It is known that apparent mechanical performance improve on partial compression perpendicular to the grain. The equation in the construction standard follows the assumption that the surface deformation at additional area is exponential shape. However the factor to determine its shape has not been investigated.
In this research the influence of supporting condition was studied. It was suggested by FEM analysis that the factor is different among them and was confirmed by the experiments. Consequently, three different factors were proposed instead of 1.5/Zo (height of specimen) in current standard, 2.5/Zo for normal, 3/Zo for triangle and 5.5/Zo for double triangle.
