WPS 234 Strength & Stiffness of SA pine

Problem in young timber resources

Low MOE

P. patula properties variation with rings from pith

As rings away from pith increases;

• Density increases

• MFA decreases

• MOE increases

MOE-top-bottom relationship

• MOE decreases as you move from bottom to top of tree.

MOE-compartment influence

• Comparments (specific group in plantation) has influence on MOE.

MOE & mean growth ring width relationship

• As mean growth ring width increases, MOE decreases.

Twist and restrictions

• The SANS limitation on twist is 10mm/m and on average and about 56% of all the boards was not suitable for structural grades due to twist.

• Twist can be reduced by good drying practices. Cutting boards shorter and fingerjointing them again can also reduce twist significantly.

Slenderness and stiffness

• Trees with increased slenderness require wood that’s higher in MOE and MOR in order to increase their resistance to buckling under its own weight or breakage due to excessive wind loads.

• Height played a smaller role compared to radius (ring width) in stiffness.

Increasing MOE of young pine wood

• Tree breeding

• Higher planting density