Similarly, I decided to buy our current house on the basis of walking in the front door and straight out the back door, until I saw the dam. I didn’t need to see the tiles in the bathroom or the size of the bedrooms.
I didn’t even know we had a pizza oven! Done deal!
By contrast, as soon as I am forced to make a relatively trivial choice, I am paralysed by indecision. Given a choice between mobile contracts, I inevitably waste ages working out which is best. I avoid flying Jetstar just because they offer so many choices in their online bookings. It’s “˜paralysis by analysis’.
To help me as much as you, I have had my engineer research the timber properties of available Laminated Veneer Lumber’s (LVL) to be used as beams. At least we can get some clarity on that.
I should start out by saying that the following analysis is only intended to help differentiate between LVL’s when used as beams, rafters, lintels, floor joists and the like. Use in trusses is another question altogether.
There are a stack of engineering properties of any timber. What is most important? What governs the design? It turns out that in the vast bulk of cases, that beam deflection or bounce is what limits the design.
It is very rare that the span of a beam is limited by the breaking or buckling of the timber.
Let us focus in on the one material property that governs deflection and bounce – material stiffness. The “˜original’ LVL’s available in Australia had a material stiffness of 13.2GPa and Wesbeam, Carter Holt Harvey and Nelson Pine currently do this middle-of-the-road stiffness LVL.
The “˜plus’ versions of LVL are only six per cent stiffer than “˜original’. With beam deflection limiting this translates to only about a 2 per cent improvement in spanning ability, this higher grade is effectively a marketing exercise.
Tilling’s highest grade gives a 10 to 14 per cent maximum span improvement compared with “˜original’. Conversely, Nelson Pine’s LVL11 has a 5 to 6 per cent reduction in maximum spans compared with “˜original’.
Bending strength and shear strength can limit beam span for short, highly loaded the beam. However, to reiterate, almost all domestic beam type members are governed by deflection.
It might be easy to be dazzled by a marketing brochure that quotes engineering properties. Hopefully the above analysis helps equip you to decide on value for money for LVLs.
Meanwhile, I will continue to struggle on the domestic front when faced with endless choice, what laptop should I buy? Which olive oil? I have minor notoriety within my family by choosing, fitting and paying for my wedding suit in fifteen minutes flat simply because the hire place cleverly offered me only two choices.
Come to think of it, I suspect that I would still be single except that my choice of wife was, effectively, made by her!
Paul Davis is an independent structural engineer managing his own consulting firm Project X Solutions Pty Ltd. The views in this column are Paul’s and do not reflect the opinions of TimberTrader News.
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