WOOD - Materials for Civil and Construction Engineers - page 417

Crushing Wedge split Shearing

FIGURE 10.12 Types of
failure in the compression-
parallel-to-grain test. (ASTM
D143). Reprinted with permis-
sion of ASTM.

Splitting Compression

and shearing

Brooming and
end-rolling

(in./in.) of the nominal specimen length per minute. The deformations are
recorded to 0.002 mm (0.0001 in.) over a gage length of not more than 150
mm (6 in.) for the large specimens or 50 mm (2 in.) for the small specimens.
Load-compression readings are recorded until well past the proportional
limit. The failures should occur in the center portion of the sample. If fail-
ures are occurring near the ends, the samples can be stacked such that the
ends dry relative to the middle. This will increase the strength of the ends
of the sample. The tests are then repeated on the conditional samples. The
type of failure can be classified as crushing, wedge split, shearing, splitting,
compression and shearing, and brooming and end rolling, as shown in
Figure 10.12.
The compression test perpendicular to the grain is performed on
specimens. The load is applied through
a metal bearing plate 50 mm (2 in.) in width, centered across the upper sur-
face of the specimen. The load is applied at a rate of 0.305 mm/min. (0.012
in./min.). Deflection readings are taken to the nearest 0.002 mm (0.0001 in.).
Load and deformation are measured until the deformation is 2.5 mm (0.1 in.).

50 * 50 * 150 mm 2 * 2 * 6 in.

1 2

10.10 Design Considerations

Measurement of wood properties in the lab does not reflect all the factors
which affect behavior of the material in engineering applications. For design
of wood structures, the strength properties given in Tables 10.3 and 10.4
must be adjusted for the following (National Design Specification ® for Wood
Construction, 2005, ASTM D2555):

Wet service

■

Temperature

■

Beam stability

■

Size

■