The Effect of Truss Type on Mass Supported Before Failure

Researched by Camdon A.
2003-04

PURPOSE
 

The purpose of this experiment was to determine the effect of wooden truss type on the mass supported before failure.

I became interested in this idea because I have three older brothers who are or interact with contractors and carpentry and deal with this every day.

The information gained from this experiment could be helpful to home buyers, home owners, carpenters, contractors, architects, and any one else involved in the buying, designing and building of houses and buildings.  

HYPOTHESIS
 

My hypothesis was that the more web members in the truss the more mass the truss would support.

I based my hypothesis on a science project done in the year 2000 by Aaron John. The conclusion to the experiment was the king post with struts (web members) held more weight than the queen post and the king post without struts.

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EXPERIMENT DESIGN

The constants in this study were: 
* Length of truss
* Span of truss
* Type of wood
* Dimensions of wood
* Type of glue
* Building procedures 
* Testing procedures
* Scale used to determined mass 
* Type of load used to test the truss

The manipulated variable was the type of truss.  

The responding variable was amount of mass held by the truss before failure.  

To measure the responding variable I used a bathroom scale that measured in kilograms.

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MATERIALS

QUANTITY ITEM DESCRIPTION
1 Bottle of glue
1 Bathroom scale
1 100 lb. of sand
2 9 pieces of 1/16x 1/4 balsa wood
1 Tape measure
1 Pulley 
2 Saw horses
1 18x 10 inch piece of 3/4 inch particle board
1 Five inch piece of 2x2
1 Five-foot piece of 1/8 inch string
1 Five gallon Rubbermaid tub

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PROCEDURES

1. Make truss holder to fit a 6/12
a. Cut a piece of 1x4 that is 1 1/2 square inches 
b. Cut two pieces of the balsa wood to have a 45* angle on one end and be 1 1/4 inches long
c. Glue the two pieces of balsa together at the 45*angles to make a 90* angle 
d. Glue both pieces of 1x4 to the balsa to were the peak of the balsa, in the middle, is pointed to the top of the 1x4 pieces 
e. Once dry cut 1/4 inch groove down middle of the top and bottom
2. Next step make the truss span
a. Cut four pieces of 2 1/2x 1 inch oak two to be 3 inches long, and two to be 2 1/2 inches long 
b. Screw the 3 inch long ones down to the piece of particle board (screwed to two saw horses), three and a half inches apart, with a 1 1/4 inch screw
c. Screw the 2 1/2 inch long ones down on top the three inch one, one inch in from the side and one inch from the top with a 1 1/4 inch screw
d. Cut the piece of 2x2 in half and screw it on a 45* angle 4 3/4 inches in from the side, and 2 inches from the bottom
e. Screw pulley in 8 1/2 inches in from the side of the particle board and 1/2 inches in from the bottom of the particle board
3. Cut wood to appropriate size and angle for the main body for all trusses (upper and lower cords) 
a. For the top cord cut 18 pieces of the balsa to be 5 1/4 inches long with a 45* angle on both ends
b. Cut another piece of balsa into 9 pieces that are 8 inches long also with two 45* angles on each end 
4. Cut the web members for the King trusses
a. Cut 3 pieces of balsa to be 4 3/8 inches long with two 45* angles on one end to make a 90* point, and a 90* angle on the other end 
5. Cut web members for a Queen truss
a. Cut 3 pieces of balsa to be 4 3/8 inches long with two 45* angles on one end to make a 90* point, and a 90* angle on the other end 
b. Cut 6 more pieces of balsa to be 4 1/4 inches long with a 45* angle on one end and a 90* on the other end
6. Cut web members for a Howe truss
 a. Cut 3 pieces of balsa to be 4 3/8 inches long with two 45* angles on one 
  end to make a 90* point, and a 90* angle on the other end 
b. Cut 6 more pieces of balsa to be 4 1/4 inches long with a 45* angle on one end and a 90* angle on the other end
c. Cut 6 pieces of balsa to be 2 1/2 inches long with a 45* angle on one end and a 90* on the other end
7. Glue king truss together
a.   Take two of the top cord pieces, that are 5 1/4 inches long, and glue them 
  together at the 45* angle forming a 90* angle
b.   Take one of the bottom cords and glue it to the two top cords forming a smooth slop down the side of the triangle
c.   Glue the web member in so the 90* point sits in the inside peak of the truss and the other end sits flat on the lower cord
8. Glue Queen truss together
a.   Take two of the top cord pieces, that are 5 1/4 inches long, and glue them 
  together at the 45* angle forming a 90* angle
b.   Take one of the bottom cords and glue it to the two top cords forming a smooth slop down the side of the triangle
c. Glue the web member in so the 90* point sits in the inside peak of the truss and the other end sits flat on the lower cord
d. Out from the first web member glue on two of the 4 1/4 one on each side, making a total of four triangles inside the truss
9. Glue Howe truss together
a.   Take two of the top cord pieces, that are 5 1/4 inches long, and glue them 
  together at the 45* angle forming a 90* angle
b. Take one of the bottom cords and glue it to the two top cords forming a smooth slop down the side of the triangle
c. Glue the web member in so the 90* point sits in the inside peak of the truss and the other end sits flat on the lower cord
d. Out from the first web member glue on two of the 4 1/4 one on each side, making a total of four triangles inside the truss
e. Off of the second web member glue on a two of the 2 1/2 so the 45* angle leans on the second web member and the 90* angle is on the lower cord
  10. Start tests for King truss
a. Put one King truss in the truss span
b. Put string connected to five gallon tub, and threw the pulley, in groove on the truss holder
c. Put truss holder on one of the three King trusses
d. Poor sand into five gallon tub until truss breaks
e. Weigh tub, sand, truss holder, string and then record 
f. Do procedures 10a-10e for all other King trusses
  11. Start tests for Queen truss
a. Put one Queen truss in the truss span
b. Put string connected to five gallon tub, and threw the pulley, in groove on the truss holder
c. Put truss holder on one of the three Queen trusses
d. Poor sand into five-gallon tub until truss breaks
e. Weigh tub, sand, truss holder, string and then record 
f. Do procedures 11a- 11e for all other Queen trusses
  12. Do tests for Howe truss
a. Put one Howe truss in truss span
b. Put string connected to five gallon tub, and threw the pulley, in groove on the truss holder
c. Put truss holder on one of the three Queen trusses
d. Poor sand into five gallon tub until truss breaks
e. Weigh tub, sand, truss holder, string, and then record 
f. Do procedures 12a- 12e for all other Howe trusses

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RESULTS

The original purpose of this experiment was to determine the effect of truss type on the mass supported before failure.

The results of the experiment were, the average weight held by the King truss was 2. 5 kg, the average held by the Queen truss was 3. 8 kg, and the average held by the Howe truss was 6. 5 kg.

See my table and graph below.

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CONCLUSION

My hypothesis was that the more web members in the truss the more mass the truss would support.

The results of this experiment indicate my hypothesis should be accepted because of the average of the King truss being 2. 5, the average for Queen truss being 3. 8, and the average for the Howe truss beings 6. 5. This means the more web members the more weight the truss held.

Because of the results of this experiment, I wonder if the type of testing would affect the mass held. I also wonder if the type of wood would affect the strength 

If I were to conduct this project again I would think out the experiment more thoroughly and think of a different way to support the truss while it is being tested so the truss would not twist and break before the total amount of mass is put on it correctly.

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RESEARCH REPORT
 

Introduction

A truss is a structural design used in a house or building roof or a bridge to support mass that is put on it. A truss is made mainly by configuring triangles, which have the principal of “a triangle is a rigid configuration that cannot collapse, or change its shape. ” Aaron John 1999-2000 science project
 

Trusses

The types of trusses I tested by mass were King-post, Queen-post, and Howe. They all had one common design beam. They all had a middle web member that supported the peak of the truss. The King-post design only has the middle web member supporting the peak. The other trusses (Queen-post and Howe) both have horizontal web members, going out from the bottom of the middle web member, to support the upper cords. The only thing different between the Queen-post and the Howe are from the horizontal web members, coming from the middle web member, is another web member going down to the bottom cord to divide the mass on the upper cord, evenly between the bottom cord.
 

Structure of Buildings

Buildings have two parts. One is the superstructure (the part of the building above ground level). The superstructure is most commonly referred to as the framing. The substructure has the basement walls or the foundation. Both the substructure and the superstructure help to support the weight of the building or the “dead load”. The dead load is the total weight of all its parts like the roof, and any pressure. Wind pressure is part of the dead load and is called the “wind load”. There are many other kinds of loads like, snow load, or earthquake shock. These kinds of loads are important for a building to stand up to because they can be very common.
 

Shelter for Us

Trusses are one of the most important parts of a shelter (house). If on a house there was no truss many harmful things could happen. Rain, snow, wind, heat, cold and any other natural disaster could come in. With a truss people can heat and cool there houses easily and shed rain, snow, wind letting them live safer and more comfortable.  
 

History

“In the 18th Century mathematics learned how to apply their science to the behavior of structure and making it possible to determine the amounts of the stresses in deferent places in buildings. This info led to the development of space frames, which are trusses, or other parts arranged three-dimensionally.  

The Romans were on of the first to come up with building trusses.   They made them to span large open spaces in buildings that use post and lintel construction. Also in Rome truss descriptions were made by roman Architect, Vitrivius De Architura.  

During the 19th Century cast iron, wrought iron, and also steel became the preferred truss material, because of how strong and supporting steel, and other metals are. ” Aaron John 1999-2000 science project
 

Summary

Trusses are used to support building roofs. They are triangle shaped and have posts that are in the triangular shape that supports the truss from the sides. Some of the types of trusses are the King-post, Queen-post, and Howe.  

There are two parts to a building, the superstructure and the substructure.   The superstructure is the part of foundation above ground level. The substructure is the foundation below ground level. Basements are considered part of the substructure.  

Trusses are one of the most important parts of a house. If a house had no trusses many harmful things would happen.

In the 18th Century mathematics learned how to apply their science to the behavior of structure and making it possible to determine the amounts of the stresses in buildings.

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BIBLIOGRAPHY
 

Beer, Ferdinand P. , and Johnston, E. Russell Jr. Vector Mechanics for Engineers. New York: McGraw-Hill Inc. p. 223- 27.

Cunningham, David. “Types Of Wood,” World Book Encyclopedia, 2001.

Dettman, Mathew A. “Concrete,” ENCARTA Encyclopedia Deluxe, 2001.

“Maple Valley Truss. com,” Truss Types November 05, 2003. http://www. maplevalleytruss. com/config.html 

“Parts Of Trusses. com,” Parts Of Trusses November 05, 2003. http://www. jessmine. k12. ky. us/ejms/teched/bridge/truss2.html 

“Roofing- Trusses” Trusses October 24, 2003. http://doityourself. com/roofing/rftrusses.htm 

 Temasetti, Richard L. “Building Construction,”  ENCARTA Encyclopedia Deluxe, 2001.

“Truss Plate Institute, Inc” History November 12. 2003. http://www. tpinst. org/my_foundation.html 

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ACKNOWLEDGEMENTS

I would like to thank the following people for helping make my project possible:

* My mom for helping me get all the materials needed for this project
* My dad for helping conduct and come up with new testing ways
* Heidi Herzog for letting me barrow “Vector Mechanics for Engineers”.
* My science teacher for keeping me on track and in the right direction 
 
 

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