Tony Loughnan, LHT Engineering Solutions
Purlins butted between rafters to provide lateral restraint. Consider equilibrium moisture content which depends on the control of the internal space conditions. Typical economic conditions for indoor pool controlled atmosphere is 70%RH and 28ºC for which EMC approx 13%. But for uncontrolled conditions, for example a translucent covered pool you could get average 90%RH and 15ºC which would give EMC of about 21%. For this you need to interpolate between dry (16%) and green stresses (25%). (Ref. Timber Construction Manual, AITC). Consider heat effects. At 28ºC and 70%RH timber will lose about 7% of its strength.
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