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Question

Hi, im in a BAL40 zone. I want to build a veranda, and am unable to work out if I am able to use timber or not in the construction. I want to use Blackbutt or Ironbark posts and beams, which will be exposed timber. I will then use f17 vicash for the rafters and battens, plus cover the veranda with metal sheet roofing. Does the standards allow me to use these timbers?

WoodSolutions Answer +

Bushfire regulations look to the roof elements of verandahs and similar attached structures. In a BAL-40 zone if the verandah is separated from the roof space of the main structure by a bushfire-compliant wall that extends to the underside of a non-combustible roof covering, you just need to line the underside of the rafters with 6mm fibre-cement sheeting. The regulations outlined in the Australian Standard make no direct reference to supporting posts, but we recommend the use of bushfire-resisting timber. Blackbutt or ironbark would therefore be fine since both are classed as 'bushfire-resisting'. 

Question

How do you calculate the axial shortening for timber columns in high rise structures?

WoodSolutions Answer +

Typically the issue is not the column shortening, but the yield under compression perpendicular to the grain of floors/plates, combined with the shrinkage of the same elements. So, the more “horizontal” grain in a given design, the higher the shortening.It is very much related to a given design and loading, so it's difficult to give a generic answer. For more detail on this topic contact Paolo Lavisci here: Paolo.Lavisci@woodsolutions.com.au.

Question

By comparing with the suppliers products lists and SA HB 1.8-2013 appendix A, I found that glulam and LVL cross section size could be different. Under this circumstance, if there are any rules to make standard sizes. Furthermore, when we design timber structures by using these two materials, do we need to decided which supplier will be choose firstly, then started design process, or we can design the structure first, then ask the supplier to provided the material size which we decided to use? Thanks.

WoodSolutions Answer +

LVL dimensions and properties are not standardised. For example, Tilling's SmartLVL comes in thickesses of 35mm, 42mm and 58mm, whereas Carter Holt Harvey produces thicknesses of 35mm, 45mm and 63mm. Both produce a limited range of 75mm material. They also have different characteristic strength properties, so yes, when designing in LVL it is necessary to select a product at the start of the design process and nominate that product in the specification and on working drawings. However, Australian-produced glulam is made with a standardised range of properties and you will find more information on the net here: http://www.lamtim.com.au/gltaa.pdf

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