by Kelsey Kress, Bryan Heinzelman, and Cody Corsetti
SRJC
Engineering 45
December 2009

• To see the effects of moisture on the strength of the wood, by soaking four different types of wood for various amounts of time and then compressing them.

• All samples had the same starting dimensions of .75x3.5x5 in.
• The 4 types of wood used were:
– Douglas Fir
– Pine
– Redwood
– Red Oak

• The 4 samples included:
– one that had been oven dried(the control)
– one that had soaked for 2.5 hrs
– one that had soaked for a day
– one that had soaked for 10 days.

• Most widely used lumber in the framing of houses.
– Doug Fir is softwood, the type of wood that is easy to work with.
– It's the most plentiful softwood in North
America
– It is relatively inexpensive

• Douglas Fir has a superior strength-toweight ratio
– This ratio is the stress at failure relative to the density of the wood.
• Its specific gravity allows for great nail/plate holding ability.

• Douglas Fir has great dimensional stability.
– This is the ability of the wood to retain its shape when subjected to various types of temperature, moisture, pressure and other stresses.

• Used in high-value carpentry such as flooring, paneling, trim, and furniture.
– Finishes nicely with a coat of stain or varnish.
– After milling, it has little insect or decay resistances; as a result, it is generally used indoors.

• Used for siding, decking, trim, paneling, and many other applications where the finished product needs to be aesthetically pleasing.
– Has a reddish-brown color that darkens with age.
• Redwood is lightweight and easy to cut and nail/screw into

• Redwood resists shrinking, warping, splitting and insects, which allows it to be used in abusive environments.
• Its cell structure has thousands of air cavities, which gives it a superior insulating ability.
• Its lack of resin makes it partially resistant to fire.

• Used to make wine barrels, flooring, and cabinets; another type of wood that produces a nice-looking finished product
• It is close grained, heavy, and difficult to cut/penetrate.
• It is one of the best types of wood used in steam bending.
– Red oak is a hardwood and, as such, it has many more pores and capillaries than does softwood.
• Red Oak was the most expensive of all our woods, coming in at $2.30 a foot.

• Hardwood (e.g.
Red Oak)
• Softwood (e.g.
Doug Fir, Pine and
Redwood)

• We oven dried all 16 of our samples over night to ensure that all water content was removed.

• We then weighed all of them to determine the mass before soaking.

• The wet samples were soaked for logarithmic time periods (e.g. 2.4 hrs,
24 hrs, and 10 days).

• We ran a compression test on the dry, control sample; increments of compression length were recorded at every thousand pounds of added force.

• After soaking for the amount of specified time, we removed the wet samples from the water, recorded their mass after soaking, and then ran a compression test on them.
– Again, compression length was recorded at every thousand pounds of added force.

• We then plotted stress vs. strain curves for all four types of the samples to determine the modulus of elasticity, yield strength, and possible tensile strength of the respective woods.

• Water Content is (Mass H2O absorbed)/ (Final Mass)*100
• Here is data:
• Dry:
–
D.F.
– Pine
–
Rdwd
– Rdoak
• 2.4 Hr:
0
0
0
0
– D.F.
–
Pine
– Rdwd
– Rdoak
• 1 day:
–
D.F
– Pine
– Rdwd
–
Rdoak
• 10 day:
– D.F.
– Pine
–
Rdwd
– Rdoak
12.09%
26.35%
2.69%
13.70%
12.04%
25.97%
12.90%
11.25%
24.84%
40.12%
19.35%
22.64%

45.00%
40.00%
35.00%
30.00%
25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
0.001
Water Content Vs. Time
1000
Douglas Fir
Pine
Redw ood
Red Oak
Note: The 1-daysoak samples had to be re-dried and then re-soaked.
This could have led to incorrect measurements, which cause the unexpected dip in the graph.
0.01
0.1
1
Tim e (log hours)
10 100

• When testing the red oak, the tensile test machine was turning on and off.
This is a possible reason for the inaccurate data points that caused the jump in the graph.
Dry Samples (Elastic Region)
1600
1400
1200
1000
800
600
400
200
0
0 y = 17907x - 150.38 (Doug Fir) y = 34287x + 52.499 (Red Oak) y = 13265x - 78.868 (Redwood) y = 21797x + 118.28 (Pine)
Doug Fir
Pine
Red Oak
Redwood
Linear (Doug Fir)
Linear (Pine)
Linear (Red Oak)
Linear (Redwood)
0.02
0.04
Strain
0.06
0.08
0.1

Modulus of Elasticity in lbs/in 2 (Slope of Elastic Region)
Dry 2 Hrs 1 Day 10 Days
Doug Fir
Pine
Red Oak
Redwood
17907
21797
34287
13265
16402
4717.5
29680
13941
11974
7207.2
23424
6637.8
10369
4278
18820
12602
Yield Strength in lbs/in 2 (Top of Elastic Region)
Doug Fir
Pine
Red Oak
Redwood
Dry
1255.586
669.4337
941.1192
284.9003
2 Hrs
856.0813
278.9307
996.4791
461.2333
1 Day
857.0253
281.6441
963.768
341.6856
10 Days
855.1686
165.7614
757.1046
338.0967

40000
35000
30000
25000
20000
15000
10000
5000
0
0,001
Mod Of Elasticity vs. Soaking
Time
0,1 10 1000
Doug Fir
Pine
Redwood
Red Oak
1400
1200
1000
800
600
400
200
0
0,001
Yield Strength vs. Soaking
Time
0,1 10 1000
Doug Fir
Pine
Redwood
Red Oak
• As soaking time increased, both the modulus of elasticity and yield strength generally declined as well.

• http://en.wikipedia.org/wiki/Lumber
• http://www.bearcreeklumber.com/species/douglasfir.html#more
• http://en.wikipedia.org/wiki/Strength_to_weight_ratio
• http://en.wikipedia.org/wiki/Specific_gravity
• http://composite.about.com/library/glossary/d/bldef-d1670.htm
• http://www.bearcreeklumber.com/species/ppine.html
• http://en.wikipedia.org/wiki/Pine#Uses
• http://www.softwood.org/PPWeb/EN/PPine_Char.htm
• http://www.bearcreaklumber.com/species/redwood.html
• http://en.wikpedia.org/wiki/Sequoia#Cultivation_and_uses
• http://en.wikipedia.org/wiki/Oak
• http://en.wikipedia.org/wiki/Hardwood
• http://plants.usda.gov/plantguide/pdf/cs_quru.pdf
• http://www.ces.purdue.edu/extmedia/FNR/FNR-288-W.pdf