This article is the second in a series of engineered timber articles looking at the advantages and possibilities of mass timber construction, as well as its growing uptake in the industry. Part One explores why and how Australia’s poised to construct taller timber buildings, while this piece turns the focus on to LVL.
First developed in the early 1970’s, laminated veneer lumber (LVL) is a high-strength engineered timber product formed by assembling wood veneers (thin sheets of wood that are uniformly thick) and bonding them together with a ‘type A’ phenolic adhesive which provides a waterproof bond.
According to Alex Edwards, an associate at design and engineering consultancy firm Arup, a log is peeled to a 3mm thin laminate, dried and sorted by its physical properties, before being laminated back together in a way that maximises the strength of the output.
“The timber is produced in a continuous 1200 wide billet up to about 90mm thick. Sections that are deeper have to be made by some form of secondary fabrication process,” he explains.
Notably, the grains of each veneer are oriented in the same direction, with the veneering process improving the structural properties of LVL by randomising any defects; strength-reducing knots, for instance, are dispersed in various ‘locations’ as they are peeled into the veneer.
As a result, LVL is uniform and comparable in strength to solid timber, concrete and steel. It is also more durable and less prone to shrinking or warping, although its durability is, in part, based on the species of wood used.
Some major advantages of using LVL in construction are its relative low cost, and the fact that it can be manufactured to any length and desired shapes. This opens up the door to a myriad of design possibilities.
A unique example of the flexibility of the material is the Metropol Parasol in Seville, Spain. Designed by German architect Jurgen Mayer-Hermann and completed in 2011, it is one of the world’s largest timber buildings, and reaches a height of 28 metres, covering over 11,000sqm.
The floating structure, offering an archaeological museum, a farmers market, an elevated plaza, as well as multiple bars and restaurants underneath and inside the parasols, uses the highly load-bearing Finnforest Kero LVL which was manufactured in Finland. The timber was post-cured with an epoxy resin, and finished with a waterproof polyurethane spray coating.
Metropol Parasol by Jurgen Mayer-Hermann. Image: Nikkol Rot for Holcim
As the Metropol Parasol – and a variety of other projects including the NMIT Arts & Media Building in New Zealand – show, LVL is certainly not a new development, even in Australia. However, the local architecture and design industry has mostly employed the technology for domestic construction and smaller residential projects as floor joists, roof truss components and portal frames.
But, it might not stay that way for long.
LVL-ing up in Australia: Netball Central by Scott Carver
The properties of LVL make it suitable for public and commercial buildings, where it can be used as cross beams to support floors and ceilings, as well as beam structures to support the weight of rooflines. It can also be used in the construction of weight bearing walls.
The netball centre in Homebush, NSW, which is being constructed using 21 LVL portal frames, is a great example of Australia making headway in utilising the technology for larger scale projects.
Netball Central by Scott Carver
Known as Netball Central, the centre is the first in Australia to be solely dedicated to a female sport. It was designed by architects Scott Carver and Arup for Netball NSW (funded by the NSW Government, Office of Communities), and includes five standard netball courts and a show court, as well as administration offices and amenities.
The portal uses a joint design developed by the University of Auckland and the Structural Timber Innovation Company (STIC). Called ‘Quick Connect’, it consists of pre-fabricated and pre-installed LVL sleeves screwed to the main portal frame LVL members, and grooved to allow the insertion of threaded rods that are fastened to the receiving columns or rafters.
According to Claire Matheson, project architect at Scott Carver, this technique allows the timber frames to be bolted together at height, instead of having to screw them together. The process has greatly reduced construction time and costs, with the project to feature the largest Quick Connect portals with a span of 37 metres in the southern hemisphere.
Beauty, structure and cost collide
When asked why LVL was chosen as the main structural material for Netball Central, Matheson says simply that it is a different product not commonly used in Australia, and therefore the perfect fit for the nation’s first uniquely female sports centre.
“We felt that LVL provided a very different language to your standard sports facility withgrey or white circular, high-section steel structure. It has a very different feel and a warmth,” she explains.
“Cost and structural reasons were also considered, but our initial desire for the material was from a design perspective.”
Sustainability was another reason why the architects were so keen on LVL – it is a carbon sink for timber, and essentially a lower grade timber product (softwood) made to perform “structural gymnastics”.
The massive LVL structural sections (1200x280) have been woven into the very heart of Netball Central’s structural and aesthetic vocabulary. Unlike the smaller member sizes of steel portals, the LVL portals have become an essential element of the architectural language of the building.
The challenge of the new
To date, all 17 major portals for the standard court halls have been erected. However, the building process was not without its challenges, most of which derived from unfamiliarity of the product.
Fully understanding the material was therefore essential for the design team, with Matheson making two trips to New Zealand to research the benefits and challenges of LVL, how it is manufactured, and therefore how best to use it.
This due diligence process has proven beneficial and helped the team to detail the material appropriately, such as the orientation to reduce visibility of glue banding without increasing fabrication costs. It has also helped to identify handling challenges.
“LVL being manufactured from Radiata Pine is quite soft, and hence it needs to be handled differently from steel,” says Matheson.
Another challenge for the team was not having an existing standard to work with and towards. As a result, they had to formulate a new ‘language’ to communicate the appearance they wanted for the raw product, such as the number and frequency of knots, and splits within the face veneer itself.
“We had to ensure that we were getting a raw product with the specific feel we wanted and that was visually appealing for the fabricators. The main question for us was how we can provide a language and standard that would set a good benchmark for public buildings,” Matheson notes.
Netball Central under construction. Images courtesy of Scott Carver
Arup’s Alex Edwards adds that getting these nitty gritty details down pat from the outset is essential for a successful MTC building.
“They [architects and designers] need to be asking who is going to fabricate the project and what type of material they are going to use. There isn’t a lot of standardisation in the timber industry with different manufacturers producing different grades of material,” says Edwards.
“Likewise, different fabricators have different equipment that means that their preferred methods differ. Working with a fabricator early in the process is more important than other construction materials.”
Where to get the product?
The LVL portal frames for Netball Central were supplied by Nelson Pine and fabricated by HunterBond– both New Zealand companies. However, some Australian companies manufacture LVL as well.
Carter Holt Harvey's Hyspan LVL is manufactured from Radiata Pine veneers, and is more uniform than normal sawn timber because of its unique laminated construction. Ripped from 1.2 metre wide continuous lengths, Hyspan LVL can be width sawn or docked on-site to required size or lengths without affecting its design properties.
The product is certified by the Plywood Association of Australia, and can be used in various ways for residential projects, and as roof purlins, portal frames, box beams and ‘I’ beam flanges, wall girts, trusses and floor joists and bearers in commercial buildings.
It is also tested against AS/NZS 4357 Structural laminated veneer lumber, and suitable for working stress design in accordance with AS 1720.1 – 1988 SAA Timber structures code, Part 1: Design methods. Furthermore, Carter Holt Harvey ensures that the wood is legally sourced from managed forests, and offers FSC ‘Chain of Custody’ certifications upon request for green star points.
Hyne Timber's LVL E-Beam+ (F17) is another LVL product available in Australia. As an engineered timber alternative to F17 hardwood, it has a high strength to weight ratio, and is available in 35mm and 45mm thicknesses with depths from 90mm to 290mm.
Manufactured from plantation growth softwood by laminating pine veneer in a continuous assembly, the Hyne E-beam+ (F17) conforms to the requirements of AS/NZS 4357 – Structural Laminated Veneer Lumber, with the design loads used to determine member sizes in Hyne Design based on AS 1684.1 1999 – Residential Timber Framed Construction.
It is recommended for use as floor joists and bearers, lintels and verandah beams, and as structural roof members.