Many procedures have been used to analyze the wood behavior under a uniaxial stress field and determined the elastic constants of wood using uniaxial compression tests. On the other hand, the wood behavior when it is subjected to a three-dimensional stress field is unknown. Using confined compression tests this stress field can simulate and, consequently, it is possible to evaluate the wood's constants and their relationship. The specimen consisted of four-inch (about 10 cm) solid redwood cubes with different fiber orientation and physical properties.

It was supposed that shear strain did not interact with normal strain and did not occur in orthogonal directions. The stress-strain relations were given by:

It should be noted that there are a series of 6 equations and 12 unknowns. To solve this problem is used a set of three tests with three different test orientations, each one under 90° rotation.

In order to check these results with the theoretical values, it is necessary to transform the angles measured on the surface of the specimen to Euler's angles and apply the correct coordinate transformation tensor.

In this way, the goal of this paper is to analyze the results of confined compression test in redwood and then comparing them with uniaxial compression test. The current data may be considered to agree with the published values, except for the tangential directions. Theses values exhibit the effects of the boundary condition, or better, the effects of the friction.