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Question

I am trying to find a technical specification data sheet or similar for installation of nail fixings into timber members. Specifically relating to the acceptable depth of the nail head into the member surface.

Woodsolutions Answer

Australian Standards for timber construction focus on nail length in the receiving member, rather than embedment of the nail head, since nail length in the 'second member', plus nail diameter, are the factors that govern the strength of the joint. If you are dealing with the nailing of a deck, nail heads should not be protruding above the surface of the decking as they will present a hazard to foot traffic. On the other hand they should not be over-driven to the extent that they are significantly below the surface of the decking as that creates a point for water to collect.

Answered on : 24 Jan 2022
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
Question

I work with the façade engineering team at WSP. We are working on a project where glulam timber members are being used as mullions and transoms in a large spanning glazing system. The timber framing provides the internal support for the glazing; the glass is structurally glazed to an aluminium frame which fixes to the timber. The timber is therefore entirely within the internal envelope of the building. Some details of the project for background information: • Location – Townsville. • Timber Species used – Victorian Ash, seasoned and formed into glulam profiles. • Typical mullion glulam member length/span – varies from 3.7m to 11.7m • Typical mullion glulam profile size – varies from 83mm x 200mm for smaller spans up to 166mm x 550mm for larger spans. We have been designing the connections of the timber members and have a query regarding shrinkage of the glulam beams. Thus far we have assumed the below in our assessment: • Delivery moisture content – 16%, as advised by the supplier • Equilibrium Moisture Content - 9%, assuming air conditioned building and as advised by Timber Research and Development Advisory Council Technical Note. • Shrinkage across small dimension of mullion profile (largest being 166mm) – tangential shrinkage of 0.31% / % MC, based on Typcial origination of glulam components and unit movement as per woodsolutions website and supplier data. • Shrinkage across longer dimension of mullion profile (largest being 550mm) – radial shrinkage of 0.2% / % MC, based on Typcial origination of glulam components and unit movement as per woodsolutions website and supplier data. However we have found varying values for longitudinal / axial shrinkage of the glulam members. Some sources state this is approximately 1/10 of radial shrinkage (which would be approximately 0.02% per % MC), other sources saying 1/100 of radial shrinkage to (which would be approximately 0.002% per % MC) and other sources say it is negligible. We note the wood solutions website does not provide values for longitudinal/axial shrinkage. Due to the length of the members on the project we want to ensure longitudinal/axial shrinkage is appropriately allowed for in connection. Therefore we ask if you can advise a suitable value (in % dimension change / % change in MC) for longitudinal / axial shrinkage in Victorian ash glulam members or otherwise provide a reputable reference for such data which we can use in our design? We look forward to your advice on this issue.

Woodsolutions Answer

Although producers such as Vicbeam advise that their timber “has been kiln dried to between 12-16%” (info from website) we feel that the upper limit is not likely to apply across the board and moisture content after manufacture is likely to be below 16%. The Glued Laminated Timber Association of Australia (GLTAA) website advises that “When Glulam is manufactured, the timber sourced for the purpose is typically kiln dried to about 10-14% in order to achieve an effective glue bond.” With regard to the figures quoted for longitudinal shrinkage of timber, in many cases they are rough estimates and generally apply to single sticks of timber rather than engineered products. Some published figures apply to the shrinkage timber undergoes in drying from ‘green’ to equilibrium, rather than reflecting the unit movement of timber in service, so care is needed in interpreting data. Further reducing the significance of longitudinal movement in glulam is the fact that one laminate which may have a greater tendency to shrink is restrained by other laminates which may have a lesser tendency. The inherent variability of individual pieces of timber is randomised to a degree when structural members are built up from a number of pieces of different grain orientation and density. If possible, it would be instructive to test the moisture content of your beams with a moisture meter, either in the supplier’s yard or upon delivery to site. An additional technical point is that the figures quoted on our website for radial and tangential unit movement refer to the radial and tangential directions relative to growth rings, not relative to the cross-section dimensions of a built-up member where the growth ring orientation of each laminate will be different, and randomised in the finished product. Finally, the only research we know of that looks at the movement characteristics of glulam undergoing sorption and desorption can be found on the net here: https://www.researchgate.net/publication/331320365_Moisture_and_temperature_induced_swellingshrinkage_of_softwood_and_hardwood_Glulam_and_LVL_An_experimental_study - refer to Figure 11c where strain diagrams are shown for Tasmanian oak glulam (aka Vic ash) under two different temperature regimes. The conclusion was that “the Coefficient of Moisture Contraction (CMC) in the longitudinal direction of glulam and LVL beams was found to be an order of magnitude smaller than in the transverse direction.”

Answered on : 02 Dec 2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
Question

The proposed windows and doors will be directly exposed to the North and South. The seals are to passive house standards. The doors are high 3.1m. Including 3 panel 'stackers'. In triple glaze format. Which of the following timbers would you consider will have the greatest longevity? Black Butt, Vic Ash or Manilkara? If there is better one what is it?

Woodsolutions Answer

We assume the windows and doors will be rained upon, with no shelter from verandahs or canopies. This will require a durable timber that can stand up to the weather. In addition, the doors will need a strong timber with good screw-holding properties since triple-glazed 3.1m high doors will be very heavy. There are several species of Manilkara. Assuming it’s the South American species Manilkara bidentata which is marketed in Australia as ‘Pacific jarrah’, this is an exceptionally hard, heavy and strong timber, according to CSIRO data. It is rated Durability Class 1, even in ground contact, and would be suitable for doors and windows when seasoned to a moisture content around 12%. Vic ash is not naturally durable but can be preservative-treated to H3 level. It is then marketed as ‘Iron Ash’. Blackbutt is rated Durability Class 2 in ground contact. To sum up, Manilkara is the strongest and most durable of the three you mention, but also the heaviest. If weight will be a problem, particularly where the doors are concerned, blackbutt or Iron Ash may be the better choice since they have adequate durability and are lighter in weight. Perhaps the weight of the doors in each of the three species could be calculated and a decision made on that basis. Other suitable timbers include merbau, ironbark, spotted gum, jarrah etc. We assume you will specify a protective coating to the external surfaces, preferably a paint system.

Answered on : 16 Nov 2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
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