Does the Peak Angle of a Truss Affect its Strength?
Researched by Logan D. 2001-02	PURPOSE  HYPOTHESIS  EXPERIMENT DESIGN  MATERIALS  PROCEDURES  RESULTS  CONCLUSION  RESEARCH REPORT  BIBLIOGRAPHY  ACKNOWLEDGEMENTS  ABOUT THE AUTHOR

The purpose of this experiment was to determine how the peak angle of a truss affects the mass it will support before failure.

I became interested in this idea when a homebuilder was telling me about different roof designs.

The information gained from this experiment may help architects to decide at what angle to build trusses to maximize strength. 

My hypothesis was the truss with the largest exterior peak angle would support the most mass.

I base my hypothesis on Max Dodd, a homebuilder who stated that a truss with a steeper peak would support more weight. 

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The constants in this study were:

* The span of the truss
* The amount of glue used 
* The length of the truss
* The material the truss was made of (balsa wood)
* The cross sectional size of the wood used to build the truss
* The support system
* The design of the truss
* The testing procedure 

The manipulated variable was the peak angle of the truss.

The responding variable was the amount of mass supported before failure.

To measure the responding variable I continued to load the truss with weights until it failed. Then I weighed the load using a triple beam balance.

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1. Gather materials.
2. Build the chords (outer part) of truss.
3. Cut 45-angle slant in each end of the wood pieces making sure they are slanted in the same direction.
4. Pin wood together in a triangle form to make sure they fit (some of the side chords will go of the side).
5. Put one drop of glue on each end and repin until dry.
6. Mark with the pencil 6in. on each piece except on the bottom chord mark the 12 in line also. 
7. Build the web (inner part) of the truss.
8. Cut 45-degree slants in each piece of wood making sure that the slants are in the same direction.
9. Pin together in W form so they line up with the marks made during step 6 to make sure they fit.
10. Add glue. 
11. Repeat steps 2-15 except make cuts at 40 degrees.
12. Repeat steps 2-15 except make cuts at 35 degrees.
13. Slide into place; hold until dry.
14. Fill in weak spots with glue-covered toothpicks. 
15. Put truss on scale and record weight.
16. Build support/testing system
17. Put the two large pieces side by side and put the small pieces on top at the ends.
18. Glue in place wait until dry then turn over.
19. Drill four holes in wood on the topside, but not all the way through.
20. Glue poles in holes.
21. Drill four holes in block of wood to match poles.
22. Place truss in the gap in the middle.
23. Slide block on truss through the poles lubricate with soap if needed.
24. Place bucket on top of block.
25. Load sand in the bucket until failure.
26. Weigh amount of sand and record data.
27. Repeat steps 16-24 for second truss.
28. Repeat steps 16-24 for third truss. 
29. Repeat steps 1-28 for trial #2.
30. Repeat steps 1-28 for trial #3.
31. Compare data. 

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The original purpose of this experiment was to determine how the peak angle of a truss affected its strength.

The results of the experiment were that the 4-12 held the most weight with an average of 4315 grams supported. The 6-12 truss held the second most with an average of 3233 grams supported. The 8-12 truss held the least with an average of 2953 grams supported.

See data and graphs.

My hypothesis was that truss with the largest exterior peak angle will support the most mass.

The results indicate that this hypothesis should be rejected. 

Because of the results of this experiment, I wonder if building material, especially type of glue would affect its strength.

If I were to conduct this project, again I would buy balsa wood in strips instead of cutting my own so they would be more similar in width. I would also conduct more trials using more truss types, such as 3-12, 5-12, 7-12, and 9-12.
 

Research Report   "Truss: an assemblage of members (as beams) forming a rigid frame work" Merriam-Webster Dictionary Introduction      In architecture and engineering a truss is a structural support used like a beam. A truss requires fewer materials than a solid beam in roof and bridge design. It is based on the principle that a triangle cannot change its shape and is very rigid.      A basic truss is a braced triangle frame used to hold up a roof. A more complex truss is made up of several triangles that make a unit capable of holding large amounts of weight over a long span. The connecting top and bottom pieces are called chords. The pieces inside the chords are called the web. History        Greek builders invented the truss in 300 B.C. The earliest truss descriptions are from the Roman architect Vitruvius in his "De Architectura", on which the architectural pattern for the Renaissance was based. In the 18th and 19th centuries cast and wrought iron were brought into use, but in the 20th century they became obsolete and steel was used. Truss bridges      Truss bridges are built over canyons, rivers, and other areas. A truss bridge can have a main span of over 1000 ft (300 meters). Each truss is made up of steel or wood parts that are connected into 1 or more triangles. Most truss bridges have a set of trusses with the road on top. These are called deck truss bridges. Bridges where the road runs through the trusses are called through truss bridges. In basic span truss bridges each truss extends between two abutments or piers. In a continuous truss bridge each truss has 3 or more of these supports.       In some places the area is appropriate for either a truss or a girder bridge. In these cases engineers often chose a truss bridge because it requires less material than a girder. Sometimes engineers chose to use a girder because they are more attractive and easier to take care of.  Kinds of Trusses      There are two main kinds of trusses: flat and peak, with many kinds branching off those. Kinds of peak trusses include Simple, Kingpost, Queenpost, Pratt, Warren and many others. The chords of all trusses are the same in a simple triangle shape except flat trusses which are the shape of a rectangle. The web is the only thing that varies. A Simple truss’s web is in the shape of W. A Kingspost’s web is very basic with just a pole in the middle. Flat trusses’ webs are just X’s.      Trusses are used in houses, skyscrapers, aircraft fuselages, car frames and many other things.  Trusses are measured with two numbers. The second is always 12 and the first varies. For every 12in. in length it goes up in the center whatever the first number is. For example an 8-12 truss that is a foot long is 8 inches tall.  Foundation of Trusses       Buildings are made up of two parts; the substructure and the superstructure.  The substructure is the part of the building underground and the superstructure is the part of the building above. The substructure is usually considered the foundation which includes the basement walls. Girders, beams, columns, and trusses make up the superstructure and support the weight of the building and the dead weight. The dead weight is wind, snow, furniture, people, and other pressure.  Summary        Trusses provide safe shelter for people. They provide them with transportation in cars, and airplanes and ways to cross-large areas through bridges. Top of page

BIBLIOGRAPHY Paulson Jr. Boyd C. "Building Construction." The World Book Encyclopedia. 1999. Max Dodd, Personal interview, December 15,2001  "Truss." Academic American Encyclopedia. 1990. "Truss." American Encyclopedia. 1999. "Truss." Merriam-Webster Dictionary. 2001. Videon, Fred F. "Bridge." The World Book Encyclopedia. 1999.

ACKNOWLEDGEMENTS
I would like to thank the following people. Without their help my project would not of been possible.
* My mom for transporting me to and from SOAR.
* My dad for helping me build my support/testing system.
* Mrs. Helms for helping me with my project.
* My friends Sean and Kyle for listening to my presentation.
* Mr. Newkirk for helping me with my project and journal.

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