Log Quality, Conversion and Grading

Log quality is a function of size (diameter, length) shape (straightness, ovality, taper), and other external (branching) and internal (wood properties) features which can affect the suitability for a particular end use.

Adaptability of New Zealand pine (which comprises the most part of New Zealand's plantation forestry) to varying site and management regimes results in the production of a range of log types. Grades based on quality characteristics are used in New Zealand to allow buyers to specify the preferred quality. The key to the appropriate use of these logs is to recognise associated quality variations and to match them to the intended process and product.

The wood of New Zealand pine has medium density, even texture, and average shrinkage for softwoods. The logs yield the full range of lumber grades from longlength clearwood to industrial grades. The strongest, most stable wood for structural uses is derived from the outer region of the log, while lumber from the juvenile zone is suited to packaging and similar products.

Contrary to popular belief, the wide growth rings typical of managed plantations of New Zealand pine are not a reflection of poor wood quality. Correctly graded, New Zealand pine conforms to grade requirements for structural lumber worldwide.

Reference:

NZ Pine User Guide, courtesy of NZ Pine Manufacturers Association

Log Quality, Conversion and Grading

Case study

Processing Factory for Kanuka Engineered Wood Products Ltd

Structural Concepts Ltd and Kanuka Engineered Wood Products Ltd

Key Features

At 60 metres wide with no internal supports, and made primarily from laminated timber, the building is a feat of innovative engineering designed to showcase the same product manufactured within.
Integral to the design are the large roof trusses which make up the majority of the 300 cubic metres of Pinus Radiata laminated wood used in the building.
For added strength, the bottom chords of the trusses have been laminated with Douglas Fir.
One of the many benefits of trusses is the ability to cover the required building width using smaller pieces of timber.

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Case study

Nelson Pine Industries Ltd warehouse

West + Tritt Architects

Key Features

Nelson Pine Industries Ltd manufacture laminated veneer lumber (LVL) from locally grown Pinus radiata, so it was natural this material was used to construct their new warehouse.
The brief required a storage facility of 16,500 m2 to be designed as a showpiece for the use and functionality of LVL.
The overall dimensions of the building are 128 x 64 m, with an eave of 10 m and an apex of 14 m.
Double 64 m portal frames at 8 m centres span the long direction.
The apex of each frame is supported on a longitudinal beam spanning 16 m between posts.
All portals, beams, posts, purlins, girts and diagonal wall bracing are made up from the raw LVL billets manufactured on site.
The 400 x 45 mm purlins and girts were cut from the basic billet size while the rafters and legs were built up from the basic billet using glued and nailed splices.
The portal knee and apex gussets have been nail fixed only to give increased ductility.

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Case study

Carter Holt Harvey Marsden Point Factory

Timberbuilt Pty Ltd

Key Features

Carter Holt Harvey utilised its laminated veneer lumber (LVL) product in the construction of its new Marsden Point manufacturing plant.
Covering more than 2 ha, the building houses the assembly, pressing, finishing and despatch functions for LVL manufacture.
The structural system involves rafters extending across the full 96 m width supported at four points, creating three 32 m spans.
The outer columns are rigidly connected to the rafters to form portal frames while the inner columns act as simple props.
The rafters are either 1,200 or 1,265 mm deep LVL I-sections spliced at six points.
Outer columns are the same dimension but taper down to 800 mm at their base.
Internal columns are box sections fabricated from 300 mm x 45 mm LVL.
Composite plywood and LVL I-beam purlins span 11 m between rafters.
In total, 620 m3 of LVL, 50 m3 of structural plywood and 15 m3 of sawn and dressed timber were used in the construction.
This project demonstrates that large-scale industrial buildings can be built successfully with timber.