Bridge of Arc’s Design Brief

Introduction:Statement of Inquiry: How do design limitations encourage creativity in technology?Key Concepts: DevelopmentRelated Concepts: ResourcesDesign Specification: In groups of two students will design and create popsicle bridge based on the student’s investigation. Students will then test their design and refine their product after testing. The bridge that holds the most weight will be declared the class winner.Materials: • 75 popsicle sticks• 3 glue gun sticks• Drafting and sketching paperRules: Only the given materials must be used nothing more Maximum Hight of Substructure and Super Structure is 20cm Minimum Length must be 30cm Minimum Width should be 10cm

Investigation

To design a well functioning bridge, research about the science and physics behind bridges was required.

Forces and terms needed to understand : Compression, Tension, Shear, Torsion, Bending, Deflection, Load (live and dead), Racking. These terms should be known for communication purposes. Designs should also be made with these forces as factors in them.

Types of bridges, their strengths and weaknesses also needed to be known. The knowledge of the bridges would help to inspire us in the planning for our design.

"A." Glossary of Bridge Terminology--. Lichtenberger Engineering Library. Web. 17 Dec. 2014. <http://sdrc.lib.uiowa.edu/eng/bridges/WaddellGlossary/GlossA.htm>.

Forces and Terms

Compression: A state of being compressed or crushed due to pressure.Tension: A state of being stretched.

Shear: A pulling force to two different directions

Torsion: A twisting in different directions.

Bending: The two opposite sides go in one direction the center goes in the other direction.

"A." Glossary of Bridge Terminology--. Lichtenberger Engineering Library. Web. 28th nov. 2014. <http://sdrc.lib.uiowa.edu/eng/bridges/WaddellGlossary/GlossA.htm>.

Best Bridge TypesTruss

Pros Conso Strong with

tensiono Spreads weight

outo Strong against

bending and torsion

o Weak with compression

o Outer edges could give out point of weakness

o Not strong with compression

Arch Pros Conso Strong with

compressiono Wont bend if

load is on topo The arch can

go under the surface of a bridge and have another bridge on top

o Weak with tension

o The center is weak unless weight is distributed

o Weak with less height in the arch

Beam Pros Conso Strong when

shorto Stands tension

and compression the same

o Simple design

o Weak when long

o Weak by it selfo Will bendo It isn't

designed to fight tension, compression, or torsion force

"Beam." Beam. Web. 30 Nov. 2014. <http://www.warwickallen.com/bridges/BeamBridges.htm>.

"Arch Bridges." Arch Bridges. Web. 2 Dec. 2014. <http://www.design-technology.org/archbridges.htm>.

"Arch Bridges." Arch Bridges. Web. 2 Dec. 2014. <http://www.design-technology.org/archbridges.htm>.

Triangles

Triangles are the most important shape in bridge architecture. This is because the angles of the triangle can’t change with out the length of it’s sides changing. This means the angles won’t change. Triangles are unique since they are the only shape which wont wiggle and change it’s angles. The only way for a triangle to collapse is if the material itself breaks. For this reason we knew we had to use triangles in our design as much as possible."This Site Requires a Modern Browser with Javascript Enabled for Full Functionality." The Strength of Triangles. Web. 9 Dec. 2014. <http://www.mathsinthecity.com/sites/strength-triangles-bloomsbury-tour>.

"Physics of Triangles." Physics Forums. Web. 10 Dec. 2014. <https://www.physicsforums.com/threads/physics-of-triangles.443267/>.

Also using my knowledge and scientific sense I figured that triangles with wider angles will direct the load and force on them to the outer(horizontal) direction and will help distribute weight or direct it away from a pressure point. The exact opposite applies to triangles with smaller angles .

Bridge Design… Arch + Truss

Our design had to be the strongest bridge. We had to use our knowledge from the inquiry stage. Our decision was to combine all three of the bridges (Truss, Beam, Arch).

We chose this design because we saw each bridge had strengths and weaknesses.

E.g.: Arch bridges are strong against tension, and truss bridges are strong against compression.

The two bridges we chose were an arch bridge and a truss bridge (our truss bridge was a beam bridge but stronger).

Part 1:Truss BridgeThe Truss bridge is placed on top. It is mainly strong against tension. The ideal design would be to have it as a triangle. The original Idea was to have the inside frame as a set of triangles on the bottom and a set on top. This was inspired by the Cable Stayed bridge design. This design would fight tension and compression.

In the original design the top was a triangle but the load had to be placed on top and we needed a flat surface not an edge.

The bottom of the truss bridge is basically a beam bridge and this part of the bridge is wider compared to the top. The wider the length is the weaker a beam bridge is so to inforce this the bottom has two layers of popsicle sticks instead of one.

Part 2:Arc Bridge

The Arch would go on the bottom of the bridge just because it is simpler to make. From the bottom it will support the bridge against compression forces. For the Arch to work and not snap in the middle it has to have a high arch so the force and pressure is directed in the vertical direction instead of the horizontal direction (like the triangle). The arch would also need support so the triangles are the answer. In the final design we decided to have the triangles with wide angles in the middle. This was to direct tension and compression away from the center. Closer to the outside the angle of the triangle’s angles would get smaller to direct the force towards the ground/desk.

Final design The final design

evolved from a rough draft, to a blue print, and finally got turned into a 3D popsicle bridge. There were more changes to the design as time went on depending on resources. By the end, the triangles in the arch and truss were not all there because we ran out of sticks. The other part of the design was the sides/bottom/top. The best design is simple X’s since it creates more triangles. The sides in the end are the weakest because they were forgotten about and there wasn't enough sticks to finish the bottom. This might be the shortcoming of the entire bridge.

PlanPerson-Amount done (%)

Task Place to do-resources

Parsa 40% & Eric 60%

Planning sheet-ideas and designs (90min)

Engineering room-school

Parsa Final draft on grid paper (60min)

Home

Parsa 50% & Eric50%

Making Truss Bridge(210min)

Engineering room-school

Parsa Making Arch Bridge(260min)

Engineering room- school, lunch time

Parsa Final Power Point(450min)

Home

Testing and Reflection

Why Our Bridge Failed?Our bridge failed at 25 pounds, but not because it was weak. The bridge didn't even break it basically slipped off the table and remained in one piece on the floor. This was the result of a number of factors:

• The table was smooth• The table was round at the edges• The bridges spam was 33 cm which was barely enough• The force was all directed down in the vertical direction

The top three bullets were the weakening factors, but the main factor was our bridge was designed to direct any energy away from the middle, outwards, then down wards. Although this should have made the bridge stronger it made it easier to fall off the table. In conclusion the factor that was supposed to be the advantage of the bridge turned out to be its down fall… literally.

What would we do differently next time? Next time to improve our bridge’s performance and endurance we should try and stabilize the bottom of the bridge by increasing it’s span. Doing so we will insure that the bridge wont fall off the tables. We would do this by adding some spare pieces of broken popsicles that weren't there before to the bottom. If this plan works, our bridge should hold up a fair amount of weight (50+ pounds). In the second test of our bridges our short coming will probably be the bridge wobbling to one side and breaking sideways.