Characteristic Perpendicular to Grain Bearing Test on Common Australian and Imported Timber Species PNA462-1718
The aim of this study was to re-establish the characteristic perpendicular to grain values for common timber species used in construction from Australia and overseas and to develop a method to calculate deformation due to perpendicular to the grain compression. This work’s purpose was to inform the design methodology used in the WoodSolutions Mid-rise Timber Building Structure Engineering guide, in calculating the axial shortening of lightweight mid-rise timber-framed buildings.
The research was successful in determining the characteristic perpendicular to grain bearing values for 15 separate timber species used in construction, including an investigation into different stress grades and locations of supply.
The research found that AS 1720.1 method of assigning characteristic design values for bearing perpendicular to grain by the strength group or by assigning a value for MGP stress graded timber did not match the values found from testing. The characteristic perpendicular to grain bearing values showed a closer relationship to the timber species’ density. Some of this variation could be assigned to the absence of direction within AS/NZS 4063.1 in calculating the characteristic values. The main issue being the lack of guidance on using the appropriate off-set method for determining the Fc,90 value.
The Modulus of Elasticity (MOE) Perpendicular to Grain was also determined from the test but the method used was not in direct accordance with AS/NZS 4063.1. During the process of testing perpendicular to grain bearing, an elastic load/deformation relationship was observed, and excellent indicative values of MoE perpendicular to grain could be found.
The new WoodSolutions guide on Mid-rise timber building structural design currently suggests that the MOE perpendicular to the grain is 1:25 relationship between MoE Parallel to the Grain and MoE Perpendicular to the Grain. However, the results from this research could not confirm this relationship, as the ratio was found to be highly variable from the limited testing program undertaken.
Pending further research being carried out, this research suggests a relationship between the Joint Group and average MoE Perpendicular to the Grain and has suggested amendments to the WoodSolutions guide be made to make better use of a more accurate average MoE Perpendicular to Grain values.