AP Physics 1
Bridge Engineering
Research Project
Kevin Souza
29th May, 2020
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Design Theory
Main Idea: ​Triangles are considered to be the strongest shape in structural design and are
therefore considered to be optimal in the designing and constructing of modern bridges.
…………......​Main Idea: ​Triangles can be found everywhere in the framework of a bridge as seen by
the red outlines in the structure
Triangles are used in bridges because they are able to successfully and evenly
distribute weight without changing their proportions. Any added force is spread equally
to each of three sides. Unlike the superior triangle, squares or rectangles would likely be
flattened out with the application of an extensive force. This is why the addition of a
diagonal piece commonly placed across the middle of a rectangle in order to strengthen
its integrity. A common pattern in bridges is the placement of triangles within triangles.
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This repeating pattern allows for the further even distribution of weight, but more
importantly tension in the bridge’s elements.
The connected elements of a bridge, including its joints and members, are
stressed from tension and compression in response to dynamic loads. As stated before
triangles are more suited to deal with these forces than quadrilaterals that are more
susceptible to caving in under intense weight. The type of triangle itself is not as
significant to the sturdiness of a bridge, but certain bridges do utilize certain types of
triangles. Equilateral triangles are most commonly used in truss bridges, while scalene
triangles are more closely associated with suspension bridges. Right triangles are used in
almost all bridges regardless of design.
Caption: ​Labeled diagram of a basic bridge design showing the relevancy of triangles
in the bridge’s framework.
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Bridge Builder 2016 Software
Design #1: ​With the first design that I created using the software, I was more concerned with the
integrity of the bridge itself and making sure that it could withstand the weight of the truck. I
played around with the materials and thickness of members, but ultimately I just tried to
implement as many triangles as possible for sturdiness.
Design #1 Simulation: ​After designing my bridge, I wanted to make sure that it was functional so I
ran it through the simulation and it held up as seen below.
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Design #1 Cost Calculations: ​With the first design, I was not concerned with the cost as long as
the bridge was functional so the total expense came out to approximately $290,000.
Design #2: ​With my second design, I wanted to create a bridge using as little members as
possible to lower the cost, but also make sure that the bridge remained functional. I started away
from the conventional rectangular truss design that I created in attempt #1, and I attempted an
arc. For this bridge I researched ways to make sure that the arc was done properly.
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Design #2 Simulation: ​I ran my second design through the simulation and it held up just like
design #1.
Design #2 Cost: ​I was able to lower the cost to just above $210,000, over 80 thousand dollars
less than my first design attempt.
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History of Truss Bridges
Definition:​ ​A bridge in which the load-bearing structure is composed of a framework that
is a complex composed of connected elements, typically forming triangular units.
Caption:​ ​Example of a truss framework
Prior to the explosion of the industrial revolution in the nineteenth century, the
majority of bridges were constructed from stone. Unbeknownst to architects, wood and
iron are capable of resisting tension more efficiently than the stone counterpart. It wasn’t
until 1820, that Ithiel Town patented the first truss bridge, Town’s lattice truss. While still a
simple variant of the concept, Town’s lattice truss proved to be efficient in material
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demand. Ithiel Truss’ concept for his bridge was built in an era when wood was abundant
in the US and seen as a great replacement for stone in bridge construction. The next
major event in Truss Bridge History came with the patent for the first Iron based truss
bridge in 1841. The patent was birthed by Squire Whipple and resulted in the nation’s
transition from wooden bridges to wrought iron bridges. Iron was then phased out by
steel beginning in the 1880s. Since then then both the design and construction material
have undergone improvements. We have been introduced to material such as quenched
and tempered steel, as well as carbon infused steel. Architectural advancements have
allowed for the success of the truss design for over a century.
The introduction of the truss bridge design allowed for the development of many
variants to the original design. For example, there is a Burr Arch Truss that consists of a
combination o f an arch and truss that provides a strong and rigid bridge design. A Howe
truss has vertical elements and diagonals that slope upwards towards the center of the
bridge. A Pratt truss has vertical members and diagonals that slope downward towards
the center; commonly used for railroad bridges. These are just a handful of truss variants
that have been since developed. The structural design theory allows for many elements
to be altered to suit a desired purpose. An additional truss design that deserves a
mention is the Vierendeel truss, which has members that are not triangular, but instead
rectangular. These rare forms of bridge structures are more expensive than their
triangular counterparts. Once again proving the structural and cost efficiency of a
triangular member-based bridge design.
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Fast forward a century and the Truss design can still be seen in bridges today. The
Francis Scott Key Bridge in Baltimore, Maryland is a perfect example of a truss utilized in
modern day. The bridge spans just over twelve hundred feet since it’s completed
construction in 1977. Another honorable mention is the Astoria-Megler Bridge in Astoria,
Oregon. Originally constructed in 1966, it was considered to be the longest truss bridge
with a span of twelve hundred and thirty-two feet. It maintained its title until the
construction of the Ikitsuki Bridge in 1991. Erected in Nagasaki Prefecture, Japan, the
Ikitsuki Bridge spans thirteen hundred and twelve feet or four hundred meters. Needless
to say, the Truss design has beat the test of time and the three aforementioned bridges
are just a small example of the many truss bridges standing to this date.
Caption:​ ​The Ikitsuki Bridge erected in Nagasaki, Japan in 1991 (1312 feet)
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Suspension Bridges
Definition:​ ​A bridge in which the weight of the deck is supported by vertical cables suspended
from larger cables that run between towers; anchored in abutments at each end of the design.
Caption: ​The Golden Gate Bridge in San Francisco, California (4,200 ft long)
The earliest documented version of a suspension bridge was built by Thangtong Gyalpo
in the fifteenth century. Gyalpo built more than fifty eight iron chain suspension bridges in Tibet
and Bhutan. The last standing bridge constructed by him was destroyed in a flood in 2004. Fast
forward a couple hundred years, and the first iron chain suspension bridge in the US was
constructed in Westmoreland, Pennsylvania in 1801. The bridge was designed by James Finely
and is credited with having all the components of a modern suspension bridge concept. Finley
patented a system for suspending a rigid deck from a bridge’s cables in 1808. Two more bridges
followed, the Dryburgh Abbey Bridge (1817) in England and the Union bridge (1820). The following
major event occurred with the construction of the first large bridge that utilized Finley’s patented
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technique. The bridge extended over the Menai Straits in Wales and was completed in 1826.
This was a huge step for the development of suspension bridges. It wasn’t until 1930 that the
chains used for deck suspension were replaced by cables consisting of many intertwined wires.
This method was introduced by french engineers and then altered by American inventor, John
Roebling. He found a way to intertwine the cables at the site of construction rather than
transporting prefabricated cables. In addition to this contribution, he also invented a rigid deck
platform that was stiffened by trusses, therefore combining two of the most successful bridge
designs of the time.
The most notable contribution of suspension bridges is that they allowed for the bridging
of spaces that could not be connected with older, more conventional methods. They allowed for
longer spans than tradicional truss influences designs. Another advantage of suspension bridges
is that they were cheaper to construct even when covering larger spans. In addition they are
more earthquake resistant than other bridges, as they need limited access to below. They
required less materials and therefore were more efficient for architects. Suspension bridges can
be easily modified to accommodate wider vehicles of additional lanes. Suspension bridges do
come with some notable disadvantages. They need to be constructed either incredibly stiff or
very aerodynamic in order to avoid vibrations produced by high speed winds. The deck can also
support less heavy rail traffic in comparison to other designs.
Notoriously known for their long spans, suspension bridges are extremely abundant in the
world. The longest span suspension bridge to date is the Akashi-Kaikyo Bridge in Japan.
Completed in 1998, the bridge’s central span is just over 1990 meters. The bridge is composed of
six lanes for a combined length of 3,911 meters. The sturdy bridge has been designed to
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withstand winds up to 286 kilometers and earthquakes with a magnitude up to 8.5. The bridge
stands at 298 meters above sea level. Another famous bridge is the Great Belt Bridge in
Denmark. It is also known as the East bridge and it connects Halsskov and Sprogo. It is the
longest suspension bridge outside of Asia with a central span of 1624 meters. Another honorable
mention is the Humber Bridge in the United Kingdom. It has a central span of 1410 meters and is
the seventh longest suspension bridge in the world.
Caption: ​The Akashi-Kaikyo Bridge in Kobe, Japan has the longest running central span for a
suspension bridge to date (1,991 meters long)
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Work Cited
Akanksha. “The World's Longest Suspension Bridges.” ​Verdict Traffic​, 28 Jan. 2020,
www.roadtraffic-technology.com/features/feature-the-worlds-longest-suspension-br
idges/.
Elrod, Jennifer. “Geometric Concepts Found in Bridges.” ​Sciencing,​ 2 Mar. 2019,
sciencing.com/geometric-concepts-found-bridges-8711435.html.
“History of a Truss Bridge.” ​Tennessee State Government - TN.gov​,
www.tn.gov/tdot/structures-/historic-bridges/history-of-a-truss-bridge.html.
Lewis, Scott. “The World's Ten Longest Continuous Truss Bridges.” ​Engineering
NewsRecord RSS,​ Engineering News-Record, 8 Jan. 2016,
www.enr.com/articles/38496-the-worlds-ten-longest-continuous-truss-bridges.
“NCDOT.” ​NCDOT,​
www.ncdot.gov/initiatives-policies/Transportation/bridges/historic-bridges/bridge-ty
pes/Pages/truss.aspx.
Newcomb, Tim. “A Brief History of Bridges From Stone to Suspension.” ​Popular
Mechanics,​ Popular Mechanics, 5 Apr. 2018,
www.popularmechanics.com/technology/infrastructure/g16639655/a-brief-history-o
f-bridges-from-stone-to-suspension/.
The Editors of Encyclopaedia Britannica. “Suspension Bridge.” ​Encyclopædia Britannica,​
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Encyclopædia Britannica, Inc., 15 Nov. 2016,
www.britannica.com/technology/suspension-bridge.
“Triangles & Trusses - Lesson.” ​TeachEngineering.org,​ 2 July 2019,
www.teachengineering.org/lessons/view/cub_trusses_lesson01.
“Why Are Triangles Used in Trusses?” ​Hunker​,
www.hunker.com/12417426/why-are-triangles-used-in-trusses.
“Why Triangles.” ​Bridges,​ trianglesinbridges.weebly.com/why-triangles.html.