CE330L Student Lab Manual
Wood Compressive Strength
Introduction
This manual section outlines the steps necessary to perform the Wood Compressive Strength lab
experiment. This test, generally following procedures in ASTM D 143 “Standard Methods of
Testing Small Clear Specimens of Timber”, studies the compressive strength of a wood sample
having the load applied (1) parallel to the grain and (2) perpendicular to the grain. The purpose
of the lab is to determine some of the mechanical properties of various species of wood. For the
purpose of this lab, the Modulus of Elasticity, E, is to be found. Using the Instron load frame, a
sample of wood will be compressed at a specified rate while load and strain measurements are
recorded using a computer-based data acquisition system.
Relevant Equations and Information
PL
AE where
Δ - Deflection (inch)
P - Load (kip)
A - Cross-section area (inch2)
E - Modulus of Elasticity (ksi)
The following information will be collected:
Length between supports, L (inch)
Width, b, and Depth, h, of wood sample (inch)
Type of sample used (i.e. white pine, yellow pine, etc.)
Force applied, P (kip)
Strain, (inch / inch)
The following information will be calculated using the above collected data:
Cross-sectional area, A (in2)
A b*h
Deflection, Δ (in.)
Strain * L
Modulus of Elasticity, E (psi)
E
PL
A
Department of Civil Engineering, Southern Illinois University Edwardsville
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2/5/2010
Wood Compressive Strength
CE330L Student Lab Manual
Materials and Equipment
Verify the following equipment has been setup and materials are present:
 Wood specimen (2), each approximately 6 inch x 1½ inch x 1½ inch
 one having its grain aligned parallel to the force path
 one having its grain aligned perpendicular to the force path
 Linear scale
 Instron test machine (preset for this experiment), including non-contact (video)
extensometer
 Computer with data acquisition software
 Digital camera
Safety Considerations
This experiment involves working with a powered load frame capable of producing a
force of over 60 kip. Always be sure to keep clear of the moving parts when the machine
is operating. Keep the guards in place while machine is operating. When installing or
removing the grips turn off the main power switch.
Always wear safety glasses around this machine when it is operating.
Procedure
The initial set up of the Instron machine and computer will be done prior to the lab. Each group
will conduct the experiment. The compressive load will be continually increased until after the
strain data recorded has passed the proportional limit. It is the job of each group to conduct this
experiment on their own with appropriate supervision.
1. Choose a sample that has appropriate grain features, free of cracks, checks, splits and no
knots larger than 1/8 inch in diameter.
2. For this experiment, be sure the grain runs parallel to the direction of loading. Measure the
height, width, and length of the specimen. Determine the species of sample. Record this
data.
3. Mark the two strain targets 4 inches center-to-center aligned vertically on the centerline of
one of the specimen faces,
4. Place the sample in the center of the loading frame so that the load may be evenly applied
to the specimen.
5. While watching the video extensometer’s image, carefully align the specimen so the strain
target marks are recognized by the video software (indicated by a small red circle around
each target mark) and in the center of the extensometer’s horizontal view.
6. Tare the initial strain recorded. When entering information prompted by the data
acquisition software, you should be sure to include a complete description of the test
conditions, including:
Department of Civil Engineering, Southern Illinois University Edwardsville 2/5/2010
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Wood Compressive Strength
CE330L Student Lab Manual
a. lab experiment title,
b. type of specimen,
c. load-grain alignment,
d. length, heath and width, etc., so that when you work on the lab report, you
will have that information available to you. Enter a unique, descriptive test
dataset name.
Once the setup is complete, the load will be applied at a rate of 0.003 inch per inch of the
specimen length per minute. The specimen will be loaded until the proportional limit is passed.
This may occur around 20 kip, depending on the sample species. Photograph the failed specimen.
Accentuate the rupture plane by using a pen or pencil to trace the failure surface to make it easily
seen in the photograph.
Report Requirements
The following information must be included in the report:
1. Brief description of the lab (memo);
2. Summary of results, including specimen dimension (inch), maximum load (kip),
maximum compressive stress (ksi), strain at maximum load, E (ksi);
3. All measured data;
4. All calculated data;
5. Load-Deflection curve plot;
6. A sketch of the rupture pattern in the wood sample tested to failure.
Sample Calculations
Note: Erroneous data may be thrown out of the calculations as long as there is sufficient correct
data to support your work.
6” Specimen, 1.5 inch x 1.5 inch cross-section  2.25 inch2
Load is applied parallel to the grain
Deflection = Δ = strain (as a decimal number) * 4 inch (gage length) = 0.02 * 4 inch = 0.08 inch
Stress = P/A = 0.73 kip/2.25 inch2 = 0.324 kip/inch2 (ksi)
E = Stress/Strain (slope of linear graph) = (0.622-1.96)/(0.03-0.08) = 26.76 ksi
Department of Civil Engineering, Southern Illinois University Edwardsville 2/5/2010
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