Historic timber bridges reveal lessons, and questions about the reliability of radiata
Authors: Chapman, John
Abstract: The paper looks at 3 recent studies to discuss the use of pinus radiata for industrial and
commercial construction. The first study reports on two historic bridges and the lessons they reveal for
designers of modern timber structures. The stresses in the bridge members and their significance for
future maintenance works are explained.
In the 2nd project, a 5th year architecture student compared a conventional glulam bridge with an
equivalent bridge, which utilises historic bridge structural and jointing systems. The paper reports how
the historic bridge structure with radiata pole elements proved to be considerably more economic in
the amount of timber used and in material cost than the conventional glulam bridge.
The historic timber bridges, built in New Zealand for road and rail, were made of Australian hardwoods.
When applying the relevant New Zealand code, ‘Timber Structures Standard, NZS3603:1993’, pinus
radiata poles appear to have physical properties which approach those of Australian hardwoods, such
as Jarrah. However, in the 3rd study, questions about the reliability of the strength of the current crop of
pinus radiata poles arise when joints made from radiata poles, and designed similarly to successful
joints in historic bridges, fail at unexpectedly low loadings.
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