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Building a Bridge

Formal Lab Report

By

Ladji Timite

Physics Mr.Jonathan

Ellis Preparatory Academy January 16, 2015

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Ladji Timite Physics December 2014

Introduction

My thesis is that a Suspension Bridge is well suited to build for crossing the Hudson

River in the New Paltz area. The purpose of my project is to create a bridge that is most

suitable to cross the Hudson River near New Paltz, New York. I am designing this bridge to ease

congestion in the area, also create a pathway that make it easier to cross the Hudson river, and

help the traveling in that location save time by traveling from one side to the other side of the

Hudson River. In this project we will be talking about two main forces that are apply on our

bridge. Compression is a pushing force that pushes from both end of an object, causing it to

contract on itself. Tension is a pulling force that pulls an object from both end, causing a level of

strain depending on how much the object is being pull.

Some geographic features in the area, New Paltz near Hudson river, is that the area has

high cliffs which makes it difficult to build bridges just on the Hudson river, but instead all the

way over the cliff, making the bridges longer. Some historical facts about the village of New

Paltz is that it was founded in 1678 by French Huguenots who had taken refuge in Mannheim,

Germany, for a few years before coming to America because of the war. (Welcome to Village of

New Paltz.) Also there is a Suspension Bridge name Mid­Hudson bridge open august 25, 1930,

the length of the bridge is 910m and was made to make it easier to cross the long river to the

other side of Hudson River. (Mid­Hudson Bridge.) The actual length of our bridge is 727m long;

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we found it by searching the location on Google Maps, and then measured the width of the

Hudson River using the scale factor of the site. The scale factor was 2.2 cm correspond to 500

Ft., which when we calculate it was 2386.36 Ft. Then cover it into meters which is 727.36 m.

The different types of bridges that I could have chosen for my project were an arch Bridge, a

Truss bridge, and a suspension bridge. The similarities between the suspension bridge and truss

bridge is that they both can be built for a long distance purpose. Also, both have tension and

compression forces applying on them, but suspension bridges are not made for windy areas,

which can be recall of the Tacoma Narrows Bridge. This bridge was self existed because of the

change of pressure cause by the wind, making it twisted on itself and collapse. ( Introduction

UW Libraries). Arch bridge are usually not made for long spans, is its curved design, which does

not push load forces straight down, but instead they are conveyed along the curve of the arch to

the supports on each end. These supports carry the load of entire bridge and are responsible for

holding the arch in the precise position unmoving position. "Arch Bridge ­ Types of Arch

Bridges." Arch Bridges. Suspension Bridge is to be more appealing to the public while the truss

is made to withstand heavy payload. My decision of picking the suspension bridge is the best

because it covers the long area need to cross the Hudson river, during the year there is not that

high of wing. Thus the platform will not be unstable because of high wind like the Tacoma

Narrow Bridge. In final it need to be appealing to attract visitors and will help the economy of

New Paltz.

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1. Experimental Design

By building our model bridge, it will give us evidence to demonstrate that it a suitable

bridge for the Hudson River near New Paltz. By being able to reach a certain length that should

be equivalent to the width of the Hudson River. Second, it has to be able to withstand a certain

amount of payload; in addition the platform must be at a definite width, towers height, the height

between the platform and the river, and all using 10 manila folders to make it. Those requirement

where:

A. The Suspension bridges must be at least 40 cm between their pillar supports.

B. The bridge platform must be at least 10 cm wide.

C. The bridge platform or its structure must be at least 15 cm above the table.

D. Finally, the finished bridge must be able to support a total weight of 45 Newtons (4.588

Kg)

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The plan on building a suspension bridge, specifically a cable­stayed bridge with the

length of 2500m with a span of 1500 m, and a tower with a height of 100 m. For the model we

planned to use ten manila folders and strings of the cables, and for the real bridge of course we

will use some type of metal and steel to build it. Some variable we could have change are the

material we used to build our models, like instead of making it with manila folders we could

have used cardboard or popsicle sticks. This will help us have a better understanding of the

solidity of the bridge and a clear view of forces acting on it like tension, shear, and compression.

Also raise the amount of weight, to be comparable to the real weight applied to a real bridge. We

found information to help build our bridge by doing an experiment. Its purpose was to research

how the thickness of the platform on a bridge helps hold heavy payloads. We used manila folders

to make the deck, as well as to tape each end on a desk and adding the way on it. The way we

calculated it was, for each time we add a new platform on top of the old ones, we see how much

deflection it reduces compared to a single platform. At the end of the experiment we found that

the minimum amount of thickness on the bridge, was 10 manila folders to hold 45 newtons of

weight. Additionally, we used website link on www.ellisprepphysics.blogspot.com that Mr.

Jonathan made to understand our bridges and how to build it. The steps we have taking in

building our bridge was to build our towers first, because we thought that it was the most

difficult task in building our model bridge. My partners designed the tower with some paper and

we discussed the good and bad about it, then we started to build them each out of two manila

folders. Secondly, we started to build the deck with the information we got from our experiment,

which is increasing the thickness of the deck with six rectangular shapes cut out of the manila

folders. Finally adding the cable of the suspension bridge, in which we use strings that go on top

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of tower and through two holes in the platform in each side. Some bias we had was that if we

added columns or a truss bridge structure in the towers, it would make it even stronger, and

prevent the whole bridge from binding to one side, also if we have more materials (manila

folders) it would have been completed.The actual length of our bridge is 762 meters long; I

calculated with the ration in Google map the width of the Hudson River, which is 2 cm, is equal

500 feet. Therefore I measure the width of the Hudson River which was 10 cm,

. Then convert it into meter which is 727.36 m. "Google Maps."Google 386.36 ft2.2 cm10 cm ×500 f t = 2

Maps. N.p., n.d. Web. 30 Dec. 2014.

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2. Data

Y= mean deflection R2= The equation in that graph R2= 0.94399 represent how accurate the information in the graph is, the closer it is to one, the more reliable those information are.

Class Average Data

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The deflection of the manilla folder

Number

of folders

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Average

1 1.5 cm 2.8 1.4 1.1 2 2.2 1.8

2 1cm 2.4 1.2 0.9 1.5 2 1.5

3 1 cm 1.9 1.3 0.8 1 1.8 1.3

4 1.2 cm 1.6 1.3 0.5 1 1.5 1.1

5 1.1 cm 1.4 1.2 0.5 1.1 1.3 1.1

6 1 cm 1.2 1.5 0.4 1 1.1 1.0

7 1 cm 1.1 1,.4 1 0.9 1 1.0

8 1.1 cm 1.0 1.3 1.1 1.1 0.8 1.0

9 0.9 cm 0.8 1.3 1.3 1.1 0.6 1

10 1 cm 0.6 1.2 1 1 0.4 0.8

In the final analysis our bridge was able to hold a weight of 45 newton, however the

support were binding. This mean that my group need to make a stronger tower by changing the

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design in order to distribute the compression force that apply on it through the cables. Also the

deck were binding in the middle, no because of the thickness of the bridge, but because there

wasn’t much support from the cables. We only made two holes in each side of the bridge,

specifically in the middle of bridge. This creates too much tension for the strings to hold and also

lead to a greater amount of compression in the tower, another reason why the towers were

binding. For that we need to make more holes along the bridge to distribute the forces evenly.

3. Analysis

Based on my results, I still think that our bridge is the most suitable bridge, even though

the deck bended from the weight. First because of the Mid­Hudson that was build in the area

next to where I plan to build my bridge, this show that the suspension bridge is a logical choice

to be build there. Also according to the number of folder and class average graph seen

previously, we should have use a 10 manila folders for the deck, but with the limited materials

we only use 6 instead. The equation in that graph R2= 0.94399 represent how accurate the

information in the graph is, the closer it is to one, the more reliable the information. For this

reason using 10 manila folders would have been the logical choice to hold 45 newtons, but the

limited material would not allow us. Therefore we used six folders to build our platform. Also

there was not much support from the cable to distribute the weight around the bridge, and this

was the reason why our bridge had much deflection in the middle of the deck, but did not fail. In

addition, our towers were not well structure to hold the weight of 45 newton. Thus for the next

model we should use 10 manila folder instead of 6 for the platform, create more cable support

the deck, and make stronger towers.

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This connected to our background research about forces that are apply on a suspension

bridge, meaning that my group need to make a stronger tower by changing the design in order to

distribute the compression force that apply on it through the cables. Also the deck were binding

in the middle, no because of the thickness of the bridge, but because there wasn’t much support

from the cables. We only made two holes in each side of the bridge, specifically in the middle of

bridge. This creates too much tension for the strings to hold and also lead to a greater amount of

compression in the tower, another reason why the towers were binding. For that we need to make

more holes along the bridge to distribute the forces evenly.

4. Revisions

Something that I will change to minimize the experimental errors and effect of bias are

the structure of the Towers. If possible our group will change the hollow towers with solid and

heavy ones that will make it strong and stable. In other words it will prevent the tower from

binding and make it unwavering, also keep the deck from falling out of the towers. Another

change that I would suggest my group to do is add multiple cable supports from each side and

along the way of the bridge. This will make the deck more steady and hopefully not bind while

under a certain weight. Furthermore, this would spread the force of tension in the multiple cables

and convert it to compression on the solids Tower to withstand. In addition, a variable we could

have change are the material we used to build our models, like instead of making it with manila

folders we could have use cardboard or popsicle sticks instead to make more realistic, and get

better data from it.

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A new question that I have about designing bridges is by adding more cables support on

the deck, will it apply less compression forces to the Towers or not? Another question I have is,

how can I implant a truss bridge structure to my towers in order to strengthen and steady them?

Those question are important because they will provide useful information to use in the next

model that my group might make if we get the chance to.

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Bibliography

"Welcome to Village of New Paltz." Http://www.newpaltzvillage.org/home/. Copyright © 2014

The Village Of New Paltz, n.d. Web. 17 Dec. 2014.

Mid­Hudson Bridge (US 44 and NY 55)." Mid­Hudson Bridge (US 44 and NY 55). N.p., n.d.

Web. 17 Dec. 2014.

Arch Bridges. Copyright© History of Bridges, n.d. Web. 18 Dec. 2014

<http://www.historyofbridges.com/facts­about­bridges/arch­bridges/>.

"Introduction." ­ UW Libraries. N.p., n.d. Web. 13 Jan. 2015.

<http://www.lib.washington.edu/specialcollections/collections/exhibits/tnb>.

"Google Maps." Google Maps. N.p., n.d. Web. 30 Dec. 2014.

<https://www.google.com/maps/place/New+Paltz,+NY+12561/@41.75103,­74.0396433,12z/d

ata=!4m2!3m1!1s0x89dd1884bdee8f8d:0x82c17e4b65e32b6f?hl=en>