(bouncy futuristic music)
-: With global climate change,
the intensity and the frequency of severe climate increases.
At the same time, over 50% of US population
is concentrated in the coastal areas,
where the properties and structure values are high,
and the population growth rate
outpaces the national average.
Since most of the construction is wood based,
hurricanes and other natural disasters
are major threats to our homes and business.
As the picture showing, the house were damaged by tornado.
In the two pictures on the right side
show the shear value of columns and beams.
Shear value is one of the reasons
why wooden structure is so vulnerable in extreme weather.
Knots are inevitable part of wood material.
Size and quantities are stated in ASTM standard
when the lot graded.
People always regard the knots as a kind of defect,
which will affect the mechanical properties of wood.
What I did is to figure out what the knots
actually affect on longitudinal shear strength.
I took Southern yellow pine as a test material.
There are four variable parameters included.
The decay and the sound knot,
the shear plan perpendicular
and parallel to the wood grain.
Totally, 240 samples were tested.
By analyzing the data, I have three hypotheses.
First, live knots can enhance shear strength,
while the decay knots will decrease the shear strength.
Second, shear strengths will be larger
when the shear plane parallel
rather than perpendicular to the wood grain.
Third, comparing to horizon line,
the smaller the knot's angle,
the larger the shear strength will be.
When we get this result,
it can be a reference of revising our standard.
Besides that, some suggestions can be given
to sawmill to help them save amounts of money.
While this is just a small and fundamental research
of wooden structures,
more tests about how the knots
affect other mechanical properties
should be carried out in the future.
(bouncy futuristic music)