I have to find the compressive strength of CLT samples that have a rectangular cross section - I know that this is not the most ideal scenario, and a cube would have been better - but what are the ways of calculating the compressive strength? Assume a spherical area?
Aspect ratio of the test specimen have effect on the strength being measured. You might be aware of the concrete compressive strength in case of cube and cylinder. Similarly the core strength of concrete has relationship with the aspect ratio. We need similar findings on large scale data base to correlate strength of wooden samples having cuboid to cube
The compression strength of CLT when loaded perpendicular to the grain is indeed highly dependent on the loading situation. The strength values, as evaluated according to the EC5 definition of compression strength, depends on the load arrangement. In addition, the recorded data shows that the shape of the stress versus deformation curve is also highly dependent on the loading situation. For the case of loading by a uniform pressure or uniform displacement the stress versus deformation curve shows the typical behavior of reaching a clear plateau value. Following this, at very large compression strain, intensification occurs. Thus, for this mode of loading, it seems reasonable to assume that for a design situation, the excessive deformation is the limiting factor. The post-plateau case there is a large safety margin built into any design criterion based on maximum deformation. For the other cases of loading, i.e. by applying the load on only parts of the specimen’s surface, the situation is different. For the “worst case scenario” - a line load close to the edge and parallel to the surface grain direction - strength values are lower and, above all. This is mainly due to the lack of interaction between the individual boards of the CLT. For cases were a board with small width is situated at the edge, the failure is very local, and also much more brittle. The failure mechanism in this case is that of rolling shear in the board closest to the edge. Since the boards are not structurally glued at their edges, the transverse deformation is not prevented. From this introduction and considering all influenced parameters, the cylindrical specimen is good for isotropic materials which is not matched with timber properties, therefore for a rectangular section you,d better use the cubic sample to measure the strength of timber elements.
Wooden specimen need to be check for parallel to the grain as well as perpendicular to the grain. Rate of loading also influence the compressive strength of specimen. One has to correlate actual condition of loading with specimen tested in laboratory to arrive at reasonable conclusion.
Janeshka Goonewardena I recommande that you take a look at this book
ENGINEERING MECHANICS OF COMPOSITE MATERIALS
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