020 New Zealand.
douglas.gaunt @scionresearch.com
To address all these issues it became apparent that
significant changes would be required if NZ wanted to
lift structural timbers reputation both within NZ and
internationally.
This could only be done by keeping within a tight series
of financial and end user impact constraints. These
being:
• The need to fit the structural grades around the
actual properties of our current and future
Radiata pine resources.
• A form of quality assurance focusing on output
control of structural properties as opposed to
machine control complete with third party
auditing. The application of the QA procedures
had to be made as simple and practical as
possible if widespread adoption was going to
occur.
• Any new structural grades could not afford to
significantly alter the way houses were built or
more importantly the cost to build a house.
• Was it possible to bring in new grading
technologies that reduce both the capital
and/operational costs whilst providing enhanced
returns to the wood processor?.
The Approach taken to address this case is outlined as
follows
• Structural grades – the development of new
structural grades link forest to end use.
• NZS3622 Structural property verification – the
introduction of quality control and third party
auditing.
• New Acoustic grading technology,
• A summary of the changes as of 2012.
Presently in New Zealand work is underway on a model
that can take all the following inputs: site, silviculture,
age, genetics, log form and position in tree, distribution
of branches, Sawing pattern, Piece position in Log, etc..
to make gross predictions of structural grade recovery.
A fully integrated model such as this may in fact not be
achievable without the allocation of huge resources
(many millions of dollars). However we do have a good
understanding on what variables affect the outturn of
structural grades. In broad terms the following Figure 1
shows the key factors that influence lumber grade
recovery (and wood quality in general).
Site
Silviculture
Fertility
etc..
Thinning
Stocking
Branch Size
etc..
Wood Quality
Lumber grade recovery
in this case
Age of Harvest
(20,30 or 40 years)
Genetics
Wood Density
Growth rate
etc..
Figure 1: Key Factors affecting Wood Quality
It is unlikely that a model will ever exist that can reliably
predict the strength and stiffness values of individual
boards.
Accordingly the approach required is to
select/grade at several points along the processing chain.
Several nationwide studies were undertaken exploring
the stiffness and strength properties of radiata pine
[1,2,3,4]. These studies generally involved purchasing
visually graded timber in the No1Framing and No2
Framing structural grades The timber was then checked
for visual grading accuracy, machine stress graded and
then tested for bending strength and stiffness
In 1999 Figure 2 [1] was produced which showed the
relationship between the bending strength/stiffness and
the Australian MGP & F grades and the then suggested
MGP6 & 8 grades.
Figure 2: 1999 Grade relationships
150x50 and greater
100x50 and smaller
Key
Characteristic Bending Strength, MPa
2. STRUCTURAL GRADES.
Structural lumber requires quantitative performance
measures of stiffness and strength which designers can
use with confidence. Traditionally these properties had
been provided for through a set of visual grading rules
which were linked to a set of characteristic grade
stresses. However the grade recoveries in visual grading
were declining and visual grading did not directly
measure stiffness – Visually graded No.1 framing not
always well graded. Surveys (Forest Research,
Consumer Institute) found serious percentages of pieces
out of grade within packets. generally the most important
characteristic in timber design [1].
45
MGP 15
40
F14
Present 'F' grades
35
Present 'MGP' grades
F11
30 Bulk of Resource
25
F7
20
MGP 12
F8
MGP 10
F5
15
F4
MGP 8
MGP 6
10
Proposed 'MGP8 & 6' grades
5
0
4
6
8
10
12
14
16
Modulus of Elasticity GPa
Data points shown represent recent Forest
Research radiata pine structural evaluations
In Figure 2 New Zealand Radiata pine can be broadly
characterised by its relatively high stiffness for a given
strength or conversely a lower strength for given
stiffness. This characteristic also agrees with the
rationale behind the development of the Australia
developed MGP grades (MGP10, 12 & 15). Previously
Australian pine had been graded into the F grades that
historically were developed for Australian hardwoods
which have a high strength for given stiffness. Using the
F grade system on Radiata pine usually resulted in the
strength properties being achieved but the stiffness
properties being well exceeded. As stiffness is
commonly is the key factor in design the structural
properties of pine were not then being fully utilised.
Secondarily the NZ Radiata Pine structural timber
resource was found to have an average stiffness of 8GPa.
Taking into account that NZ had an extensive history of
building houses with No 1Framing (MoE = 8GPa) it was
logical to take the Australia MGP system and extend it
lower. Thus two new machine stress grades (MSG)
based on MoE’s of 8 & 6GPa were developed.
Ultimately the final NZ MSG grades became MSG 15,
12 10, 8 & 6 (Table 1).
In the development of any set of structural grades, it is
important that there are enough grades to cover the
extremes of the current and future forest resources. It is
accepted however that in practice market and production
constraints will limit the sawmill to only producing three
or possibly four grades at any one time. The obvious
driver for the sawmiller/forest owner is to produce more
timber in the higher and more valuable grades, but if that
is not always possible then there is a lower but still
useable grade available. It is important to realise that
lower grades will not always result in proportional
increases in timber volumes in a structure. For instance
in a beam situation limited by stiffness an increase of
10% to the beam depth will compensate for a 25%
reduction in the Modulus of Elasticity
One study [4] took correctly graded No1 Framing from
six mills around NZ (Figure 3) and in conjunction with
the bending strength and stiffness data determined the
characteristic bending strength and stiffness values.
Mill C
Mill B
promotion of machine stress grading which actually
provides direct measure of stiffness. It was however
accepted at the time that the visual grading would still
play apart in NZ construction but would more and more
limited to larger sizes and the smaller producers.
This study provided further confirmation that Radiata
pine has a lower strength for given stiffness (Figure 2)
This information lead to the 1999 [1] study which looked
at revising the strength to stiffness relationships.
Mill A
Mill F
Mill E
Mill D
Figure 3: Location of study timber
Figures 4 and 5 show characteristic bending strength and
stiffness for the sample of correctly graded No 1Framing
150x50 timber. In terms of bending stiffness there was a
4GPa difference across the country with 5 of the 6 mills
achieving the No1 Framing grade value of 8GPa. In
terms of bending strength only two of the mills achieved
the No1 Framing grade target value of 17.7GPa.
150 x 50 Bending Stiffness
10
9.195
8
7.736
8.313
8.089
8.083
Target Stiffness 8.0 GPa
6
5.743
Key
4
25%
2
Ek
0
Mill A
Mill B
Mill C
Mill D
Mill E
50%
75%
Mill F
Confidence band
Bending Stiffness Ek, (GPa)
12
Figure 4: No 1Framing bending stiffness
150 x 50 Bending Strength
26
23.23
22
21.27
20
18
16
19.35
17.32
14.68
14
12
12.04
Target Strength 17.7 MPa
18.47
16.40
13.95
15.47
15.67
15.98
14.37
13.13
11.59
12.34
10
10.28
9.23
8
Key
25%
6
4
Rk(0.05)
2
0
Mill A
Mill B
Mill C
Mill D
Mill E
Mill F
50%
75%
Confidence band
Bending Strength Rk, (MPa)
24
Figure 5: No 1Framing bending strength
This trend of wide variations in bending stiffness within
a single visual grade further confirmed the widely held
belief that visual grading cannot reliably grade for
stiffness. The solution here was to continue with the
Stiffness to strength relationships
Traditionally the approach taken in setting the strength
properties of structural grades has been to carry out an
extensive strength testing program across the forest
resource over a range of sizes. The test data in
conjunction with the grade data is then analysed to
determine the strength values. The published strength
values can have a degree of conservatism built in them
over the test data. Usually it is only the foresters and
producers plus the researchers that are involved in this
process but ironically none of these parties actually use
these values, for the producers they are just a set of
performance targets to be achieved. It is the design
engineers that use these values and directly see the
impact in their designs.
Hence the approach taken in setting the new grade
stresses had three drivers.
1. What were the actual strength properties of the
forest resource as determined by test.
2. How low could the strength properties relative
to the stiffness values be set without
significantly influencing the design and
ultimately the volumes of timber required to
build houses. In timber design it is very
common to hear engineers taking about
stiffness limited design. The implication here is
that strength is being over achieved.
3. To make the in-mill quality assurance strength
testing less onerous.
NZS3604 New Zealand’s light timber framing code
currently sets the timber sizes needed for given spans
and loadings. Using NZ3604 as the design client a study
was undertaken where the strength properties were
lowered (keeping stiffness unchanged) until a point was
reached where strength was becoming a design
limitation. At this point stiffness was still the
predominant governing design factor but without the
excessive reserves in strength, this approach resulted in
the majority of member allowable spans remaining
unchanged. As an example the spans in NZS3604 were
based around the old No1 Framing grade had a bending
stiffness of 8GPa and bending strength of 17.7MPa,
Whereas the new MSG8 & VSG8 grades (Tables 1& 2)
have the same stiffness but a lower bending strength of
14MPa. This 3.7MPa reduction did not significantly
changes the span tables in NZS3604.
One of the downstream benefits that was quickly realised
was that with the lower strength target it became a lot
easier for the wood producers to satisfy the bending
strength verification target. In general on observing the
implementation of product Quality Assurance if the
acceptance targets are low enough that a producer
commonly gets a QA pass then the barrier limiting
widespread adoption of product QA with third party
auditing is significantly reduced.
Another issue that needed to be addressed was to link the
availability of the timber grades and sizes to the
designers. Without this link a grade size combination
can be easily selected by the designer that is not
produced or not readily available in close to the location
of the structure. This incorrect selection can hold up the
building consent process if the design needs to be
reworked.
For example in New Zealand;
• MSG15 will be very rare, if available at all.
• MSG12 availability will be limited in volume,
dimension and by region
• MSG10 tends to be used in timber trusses but
will be limited in volume, dimension and by
region
MSG8 has become the grade of choice for light
timber, and it is widely available around NZ
• MSG6 is not that common as many producers
use that grade for their re-manufactured
products.
• VSG10 will be virtually limited to Douglas fir
• VSG8 is more common in the wider sizes but
does require additional effort in terms of a
knowledge of forests, log sorting, cutting
patterns, with stricter limits on visual
characteristics to achieve the required
properties. A lot of VSG producers have now
switched to being MSG producers
This is ongoing educational process via industry
presentations, and one of one discussions.
•
Table 1: Characteristic stresses for machine graded timber NZS3603 A4
Species
Grade
Radiata Pine
& Douglas Fir
MSG 15
MSG 12
MSG 10
MSG 8
MSG 6
Moisture Content – Dry (m/c = 16%)
Bending
Compression
Tension
Strength
Strength
Strength
MPa
41.0
28.0
20.0
14.0
10.0
MPa
35.0
25.0
20.0
18.0
16.0
MPa
23.0
14.0
8.0
6.0
4.0
Bending
Stiffness
GPa
15.2
12.0
10.0
8.0
6.0
Lower bound
Bending
Stiffness
GPa
11.5
9.0
7.5
5.4
4.0
Table 2: Characteristic stresses for visually graded timber NZS3603 A4
Radiata pine &
Douglas Fir
Bending
Strength
VSG10
VSG8
No 1Framing
MPa
20.0
14.0
10.0
G8
No 1Framing
11.7
7.5
1. Moisture Content – Dry (m/c = 16%)
Compression
Tension
Strength
Strength
MPa
MPa
20.0
8.0
18.0
6.0
16.0
4.0
2. Moisture Content – Green (m/c = 25%)
12.0
4.0
11.0
3.0
Bending
Stiffness
GPa
10.0
8.0
6.0
Lower bound
Bending
Stiffness
GPa
6.7
5.4
4.0
6.5
4.8
4.4
3.2
3. NZS3622 PROPERTY
VERIFICATION
Visual grading history
Historically in New Zealand structural timber was only
visual graded primarily using features like knot size and
location, presence of pith, sloping grain etc.. Different
rules existed for the different grades and sizes. The
common visual grades were No 1Frame and No 2Frame
visual grades, the Engineering grade has all but ceased to
exist due lack of timber that satisfied the strict
requirement on knot size. As previously noted visual
grading has the ability to grade for strength but not
stiffness. The visual graders have to be trained and have
to achieve grading accuracy targets; however there was
no requirement for checking for the final graded strength
and stiffness properties.
Machine grading history
The early producers of machine grade timber used a set
of machine grade threshold developed for the ‘F’ grades
in NSW in 1974. The producers then applied a visual
override that was largely specific to the individual
producers. The different producers developed their own
in house methods to control the quality of the machine
graded timber. These methods did not always have a
feedback loop back to the machine stress grader to allow
adjustments to be made to the threshold settings.
In the early 2000’s a large timber producer was found to
be selling timber that did not have the claimed structural
properties. This issue was almost certainly not just
limited to this one company particularly as the majority
of timber sold in NZ was visually graded without any
property verification quality control.
It has long been recognised the importance that the end
users of structural timber must have confidence in the
timber products. Their design and structures rely on the
fact that timber used has the properties claimed for it, if
not the structures may not perform in service as
intended. If the timber industry could not provide this
confidence there was a real risk of market share decline.
Taking all this issues into account it became apparent
that New Zealand had to develop a property verification
method in the form of a NZ standard. The key features it
needed to have were:
• It must provide some form of guarantee of
structural properties.
• It must use output control not machine control. The
emphasis must on the quality of the final product
not the procedures used to produce the final
product. There must be flexibility in the grading
methods used but consistency in the property
verification.
• It must be easy to implement and manage in
sawmill situation.
• It must be acceptable for timber exports to
Australia.
• It must incorporate third party auditing.
•
•
There should some incentive for producers to enter
into a property verification scheme.
It needs to be applicable to both visual and machine
graded timber. The actual verification checks must
be the same.
It should be acknowledged that the wood processing
industry were initially wary of third party auditing but
when it became apparent that it was possible to
continually satisfy the requirements of NZS3622 without
disruption to production, third party auditing was
universally accepted and has become a significant
marketing benefit.
The initial approach was to look at the verification
method used Australia AS/NZS4490. This was rejected
as it did not have provision for third party auditing.
Accordingly it was decided to develop a new NZ
property verification standard (NZS3622), this standard
would be limited to structural timber only as other
structural timber products such as LVL and Glulam have
their own standards.
The approach taken in NZS3622 was;
• Adopt a target bending stress as being an
estimate of the property value determined with
75% confidence that would be exceeded by
95% of the product.
• Adopt a target mean stiffness as an estimate of
the mean value.
• Adopt a target 5th percentile stiffness as being
an estimate of the property value determined
with 75% confidence that would be exceeded
by 95% of the product.
For bending stiffness this resulted in a rolling 30 piece
average which is monitored to be above the target. In
practice the target has been set at 0.5GPa above the
assigned characteristic grade value. The lowest recorded
stiffness value in the previous 30 test results is taken as
the 5th value which must be above the assigned lower
bound grade value.
For bending strength producers had the option of testing
timber to destruction to determine a 5th percentile or
proof loading to the characteristic grade stress. Most
producers favoured the proof loading approach as less
timber was broken. The acceptance criteria is that no
more than 1 piece in a sample of 30 could fail the proof
load test and none shall fail at less than 90% of the
characteristic bending strength.
NZS3622 also sets out
• Requirements around the initial evaluation
• Requirements for the audit organizations
• Sampling procedures
• The information needed to be displayed on the
timber
• Product release procedures
If a company chose not to verify their timber due to the
fact that they were either a very small producer or
producing a single batch of timber then an unverified
option existed. This being that the design properties of
the unverified grade where reduced to level whereby
there was confidence that the grade properties were still
going to be achieved. This grade is No 1 Framing (Table
2).
Since the introduction of NZS3622 in 2004:
1. NZS3622 as has been recognised as acceptable
solution for timber being imported into Australia.
2. The wood processing industry has developed a
standard operating procedure (SOP) that deals with
the issues around the implementation of NZS3622.
This group comprise of the auditors, industry
representatives and researchers. To date this has
been very successful in ensuring everybody has the
same performance targets and code interpretation.
Ultimately the requirements of the SOP will be
included in a revision of NZS3622
3. Under NZS3622 the industry has now tested
several hundred thousand pieces of timber; many
companies have linked this data back to log and
forest to enhance their financial returns.
4. Two new auditing companies have been established
and two others have broadened their scope to
include NZS3622.
5. Over 90% of structural timber is now third party
verified compared to 0% pre 2004.
4.
In order to continue to promote the uptake of machine
stress grading over visual grading it was seen that
•
A new low cost machine stress grader was
needed.
•
Higher production speeds were important.
•
A more flexible machine would be beneficial.
•
The new grader must offer a financial benefit
over both visual grading and the traditional
machine stress graders.
A-Grader
Scion in partnership with Falcon Engineering developed
a machine stress grader, the A-Grader which measures
the stiffness of timber via acoustic waves.
The
traditional machine stress grader relied on the timber
being passed linearly through the machine grader, the AGrader however graded the timber when it was travelling
laterally in a lug chain. The advantage of this approach
was that the timber was travelling slower for the same
throughput and lug chains existed in both green and dry
mills. The most significant was that the A-Grader could
machine stress grade both green and dry timber, rough
sawn and planed, a wider range of sizes, random width,
depth along with random lengths.
Its installed capital cost was less than new plank graders
with the installation costs being significantly lower than
a traditional linear grader.
Figure 6 shows a typical A-Grader installation
NEW ACOUSTIC MACHINE
GRADING TECHNOLOGY
Scion from the 1980,s onwards has long been pushing
the benefits of machine stress grading over visual
grading as the optimum form of structural grading. It
has long been noted that visual grading [1] does not
directly measure stiffness – generally the most important
characteristic in design. It is the stiffness properties that
control the allowable spans for the majority of light
timber framed structures covered by NZS3604
At the same time the grade recoveries in visual grading
had declined as evidenced by the fact that the highest
visual grade (Engineering Grade) had all but disappeared
for the structural market.
In 2000 there were approximately 7 machine stress
graders operating in NZ these were a mix Metriguard’s
Eldeco Darts and Plessey Computermatics.
Most
companies considering installing a machine stress
grading were attracted to the Computermatics due their
second-hand availability from Australia and Europe. A
second-hand machine could be purchased and installed
for under $NZ100,000. The issue at the time with the
Computermatics was that the technology was originally
developed in the 1960/70’s with a solid state control
unit. The solid state control unit was generally reliable
but it used components that were no longer produced and
hence irreplaceable, mechanically replacement parts
were usually available from scraped machines.
Figure 6: A- Grader (cover removed)
Prior the development of the A-Grader Scion undertook
a machine grader comparison study [5] in which the
same batch of timber was machine graded by a range of
traditional plank graders in sawmills and then using a
range of laboratory techniques. After grading the timber
was tested for its bending strength and stiffness in
accordance with AS/NZS4063:1992. The key outcome
of this study is best shown in Figure 6 which plots the
30%
380
25%
360
20%
340
15%
320
10%
300
5%
280
0%
Value Recovery $/m
3
400
Value Recovery
Average Grade CoV%
value recovery and average coefficient (CoV%) of
bending stiffness for each of the grading operations.
Essentially as the CoV reduces the accuracy of grading
increasing and the value recovered increases (more
timber into the higher more valuable grades).
Average Grade CoV%
Figure 6: Value recovery vs grading machine
This outcome has since been realised by the operators of
acoustic grading machines.
Since the introduction of A-Grader the use of acoustic
machine stress grading technology has been widely
adopted in NZ where it is now estimated that over 50%
of the structural timber graded in NZ is done by acoustic
machine graders.
5.
1.
2.
3.
4.
5.
6.
7.
2012 UPDATE.
The number of machine stress graders in use in NZ
is now approximately 40 up from 7 in 2000. With
the majority of timber now sold as machine stress
graded
Well over half the machine stress graders in NZ
production are Acoustic graders.
All the companies producing MSG timber are part
of the NZS3622 property verification scheme.
NZS3622 is now an acceptable solution under the
Australian machine grading standards. This has
resulted in NZ being able to export structural
timber (verified in NZ) to Australia.
The majority of the visual grading processors are
part of the NZS3622 property verification scheme.
The exception generally being those small
producers who could neither afford to enter a
property verification scheme or have chosen not to
but are happy to sell their products as unverified No
1Framing grade.
The wood processors have endorsed the NZS3622
verification system with its wide spread adoption
and have quickly realised the benefit of third party
auditing. In doing so they have gained a great deal
of knowledge linking log supplies to product
properties.
The wood processors have jointly developed
standard operating procedures around the
implementation of NZS3622.
8.
The most common grade sold in NZ is MSG8
which is a natural fit with the forest resource and
the house construction.
9. The house building standard NZS3604 has been
modified to incorporate the new verified and the
unverified grade, there has been negligible impact
on volumes of timber used in houses.
6.
CONCLUSIONS
This significant transformation has taken place by:
• Ensuring that the science was connected to industry
application.
• A high degree of engagement and support from the
wood processors, the regulatory bodies and the end
users.
• The matching of structural properties of the forest
resource to the design requirements.
• The provision of a better grading technology.
It is suggested that without addressing all these issues
together this change would not have taken place as
quickly and would not have been so universally
accepted.
In summary the structural timber industry is now in a
very strong and united position with the ability to
produce verified structural timber making best use of the
forest resource. The reputation of NZ graded Radiata
pine has been considerably enhanced and the future will
be much more assured.
ACKNOWLEDGEMENTS
The author wisher to acknowledge all parties involved in
making this transformation to the structural timber
industry. Namely:
Fellow researchers at Scion, BRANZ, Standards New
Zealand, Falcon Engineering and most importantly the
timber industry itself.
REFERENCES.
1.
Gaunt, D. J., Roper, J., Davy B., 1999,
Performance Grading Of New Zealand Pine and
The Development Of The ‘E-Grader’,
Proceedings of the Timber Industry Federations
AGM, November 1999.
2. Collins M, Gaunt D, Roper J, 2000, MGP8 –
Can it be substituted for No 1Framing in
NZS3604?, Wood Processing Newsletter, Issue
28, December 2000.
3. Walford, G.B, 1996: An In-Grade Evaluation
of Machine-Graded New Zealand Radiata Pine.
Proceedings of the International Wood
Engineering Conference, New Orleans, USA,
Vol. 2, pp 287-292.
4. Strength and stiffness of visually graded radiata
pine in large sizes, Revised September 1997.
Value Recovery Report
5. Machine Stress Grading Technology Evaluation
Part 1: Machine Evaluation A Multi-Client
Report: Forest Research.
6. AS/NZS AS 4063:1992: Timber - Stress graded In-grade strength and stiffness evaluation,
Standards Australia/Standards New Zealand.
7. AS/NZS AS 4490:1997; Timber - Stress graded –
Procedures for monitoring structural properties.
Standards Australia/Standards New Zealand.
8. NZS 3631:1988. New Zealand National Timber
Grading Rules, Standards Association of New
Zealand.
9. NZS 3603:1993 A4. - Code of practice for
Timber Design, Standards Association of New
Zealand,
10. AS1720-1997, Part 1. Timber Engineering Code,
Standards Association Of Australia
11. NZS3622:2004
Verification
of
Timber
Properties, Standards New Zealand.