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The Effect of Bridge Design on Weight Bearing Capacity

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Erik Scow

on 8 May 2014

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Transcript of The Effect of Bridge Design on Weight Bearing Capacity

The Effect of Bridge Design on Weight Bearing Capacity:
Erik Scow

Brief Intro to Bridges
Bridges are as old as nature itself, the first of them being thing such as fallen logs or paths mode up of stones
Materials and designs in bridges help them work
Bridges play a large role in human civilization
Materials Required for the Experiment
Popsicle sticks
90 lb or higher rope
Bucket of sorts
Electronic scale
Step 1: Create/find two stable platforms to put each side of the bridge on.
Step 2: Use something to place weights in (a bucket of sorts) or simply place weights on top of the bridge (won’t work for suspension bridge)
Step 3: Place a small box or book on the top of the bridge and hang the rope holding the bucket from it (skip step if placing weights directly onto the bridges)
Step 4: Add weight until the bridge breaks, Record data every time you test the bridge.
Step 5: Repeat steps for each bridge. Each bridge should be tested the same way.
Scientific Background
What Helps Bridges Work Properly
Materials help determine how much the bridge will hold.
The heavier and more durable the materials, the more it will hold (that is, if they are placed correctly according to the design of the bridge)
Shapes in the design contribute greatly to bridges working properly
Triangles are the strongest shape in construction
On a triangle, the angles cannot be changed. They are stuck in place
The design of the bridge itself also contributes to the working of the bridge, of course
Forces Involved With Bridges
There are forces the fight against bridges
Tension: the same force put on a rubber band when you pull it apart. It affects the underside of the bridge pulling away from each other
Compression: The same force as a spring being pushed together. Is a pushing force that affects the top of the bridge.
Torsion: A twisting wave-like force. Mostly a concern for suspension bridges as some other bridge types' shapes naturally stop it.
There are many other forces involved, but these are the main ones
Bridge Types
Beam Bridges
The oldest and simplest type of bridge
With it's supports on either side, it will withstand compression and tension
One, modern, type of beam bridge is a

A truss bridge spreads force throughout a truss structure, made up of triangles
It is stronger than a regular beam bridge
truss bridge
Arch Bridges
Arch bridges have been in use since Roman times
They are a semi circular shape
Their natural shape directly stops compression and tension.
If built too large, tension will take hold of, and destroy the bridge
Suspension Bridges
With a suspension bridge, cables attached to towers on each side of the bridge hold the bridge up
On each other side of the tower, the cables are anchored to the ground
Towers under compression, being pushed into the ground by the cables on either side
Roadway built on a deck truss to thwart torsion
History of Bridges
The very first bridges were created by nature
Bridges designed by humans have been found in many ancient civilization
Bridges then began to show up in more and more places
The Romans revolutionized bridge building with the invention of the Roman arch
Primitive Africans were the first to build suspension bridges
All bridge types have been influenced by past bridges
The beam bridge had a strength to weight ratio of 2.5 oz (weight) to aprx. 36 lb (strength) or 1 oz (weight) to aprx. 14.4 lb (strength)

The arch bridge had a strength to weight ratio of 2.7 oz (weight) to aprx. 40 lb (strength) or 1 oz (weight) to aprx. 14.8 lb (strength).

The suspension bridge had a strength to weight ratio of 3.5 oz (weight) to aprx. 27 lb or 1 oz (weight) to aprx. 7.7 lb
When I tested each bridge...
Unfortunately, I fear my results are incorrect because...

When I tested the beam bridge, I was unwise to wrap the rope holding the bucket around the bridge.
the rope squeezing the bridge together collapsed it, instead of weight pushing down on it

When I tested the arch bridge, the books I placed on top of it were imbalanced. The books fell from the bridge to the side, causing it to break
When I built the suspension bridge, instead of tying the ends of the paracord to anchorages, I simply tied them to the undersides of the towers. This greatly affected the effectiveness of the bridge. The cables were only attached to one side, causing the towers to fall inward and the bridge to bow and eventually break.
If I could redo this project, I would,
first test all of the bridges correctly and,
second build multiples of each bridge type in case something went wrong in the testing
Work Cited
"Building Strong Shapes with Triangles." Building Strong Shapes with Triangles. Web. 08 Apr. 2014. <http://www.rogersconnection.com/triangles/>.

"Historic Truss Bridges." Historic Truss Bridges. Web. 29 Apr. 2014. <http://www.paprojectpath.org/historic-truss-bridges>.

"History of Bridges." - Tunnels and Bridges History. Web. 29 Apr. 2014. <http://www.historyofbridges.com/>.

"History of Suspension Bridges." Extendedprojectelodie. Web. 29 Apr. 2014. <http://extendedprojectelodie.wordpress.com/2012/11/04/history-of-suspension-bridges/>.

Lamb, Robert, and Michael Morrissey. "How Bridges Work." HowStuffWorks. HowStuffWorks.com, 01 Apr. 2000. Web. 29 Apr. 2014. <http://science.howstuffworks.com/engineering/civil/bridge.htm/printable>.

"Materials Used in Bridges Construction.” Web. 29 Apr. 2014

I will create a beam bridge, an arch bridge and a suspension bridge out of Popsicle stick and test to see which one will have the greatest strength to weight ratio
I believe that the suspension bridge will be the strongest bridge, because it is able to span longer distances, hence forth it may be able to hold more weight.
Beam Bridge
Arch Bridge
Suspension Bridge
Full transcript