PURPOSE
The purpose of this experiment was to determine which of three truss designs would hold the most mass.
I became interested in this idea when I found out that roofs of buildings had trusses. I wondered how much weight trusses could hold before collapsing.
The information gained from this experiment could help engineers better understand which of the three designs of trusses could hold the most load. Also people who live in areas with lots of snowfall or high wind need strong roofs built with well-designed trusses.
HYPOTHESIS
My hypothesis was that the King-post truss would hold the most mass.
I based my hypothesis on a previous study done in 2000 by 6th grader Aaron John, “Mass supported by King-post and Queen-post Truss Designs.” He concluded” that the King-post design was the most successful by standing the most weight.”
The constants in this study
were:
• Method force was applied to each truss.
• Type of wood used to make each truss.
• Vernier force probe used to measure the force on the truss before collapsing.
• The size of each truss.
• Laptop to record the data.
• Glue used to build the trusses.
The manipulated variable was the truss design.
The responding variable was the amount of force each truss could withstand before failure.
To measure the responding variable, I used a Vernier force plate attached to a laptop running Logger Pro 3.1 software.
MATERIALS
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QUANTITY
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ITEM DESCRIPTION
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3
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Thin balsa wood sticks
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|
1
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Vernier force plate
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1
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Notched wooden block
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|
1
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Laptop
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1
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Hot glue gun
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1
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Glue
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PROCEDURES
1. Building the trusses.
a) Buy
several pieces of thin balsa wood.
b) Hot glue three wood pieces in the shape of a triangle, 15 cm long on each side
c) Hold the part of the truss you are gluing for 60 seconds so it will set.
d) Make sure each truss is the same size.
e) Repeat steps b-d eight times so you have a total of nine trusses.
f) Start building the main vertical struts that are going to be inside in every truss design.
g) To make it easier, angle the cuts on the struts so they into place better.
h) Hot glue the struts inside the trusses from apex down to center of the bottom member.
i) Build all nine trusses to have this center post.
j) Set three of these trusses aside and label “King-post”
k) Take three of the basic trusses and add additional struts to make Queen-post trusses. They need mini-struts hot glued going from the bottom of the center post out to the center point of the side members. Set aside and label as “Queen-post”.
l) Take three of the basic trusses and add additional struts to make Graf-post trusses. They need mini-struts hot glued going from the bottom corners of the truss to the center point of the center post. Set aside and label as “Graf-post”.
m) Create a notched wooden block for applying force to the apex of the truss. The notch in the wood exactly the angle of the apex on the truss.
2. Setting up force
system.
a) You
should have a Vernier force plate and a computer to do this experiment.
b) Set up
the computer so it can read the force recorded from the force plate using
Logger Pro interface box.
c) The computer has to have a Logger Pro 3.1 software, so it
can read the force recorded from the force plate.
d) Make sure the force plate is connected during the
experiment when measuring the force of each truss design before failure.
e) Calibrate the force plate to read zero when no force is
applied.
3. Testing truss 1
a)
Apply force straight down on the truss so the force plate can read the
force and send the information to the computer.
b) Apply force by using the notched wooden block.
c) Put the bottom of the truss on the force plate and put the notch on the top angle of the truss.
d) Start the data collection of the computer.
e) Start applying steady force with your hand.
f)
You need to keep adding more and more force until the truss finally
breaks.
g)
Once the truss actually breaks, then go over to the computer and record
the highest force just before failure.
h) Do the same thing for trial 2 and 3 by repeating steps 3a-3f.
4. Testing truss 2
a) To
test truss type 2 repeat steps 2-3.
b) Be sure to conduct 3 trials
5. Testing
truss 3
a) To
test truss 3, repeat steps 2-3.
b) Do the same thing for all three trials.
c) For each truss find the average of force from the three trials.
d) Use the average results to compare the truss designs.
6. Compare
The original purpose of this experiment was to determine which of three truss designs would hold the most mass.
The results of the experiment were that the Graf-post held 214 newtons, the Queen-post held 175 newtons, and the King-post held 129 newtons.
CONCLUSION
My original hypothesis was that the King-post truss would hold the most mass.
The results indicate that this hypothesis should be rejected, because the Graf- Post truss held more force before failure than the King-Post.
After thinking about the results of this experiment, I wonder if the type of wood would make a difference in the outcome of the results. Then I also wondered if the type of glue would make a difference.
If I were to conduct this project again I would build and test many more models of each type, probably 10. I would be more exact when cutting and fitting the struts. Then I would test a couple more types of typical truss designs. I would also build my trusses so the bottom member was stronger than the sides.
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