8th Grade Toothpick Bridge Building Project
There are more than half a million bridges in the United States, and you rely on them every day to cross
obstacles like streams, valleys, and railroad tracks. But do you know how they work? Or why some
bridges are curved while others are straight? Engineers must consider many things -- like the distance to
be spanned and the types of materials available -- before determining the size, shape, and overall look of
a bridge. Since ancient times, engineers have designed four major types of bridges to withstand all forces
of nature.
Types of Bridges
The beam bridge...
consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The
farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.
Sneak a peek at the forces that act on beam bridges!
Check out other types of beam bridges!
Beam bridge
The truss bridge...
consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel
bars. The Firth of Forth Bridge in Scotland is a cantilever bridge, a complex version of the truss
bridge. Rigid arms extend from both sides of two piers. Diagonal steel tubes, projecting from the top
and bottom of each pier, hold the arms in place. The arms that project toward the middle are only
supported on one side, like really strong diving boards. These "diving boards," called cantilever arms,
support a third, central span.
Cantilever bridge:
Firth of Forth
Check out the forces that act on truss bridges!
The arch bridge...
has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most
arch bridges are made of steel or concrete, and they can span up to 800 feet.
Catch a glimpse of the forces that act on arch bridges!
Check out how arch bridges are built!
Ancient Roman aqueduct
The suspension bridge...
can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges
have a truss system beneath the roadway to resist bending and twisting.
See how forces act on suspension bridges!
Suspension bridge:
Golden Gate Bridge
Check out another type of suspension bridge!
Now that you've mastered the bridge basics, test your bridge-building skills in the Bridge Challenge!
The goal of the competition is to design the strongest possible structure to span at least 9 inches using
only round wooden toothpicks and glue.
OBJECTIVE
To design and build a bridge which can be tested for structural strength and then analyzed for the forces
involved. The structure must span at least 9 inches using only round wooden toothpicks and glue.
You will want to research designs and truly think about how you will construct the bridge. This is a
tedious, time consuming project that requires A LOT of PATIENCE. Drying time will be your worst
enemy in completing this project.
Design Constraints
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Toothpicks (Maximum of 500): Only round wooden toothpicks may be used (square toothpicks
with rounded ends will not be allowed). The toothpicks are to be glued together as they come
from the box. No cutting, splicing, or fraying of the ends is allowed, except:
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The tips of the toothpicks at the top of the structure may be trimmed off to enable the
weights to rest flat on the top
The tips of the toothpicks at the end of the structure may be trimmed to allow the
structure to butt up flush with the supports.
Glue: Only white glue, such as Elmer’s or yellow woodworking glue, such as Titebond, may be
used. Structures built with other glue will be disqualified.
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Coating: Structures may not be painted, sprayed or dipped in any coating or materials
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A roadbed must be a part of the design. (You will note that there is no roadbed in the image at
the top of this project page, but one must be included in your project in order for the experiment
to be conducted) Any design can be used as long as the roadbed is flat and unobstructed.
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The bridge must be free standing and allow for a 1 inch board to pass under the bridge while it
rests on a flat surface.
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Only the materials listed may be used to build the bridge.
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Excessive amounts of glue may not be used as part of the structure, i.e. the bridge may not be
completely covered with glue.
Cardboard/Shoe Box (rectangle for the base of the bridge)
Wax Paper
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INSTRUCTIONS
Each student will research bridge designs from the Internet or analyze actual structures, noting materials
used, bracing points and reinforcements, and how each design takes into account. Each bridge will be
judged for its strength and its aesthetic qualities.
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Judging of the aesthetic design of the bridge will consider neatness and uniqueness of the
finished bridge.
Strength will be tested by placing a steel rod across the middle of the bridge, a chain will be
placed on both ends of the rod and attached to a 5 gallon bucket.
All weights will be placed in the bucket.
When the bridge breaks, the weight prior to its breaking will be recorded on the Bridge Weight
Chart.
The bridge that held the most weight, after all bridges have been broken will be the winner.
Write three paragraph essay to accompany each of the bridges that should explain :
Type of bridge they built
The reasons they chose that particular style of bridge.
Any conjectures on architecture that makes the strength and durability of a bridge successful or
unsuccessful.
Steps that that you took to build a bridge.
Analyze any problems and how they were resolved.
Make generalizations about the strength of the bridge based on research.
Assume the toothpick bridge is a scale model of an actual bridge with the length of 1000 feet.
Determine the scale of the model bridge.
Grade: Each day you will begin with a grade of 100 for adhering to ALL classroom guidelines. T any
time you are not complying with the rules and the teachers has to address your behavior; 20 points will
be deducted from the days’ grade. These grades will count as a quiz grades. At the end of the project
you will receive two test grades one for the written essay and one for the bridge.
Grades Eighth - Mathematics Content Standards.
The geometry skills and concepts developed in this discipline are useful to all students. Aside from
learning these skills and concepts, students will develop their ability to construct formal, logical
arguments and proofs in geometric settings and problems.
Goal #2: The learner will understand and use measurement concepts.
2.01 Students know, derive, and solve problems involving the perimeter, circumference, area, volume,
lateral area, and surface area of common geometric figures.
2.01 Students compute the volumes and surface areas of prisms, pyramids, cylinders, cones, and spheres;
and students commit to memory the formulas for prisms, pyramids, and cylinders.
2.01 Students compute areas of polygons, including rectangles, scalene triangles, equilateral triangles,
rhombi, parallelograms, and trapezoids.
2.01 Students determine how changes in dimensions affect the perimeter, area, and volume of common
geometric figures and solids.
Goal #3: The learner will understand and use properties and relationships in geometry.
3.01 Students prove that triangles are congruent or similar, and they are able to use the concept of
corresponding parts of congruent triangles.
3.02 Students prove the Pythagorean Theorem.
3.02 Students use the Pythagorean Theorem to determine distance and find missing lengths of sides of
right triangles.
3.02 Students know and are able to use angle and side relationships in problems with special right
triangles, such as 30°, 60°, and 90° triangles and 45°, 45°, and 90° triangles.
3.03 Students know the effect of rigid motions on figures in the coordinate plane and space, including
rotations, translations, and reflections.
8th Grade Mathematics: Toothpick Project Assignment
Student’s Name___________________________________________________________
Math Teacher’s Name_____________________________________________________
Deduction#
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Final Daily
Grade
Date
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Final
Average
Essay Grade
Bridge Final
Grade
Comments:
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