Which Bridge Type Would Support the Most Mass?
Researched by Sean K. 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 which type of bridge could support the most mass.

I became interested in this idea when I built a toy bridge in 4th grade and wondered if it would be stronger or weaker if I built it in a different way.

The information gained from this experiment could help civil engineers decide which type of bridge would be most suitable for a particular location based on the amount of weight the bridge could sustain.

My hypothesis was that a cable?stayed bridge would support the most weight before it failed.

I based my hypothesis on the research previously done by Tim Smith when he was a 6th grade student. As shown on http://www.selah.K12. wa.us /soar/Science Project 2001/TimS.html#Results which states, "…The cable-stayed bridge held the most weight…"

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The constants in this study were:

• The lengths of the bridges
• The widths of the bridges
• The materials used to make the bridges
• The methods used to make the bridges 
• The spans of the bridges
• The methods of testing
• The types of weight used (sand)

The responding variable was the weight supported by the bridge before it failed.

To measure the responding variable, I used a balance scale to determine the weight of the load in grams.

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A. Build the Arch Bridges:
1. Gather all of your materials.
2. Begin to make an Arch Bridge by selecting two 10cm x 5cm x 5cm blocks of balsa wood for the bridge piers.
3. Cut a piece from each block 7cm tall x 5cm wide x 1cm deep, so that the pier blocks look somewhat like "L"s from the side when you are finished.
4. Stand up the pier blocks 54cm from one another with the base of the "L"s facing each other.
5. Select three 58cm x 5cm x 2mm pieces of balsa wood.
6. Laminate the three pieces together with the wood glue.
7. Before the glue dries, bend the three laminated pieces of balsa wood into an arch that spans 54cm.  Use a large furniture clamp to hold the arch at 54cm and spread out three small clamps to clamp the glued pieces of balsa wood to one another.
8. Once the arch has dried, glue the ends into the notches of the shaped piers
9. Select a 90cm x 5cm x 2mm piece of balsa wood to use as a roadway.
10. Center the roadway across the piers and glue it to the top of the "L"-shaped piers and the top center of the arch.
11. Select a 5cm x 1.5cm x 6mm piece of balsa wood. Position the piece of balsa wood with the 1.5cm dimension vertical, and slide it between the arch and the roadway toward the middle of the bridge until it is snug between the top of the arch and the underside of the roadway. Then glue it in place.
12. Repeat step 11 for the other side of the arch. 
13. Select a 5cm x 3cm x 6mm piece of balsa wood and glue it in place with the 3cm dimension vertical in the same manner as step 11.
14. Repeat step 13 for the other side of the arch.
15. Select a 5cm x 4.5cm x 6mm piece of balsa wood, and position it with the 4.5cm dimension vertical, then glue it in the same manner as step 11.
16. Repeat step 15 for the other side of the arch.
17. Select a piece of lumber that is 8.9cm x 3.8cm x 91.4cm to use as a base for the bridge. Mount the bridge to the pieces of wood by centering the bridge on the piece of lumber and gluing the bottoms of the bridge piers to the lumber base. Then carefully turn the bridge and base upside down and drive one 7.6cm screw through the lumber base and into each pier
18. Repeat steps 2-17 three more times (to produce three bridges for testing and one for display).
19. Set these Arch bridges aside for now. 

B. Build the Suspension Bridges:
20. Begin a Suspension bridge by selecting two 10cm x 5cm x 5cm blocks of balsa wood for the bridge piers.
21. Stand the two piers 54cm apart with the 10cm dimension vertical.
22. Select a 90cm x 5cm x 6mm piece of balsa wood for the roadway, and center the roadway across the two piers, then glue the roadway to the top of the piers.
23. Select two 20cm x 5cm x 5cm pieces of balsa wood for the bridge towers. Drill two holes at one end of each of the towers. Position the holes 1cm from the end and 0.5cm from the edges. 
24. Stand the towers with the 20cm dimension vertical and glue the towers to the top of the roadway 54cm apart, directly above the piers, making sure that the holes are at the top of the towers and that the holes face the ends and the center of the bridge.
25. Repeat step 17 for this bridge.
26. Drill two 1/8 in. holes near each end of the roadway positioning each hole 3.8 cm from the end of the roadway and 1/2cm from the edges of the roadway.
27. Select four 3.8cm screws to use as cable anchors. Screw two screws into each end of the lumber base, positioning each one so it is in line with the holes drilled at the ends of the roadway
28. Cut eight pieces of string 250cm long. Twist the four strings together to form one of the top, main cables for the bridge. Twist the other four strings together to form the other top main cable. 
29. Tie one end of a main cable to an anchor screw at the end of the lumber. Then, using a large needle, thread the cable up through the nearest roadway hole above the screw anchor and then through the top of the nearest tower. Next, thread  through the hole at the same position in the second tower, then down through the corresponding hole at the other end of the bridge. Pull the cable tight enough to leave about 3cm sag at the end of the middle between the towers. Tie the end of the cable to the corresponding screw anchor. Cut off excess cable.
30. Repeat step 29 for the other side or the bridge.
31. Drill 1/16in. holes at 3cm intervals along each side of the bridge. The holes should be located 0.5cm from the outside edges of the roadway.
32. Tie single pieces of string at 3cm intervals above each of the holes to one main cable. Thread each string down through the hole below and then across the underside of the bridge, and then up through the hole that is directly across. Tie each string to the other main cable directly above each hole making sure the strings are quite taut. 
33. Repeat steps  20-32 three times to produce three more bridges, one for display and         three for testing.
34. Set the completed Suspension bridges aside for now.

C. Build the Cable-stayed Bridges:
35. Begin a Cable-stayed bridge by selecting two 10cm x 5cm x 5cm pieces of balsa wood to use as piers. Stand the piers on end with the 10cm dimension vertical, and position the piers 54cm apart.
36. Select a 90cm x 5cm x 6mm piece of balsa for a roadway. Center the roadway on the piers and glue it to the tops of the piers.
37. Select two 20cm x 5cm x 5cm pieces of balsa wood to use as bridge towers. With a saw, taper the towers’ lengthwise so that the base remains 5cm wide and 5cm deep but the top is reduced to 1cm wide (but remains 5cm deep).
38. Drill a hole near the top of each of the towers using a 3/16-drill bit. Position the holes 1cm below the top of each tower, centering the holes on the 1cm side of the towers.
39. Position the towers directly above each of the piers and glue the towers to the roadway surface, being sure to position the towers so that their "A" shapes face the center and ends of the bridge.
40. Drill a row of 1/8-inch holes along one side of the roadway. The holes should be placed 1/2cm from each side of the bridge. Starting at one end of the bridge, begin with a hole placed 1/4cm from the end (and 1/2cm from the edge of the bridge) and space the next four holes at 3cm intervals.
41. Repeat step 40 with a corresponding set of holes at the opposite end of the bridge.
42. Drill a row of nine holes between the towers, placing them in line with the holes already drilled at each end of the bridge. The first of these holes will be placed 3cm from one of the towers along the roadway between the two towers. The next eight holes need to be drilled at 6cm intervals in line from the first hole. 
43. Repeat steps 40-42 for the opposite side of the bridge.
44. Repeat  step 17 for this bridge.
45. Select two cup hooks. Screw one cup hook into the top of the lumber base at a location centered 3 inches from the end of the lumber base. Repeat with the second cup hook at the other end of the base.
46. Using approximately 2 meters of string for the bridge cables, thread the string on a needle. Leaving the string doubled, tie the loose end onto one cup hook, and then thread the doubled string up through one of the holes that is closest to the tower. Then, thread the string through the hole in the top of the tower and then down through one of the holes that are at each side of the center of the bridge. Next, pass the string to the underside of the bridge and up through the hole that is on the opposite side of the bridge. Thread the string back through the same tower and then down through the other hole that is nearest the outside of the tower and which is opposite the hole, which you started with. Then, pull the string tight and tie it off at the cup hook with a large knot. Cut off any excess string.
47. Repeat step 46 over and over again, threading the successive holes in order, until all of the holes on that end of the bridge have been filled.
48. Repeat steps 46-47 for the other end of the bridge.
49. Repeat steps 35-48 three more times to produce a total of four cable-stayed bridges, three for testing and one for display. 

D. Set up Experiment Area.
50. Get two saw horses and set them about 45cm apart

E. Conducting the Experiment/Testing:
51. Select a 1.9cm x 1.9cm x 30.5cm piece of wood and place it in the center of one of the  arch bridges so that it doesn’t stick out on the edges. 
52. Then select a 3.2cm x 1.9cm x 15.24 piece of wood and place it on top of the 1.9 x 1.9 x 30.5cm wood so that the edges stick out. 
53. Secure a heavy wire loop around each end of the 3.2 x 1.9 x 15.24 then tie it to the bucket  Next, slowly add sand to the bucket until the bridge fails. Once the bridge has failed, weigh the quantity of  sand in the bucket.
54. Repeat steps 51-53  with two more of the arch bridges. until you have completed two more trials.
55. Repeat steps 51-53 for three of the suspension bridges.
56. Repeat steps 51-53 for three of the cable-stayed bridges.
57. Finally, record the data.

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The original purpose of this experiment was to determine which type of bridge could support the most mass.

The results of the experiment were that the cable-stayed bridge held the most mass for all three trials, with an average weight of 21.6 kilograms. The suspension bridges held the least amount of mass on the average, with the average weight of 12.2 kilograms.

See data and graphs

My hypothesis was that a cable?stayed bridge would support the most weight before failing.

The results indicate that this hypothesis should be accepted because the cable-stayed bridge held the most mass.

Because of the results of this experiment, I wonder if I had used a different type of material to build my bridges or varied the  method of building my bridges, if the results be similar.

If I were to conduct this project again,  I would conduct several more trials, I would also measure the weight of the mass with a more specific scale.  I would also make the suspender cables on the suspension bridges twice as strong because it might have been a fairer test. 

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RESEARCH REPORT Introduction Bridges are very important to human transportation, especially since cars were invented and more bridges and highways were needed. Bridges are useful to humans because they can cross obstacles like canyons, rivers, and bodies of water instead of going around the long way. History  Bridges have been in use for several thousand years and still prove to be of great use. Probably the first bridges were logs thrown over a river.  Some historians believe that the first arch bridges were built in Babylon, China, Egypt, Greek, and Rome.  The first movable bridges were called drawbridges and were built in the Middle Ages.  These bridges were built to protect the kingdom in a castle and could move up and down and were placed over moats. Many early bridges were made out of stone and wood until cast iron came into wide use. Truss bridges were developed in the 1500’s. The first suspension bridges were built in the 1800’s. The roadways were hung from wrought iron chains. The first girder bridge was finished in 1847. The modern cantilever bridge was first built in 1870. Steel became the main bridge building material in the late 1800’s. The first concrete bridge was built in 1869. Reinforced concrete was introduced to bridge building immediately after 1869. During the 1930’s prestressed concrete became an important bridge building substance. The first modern cable stayed bridge was introduced in 1955.    Types of Bridges     Suspension  Suspension bridges have very long spans and are mainly used over steep canyons or deep water. Most people think of suspension bridges as awe-inspiring or very beautiful. All suspension bridges have roadways that hang from very strong steel cables. Two very tall towers support these massive bridges. This type of bridge is used for great distances and some have main spans as long as 4000 ft. Suspension bridges use only two piers, which support the whole bridge. The side spans of the bridges stretch from the tower to the anchorage. The top main cables stretch from one side of the bridge to the other. Most anchorages are huge blocks of concrete that are placed at each end of the bridge. The top main cables are attached to the top of the suspender cables. The bottom of the suspender cables is attached to the roadway. These bridges sway in very hard wind. The Tacoma Narrows Bridge was given a nickname of "Galloping Girdy," and eventually the bridge collapsed.  Arch The span of the arch bridge forms the arch and is the main strength of that type of bridge. Arch bridges’ main span can be as long as 1700 ft. This type of bridge is on of the oldest designs. Some older arch bridges were made of stone blocks that were wedged together to make an arch. Many arch bridges have short spans that are made of concrete and steel. While long spanning arch bridges are made of concrete or steel. When the arch is below the roadway, there are supports between the roadway and arch called spandrel columns. These    supports transfer the weight of the roadway and all the objects on it to the arch. When the arch is on the bridge, there are girders coming out of the bridge and supports the roadway and the arch also supports it.  Cable Stayed  The cable-stayed bridge is a variation of the suspension bridge. This type of bridge has tall towers like a suspension bridge. The cables are directly attached to the roadway by a series of diagonal cables. These bridges are built like a suspension bridge but this type of bridge has no top main cables. Cable stayed bridges are used for intermediate size spans. Cable stayed bridges can have either two towers or one. These bridges are most effective when over 700 feet long. The towers on the cable-stayed bridge were some times called pylons. Each deck section of a cable-stayed bridge pulls down on a cable. This effect makes the cables pull on the towers, which transfer the weight to the ground. Building Bridges  Suspension Bridge  When building a suspension bridge you should place the piers first, then you place the towers on top of them. Once this is done, build the anchorages at each end of the bridge. After that you must make the top main cables and place them in the anchorage through the tower and place the cable in the anchorage. Do the same with the other side of the bridge. Then place part of the roadway and two suspender cables where they would hook on the roadway. Do this for the rest of the bridge. You should start from the tower and keep going toward the center and out to the anchorages.  Arch Bridge  Place the two piers in their selected spots. Then place the arch between the two piers very firmly. Then put the spandrel columns between the arches. Once that is finished, now place the roadway on top of the arch and spandrel columns.  Cable Stayed Bridge   The only difference between building the suspension bridges and the cable-stayed bridge is the stringing. Place the roadway. Then you must place one cable firmly into the roadway. String the cable through the tower and back onto the other side of the roadway. Then continue this pattern for the rest of the bridge. Make sure that you leave at least 20 feet between each cable. Summary Bridges are very use full to the human s transpiration because they can help them cross obstacles such as canyons, and bodies of water. Bridges also need to be safe because people use bridges so much. Top of page

BIBLIOGRAPHY Chris Oxlade Superstructures Bridges Austin, TX Raintreesteck Vaughn Publishers 1997 4, 16-24 Keith Willard Bridges Mankato, Minnesota Creative Education 2000 16-20 MacGregor Scott and Anne Bridges a Project Book New York Lothrop, Lee and Shepard Books 1980  Paulson, C. Boyd "Pontoon Bridge" The World Book Encyclopedia  Schultz, B. Cameron and Graves A. Dimitri "Bridge" Encarta 2001 Videon, F. Fred "Bridges" The World Book Encyclopedia 1999

ACKNOWLEDGEMENTS

I would like to thank the following people. Without their help my project would have not been possible.

* My mom for taking me to SOAR  and after school SOAR
* My dad for helping me build my bridges and taking me to buy balsa wood
* My friends Kyle and Logan for listening to my presentation 
* Mrs. Helms for helping me with my display
* Mr. Newkirk for helping with my project and journal 
 
 
 

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