WEBVTT

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(bouncy futuristic music)

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<v ->With global climate change,</v>

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the intensity and the frequency of severe climate increases.

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At the same time, over 50% of US population

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is concentrated in the coastal areas,

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where the properties and structure values are high,

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and the population growth rate

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outpaces the national average.

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Since most of the construction is wood based,

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hurricanes and other natural disasters

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are major threats to our homes and business.

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As the picture showing, the house were damaged by tornado.

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In the two pictures on the right side

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show the shear value of columns and beams.

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Shear value is one of the reasons

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why wooden structure is so vulnerable in extreme weather.

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Knots are inevitable part of wood material.

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Size and quantities are stated in ASTM standard

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when the lot graded.

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People always regard the knots as a kind of defect,

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which will affect the mechanical properties of wood.

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What I did is to figure out what the knots

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actually affect on longitudinal shear strength.

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I took Southern yellow pine as a test material.

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There are four variable parameters included.

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The decay and the sound knot,

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the shear plan perpendicular

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and parallel to the wood grain.

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Totally, 240 samples were tested.

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By analyzing the data, I have three hypotheses.

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First, live knots can enhance shear strength,

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while the decay knots will decrease the shear strength.

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Second, shear strengths will be larger

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when the shear plane parallel

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rather than perpendicular to the wood grain.

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Third, comparing to horizon line,

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the smaller the knot's angle,

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the larger the shear strength will be.

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When we get this result,

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it can be a reference of revising our standard.

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Besides that, some suggestions can be given

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to sawmill to help them save amounts of money.

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While this is just a small and fundamental research

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of wooden structures,

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more tests about how the knots

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affect other mechanical properties

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should be carried out in the future.

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(bouncy futuristic music)