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Question

I am trying to find a design guide or manual for the design and specification of nail laminated timber including:
- reduction factors relating to lamination
- maximum spacing of nails etc.
Do you have any resources that focus on nail lamination?

Woodsolutions Answer +

If you have access to Australian Standards nail lamination is covered in Section 2.4.5 of AS 1720.1, Timber structures, Part 1: Design Methods. Section 2.4.5 is titled Strength sharing between parallel members. The calculation of the modification factor for strength sharing, k9, is given as equation 2.4.5.3. For nail-laminated members AS 1684.2 Residential timber-framed construction assumes nmem = 1.0 and ncom = number of combined sections in calculating k9. Or to keep it simple just refer to AS 1684.2, Section 2.3 where the recommended nail pattern is shown.

Question

I have to install an exposed "eaves beam" under a 900mm roof overhang (some protection afforded) in a coastal area (SA). The Engineer has specified 240x45 F17.
I would prefer not to "clad' the beam but leave exposed - although I would be painting it in a suitable white paint.There are several spans; the maximum is 4m. For a continuous span construction i have spans of 6.6m, 7.5m and 9m. The beams are supported on hardwood posts (F17) - I still have to decide on a suitable connection?
I don't like the idea of several short hardwood timber spans joined over the posts, so i considered glulams ands lvl's. Unfortunately my research has left me a little confused. What would you suggest as a suitable exposed, but painted eaves beam?

Woodsolutions Answer +

Glulam is available in F17 grade but, if made from radiata pine, would have to be preservative treated to AS 1604 Part 5 if it is going to be in the weather. Note that AS 1604.5 requires any surfaces exposed after treatment, by cutting to length, notching or machining, to have a wood preservative applied. This is to restore the protective envelope. Alternatively it might be possible to source glulam made from a naturally durable timber. On the other hand if it is possible to extend the eaves sufficiently beyond the eaves beam so that it is protected from rain, durability is not important. Regarding the connection of beams to posts, the most positive method is to use a proprietary connector bracket, eg. one of the Simpson Strongtie stainless steel post caps.

Question

I'm designing a floating staircase and I'm after some advice on what timber to use for the treads. The design is such that the timber will be constructed like a sleeve to fit over the steel structure of the treads. So the timber needs to be durable of course. We're after a more pale timber rather than a rich deep colour. An Australian species would be preferable. And something cost effective would also be desirable. And lastly it would need to be reasonably readily available - although I would be happy to provide plenty of leeway to order it.

Can you please suggest any timbers that you think would fit this bill?

Woodsolutions Answer +

Most of our Australian hardwoods tend towards the darker colours. Tasmanian oak/Vic ash is in the lighter colour range, but not as hard as some timbers. If you are designing a commercial building we suggest a harder species, perhaps spotted gum. The colour varies somewhat, but presumably you need a fairly small quantity so you might be able to persuade a supplier to pick out the lighter pieces for your job. If the treads are to be a U-shape make sure they don’t fit tightly where the front and back edges wrap around the steel, ie. leave a few millimetres between timber and steel in case of shrinkage. Presumably the treads will be fixed by screwing from underneath. It helps if the back row of screws can be fitted in slotted or oversize holes, while the screws in the front row are fitted tight to keep a constant line. The timber must be kiln-dried, but there may still be slight shrinkage with changes in the seasons and/or prolonged exposure to air conditioning. Using screws  with washers in slightly oversize holes holds the treads down but allows for some minor sliding movement at the back of the tread.

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