Overview of the Learning Activities
The five learning activities are as follows:
Learning Activity #1: Build a model of a truss bridge. In this
activity, we will build a model bridge from cardboard ﬁle
folders. The bridge has already been designed, and
accurate drawings and fabrication instructions are pro-
vided. Through this activity, students will learn bridge
terminology, construction techniques, and some basic
concepts in physics and structural engineering. Students
do not need any special knowledge of math or science to
do this activity.
Learning Activity #2: Test the strength of structural members. In
this activity, we will use experimental testing to determine
the strength of structural members made of ﬁle folder
cardboard—the same stuff we used to build our bridge
model in Learning Activity #1. The data obtained from
these tests will be used extensively in Learning Activities
#3 and #5. Students will learn some basic concepts from
engineering mechanics, as well as procedures for design-
ing and conducting experiments. To do this activity,
students need only basic arithmetic skills and the ability
to create a graph. The ability to use a spreadsheet pro-
gram is helpful but not required. This activity requires
the use of a simple wooden testing device. Instructions
for building the device are included in Appendix C.
Learning Activity #3: Analyze and evaluate a truss. Here we will
calculate the internal member forces in our model truss
bridge. We will then evaluate the structural safety of the
truss by comparing these calculated forces to the member
strengths we determined experimentally in Learning
Activity #2. Through this activity, students will learn more
advanced concepts from physics and engineering
mechanics. Students need to apply geometry, algebra,
and trigonometry to do the activity successfully. A review
of key concepts from trigonometry is included; however,
students who have not yet learned geometry or algebra
will not be able to do this project.
Learning Activity #4: Design a truss bridge with a computer. In
this activity, we will design a full-scale highway truss
bridge using the West Point Bridge Designer software.
The design process includes working through multiple
iterations to ensure that the structure will carry the
prescribed loads safely and at minimum cost. Through
this activity, students will learn the engineering design
process and will have an opportunity to reinforce many of
the basic structural engineering concepts learned in
earlier activities. This activity also includes an overview of
how actual bridges are designed and built. Students do
not need any special knowledge of math or science to use
the West Point Bridge Designer.
At ﬁrst glance, cardboard from
manila ﬁle folders might seem an
odd material to use for bridge-
building projects. But in fact, I
have found it to be far superior to
the more traditional model bridge-
building materials—balsa wood,
popsicle sticks, toothpicks, and
File folders are readily available and very
Cardboard is easy to work with. It can be
easily folded, cut with a scissors, and glued
with common household adhesives.
The behavior of cardboard as a structural
material is surprisingly predictable.
Cardboard provides the capability to build
two fundamentally different kinds of
structural members—hollow tubes and
solid bars. Understanding how these two
types of members work is an important
part of understanding structural
Cardboard provides the capability to build
connections that are stronger than the
members they join together. I can’t
overstate the importance of this char-
acteristic. Throughout this book, we will
learn how to design structural members so
that they are strong enough to carry load
safely. But a well-designed member is of
little use if its connections fail before the
member itself does. A chain is only as
strong as its weakest link. If you’ve ever
built and tested a truss bridge made of
balsa wood or Popsicle sticks, you know
that these structures almost always fail at
the connections. As a result, their load-
carrying capacity is less than it could be
and, more importantly, is almost impos-
sible to predict analytically.
So head for the supply closet; grab
a stack of ﬁle folders; and let’s
build some bridges.
Learning Activity #5: Design and build a model truss bridge. Here we will apply what we have learned in the
previous four activities to design, build, and test a model truss bridge. Students should have completed
Learning Activities #1, #2, and #3 to do this project successfully; however, if they do not have adequate math
background to complete Learning Activity #3, they can bypass the mathematical structural analysis by using
the Gallery of Structural Analysis Results provided in Appendix B. The gallery presents a complete set of
computed analysis results for a variety of different truss conﬁgurations.
A Gallery of Truss Bridges—a compendium of photographs showing actual truss bridges from all over the
United States—is also provided in Appendix A. The gallery is used as part of several learning activities and is
also intended to provide students with a resource for ideas about their own bridge designs.
Also included is a Glossary (Appendix D), which provides deﬁnitions for mathematical, scientiﬁc, and
engineering terms used throughout the book. The ﬁrst appearance of any Glossary term in the text is high-
lighted in bold type.
Organization of Each Activity
This book is organized in a problem-based learning format. Each learning activity is presented as a problem
to be solved. Information pertinent to the problem solution is provided “just in time”—mathematical, scientiﬁc,
and technological concepts are included within the speciﬁc learning activities in which they are applied. Each
activity has a set of learning objectives, which students achieve by (1) working through the problem solution
and (2) answering questions that are intended to stimulate critical thought about key concepts.
Each learning activity is organized into the following sections:
Overview of the Activity. This section provides a brief description of the learning activity.
Why? This section explains why the activity is worth doing and how it relates to previous and subsequent
Learning Objectives. This section lists the speciﬁc knowledge and skills that students can be expected to
gain from thoughtful completion of the activity.
Information. This section provides background information pertinent to the activity. In most cases, stu-
dents would probably be able to complete the activity successfully without this information; however, it is
unlikely that they will really learn from the activity without the context that this information provides. For
example, a student can certainly build a model bridge without understanding the terms tension and com-
pression; however, it is highly unlikely that the student will really learn anything meaningful about how
structures are designed without some appreciation for these terms.
The Problem. This section presents a ﬁctitious scenario describing a need and the student’s role in devising
a solution that satisﬁes the need.
The Solution. This section guides the student through the planning and conduct of the problem solution,
step by step. At appropriate points throughout the solution, questions are posed, as a means of stimulating
critical thinking about important aspects of the project.
Answers to the Questions. Here answers to the critical thinking questions from the preceding section are
provided. This section always starts on a new page, so that the teacher can conveniently provide students
with copies of the preceding six sections, without revealing the answers to the critical thinking questions.
Ideas for Enhancing the Activity. This ﬁnal section provides suggestions for enriching or extending the
students’ learning experience in the activity.
Of these eight sections, the ﬁrst six should be provided to the students to guide their participation in the
learning activity. The seventh—Answers to the Questions—can be provided to students at the end of the
activity, if the teacher chooses to do so. The eighth section is intended solely for the teacher.
Some Simpler Bridge-Building Activities
For the teacher who would prefer to do simpler, more qualitative structural engineering activities, there are
a number of excellent references available. These include:
Johmann, Carol A. and Elizabeth J. Rieth. Bridges! Amazing Structures to Design, Build, and Test.
Charlotte, Vermont: Williamson Publishing, 1999. (For ages 7-14.)
Kaner, Etta. Bridges. Toronto: Kids Can Press, 1997. (For ages 8-12.)
Pollard, Jeanne. Building Toothpick Bridges. Palo Alto: Dale Seymour Publications, 1985. (For ages 5-8.)
Salvadori, Mario. The Art of Construction. Chicago: Chicago Review Press, 1990. (For ages 10 and up.)
WGBH Educational Foundation. Building Big Activity Guide. Boston: WGBH Educational Foundation, 2000.
I am deeply indebted to many people for their invaluable contributions to this book. Colonel Kip Nygren,
Head of the Department of Civil and Mechanical Engineering at the U. S. Military Academy, ﬁrst suggested that
a book of learning activities might be an appropriate way to reinforce the educational value of the West Point
Bridge Designer software. Mr. Brian Brenner, Dr. Mark Evans, and a team of civil engineers from Parsons Brinck-
erhoff provided invaluable input to the description of bridge design in Learning Activity #4. Ms. Cathy Bale
reviewed the manuscript, provided insightful recommendations for improvement, and did the myriad coordina-
tion tasks necessary to get the book into production. The American Society of Civil Engineers (ASCE) provided
funding to support the development of the book, and ASCE’s Managing Director of Education, Dr. Tom Lenox,
was a constant source of guidance, encouragement, and feedback throughout the project. While the book was
still being written, Dr. Doug Schmucker used draft versions of Learning Activities #1 and #2 as the basis for a
project in his Materials Engineering course at Valparaiso University. Doug and his students provided thoughtful
feedback about the book at a very critical time in its development. Many of the photographs in Learning
Activity #1 were taken by Mr. Mike Doyle. Finally, the bridge photographs used for each chapter heading were
provided by Mr. Jet Lowe of the National Park Service.
Colonel Stephen J. Ressler
West Point, New York
VB.NET PDF - Convert PDF with VB.NET WPF PDF Viewer
Files; Split PDF Document; Remove Password from PDF; Change PDF Permission Settings. file formats with high quality, support converting PDF to PNG, JPG, BMP and convert online pdf to jpg; change pdf to jpg online
Overview of the Activity
In this learning activity, you will build a model truss bridge that has already been designed for you. When
construction is complete, you will load the bridge to determine if it performs as its designer intended. With the
load in place, you will be able to observe how the structure works—how the various structural members work
together to carry the load safely and efﬁciently. And at the end of the project, you will save the model as evi-
dence of your bridge-building skill. Don’t break it! We will be using it again in subsequent learning activities.
Design is the essence of engineering. The only way to truly appreciate the challenges and rewards of
engineering is to actively engage in the creative process of design. So why, in this learning activity, will we
devote considerable effort to building a bridge that has already been designed by someone else? It is true that
building an existing design will not allow you to exercise a lot of creativity; nonetheless, this activity will provide
you with valuable preparation for learning how to design a structure. Building an existing design will allow
Learn many key concepts about trusses and structural behavior that you’ll use when you design your own
bridge in Learning Activity #5.
Familiarize with the engineering characteristics of a rather unique building material—cardboard from a
manila ﬁle folder.
Learn some special construction techniques appropriate for this material.
Work with conﬁdence, knowing that your bridge will carry the prescribed loading successfully, as long as
you build the structure with care.
Learn about the challenges faced by real-world construction contractors, who are often required to build
structures that have been designed by someone else.
As a result of this learning activity, you will be able to do the following:
Explain what a truss is.
Identify the major components of a truss bridge.
Identify the types of truss bridges.
Explain the following fundamental structural engineering concepts: force, load, reaction, equilibrium,
tension, compression, and strength.
Explain how a truss bridge works—how each individual component contributes to the ability of the entire
structure to carry a load.
Explain the roles of the four key players in the design-construction process—the Owner, the Design
Professional, the Constructor, and the Project Manager.
Explain how construction quality affects the performance of a structure.
1. Component Parts of a Truss Bridge
What is a Truss?
A truss is a structure composed of members connected together to form a rigid framework. Members are
the load-carrying components of a structure. In most trusses, members are arranged in interconnected tri-
angles, as shown below. Because of this conﬁguration, truss members carry load primarily in tension and
compression. (We’ll discuss these terms in Section 3 below.) Because trusses are very strong for their weight,
they are often used to span long distances. They have been used extensively in bridges since the early 19
century; however, truss bridges have become somewhat less common in recent years. Today trusses are often
used in the roofs of buildings and stadiums, in towers, construction cranes, and many similar structures and
Trusses, like all structures, are designed by civil engineers with special expertise in structural analysis and
design. These men and women are called structural engineers.
The major components of a typical truss bridge are illustrated in the two diagrams below. The elevation
view shows the bridge from the side. The isometric view is a three-dimensional representation of the structure.
Note that certain members are only visible in the isometric view.
A typical truss bridge. Note that the structure is composed entirely of interconnected triangles.
Top Lateral Bracing
End Floor Beam
Component parts of a typical truss bridge - Elevation View
Component parts of a typical truss bridge - Isometric View
The three-dimensional bridge structure has two main load-carrying trusses. Each truss is composed of a top
chord, a bottom chord, and several verticals and diagonals. The two trusses are connected together by a series
of transverse members—struts, lateral bracing, and ﬂoor beams.
In early truss bridges, all of these members would have been made of wood or iron. Today they are usually
made of steel. Modern steel truss members are manufactured in a wide variety of shapes and sizes. A few
common examples are shown on the following page. The model truss we will be building uses both solid bars
and hollow tubes. When we load-test our model, we’ll see why one truss often uses two different types
Based on “Truss Identiﬁcation: Nomenclature,” Historic American Engineering Record HAER T1-1,
National Park Service, 1976.
Types of steel truss members.
One major component of a truss bridge that is usually not made of steel is the deck—the ﬂat surface
between the two main trusses. (In the isometric drawing, only part of the deck is shown, so the structural
members below it can be seen.) Bridge decks are usually made of concrete, but might also be built from
wooden planks or steel grating. When vehicles or pedestrians cross a bridge, their weight is directly supported
by the deck. The deck, in turn, is supported on the ﬂoor beams. The ﬂoor beams transmit the weight of the
vehicles and pedestrians (and the weight of the deck) to the main trusses.
The truss drawings above do not show the connections that are used to join the structural members
together. Even though the connections are not shown, they are important! They have a big inﬂuence on the
ability of a structure to carry load. Indeed, inadequately designed connections have been the cause of several
catastrophic structural failures in the U.S.
There are two common types of structural connections used in trusses—pinned connections and gusset
plate connections. Examples of each are shown in the photographs below. As the name suggests, the pinned
connection uses a single large metal pin to connect two or more members together, much like the pin in a door
hinge. In a gusset plate connection, members are joined together by one or two heavy metal gusset plates,
which are attached to the individual members with rivets, bolts, or welds. Pinned connections were used
extensively throughout the 19
century. Most modern bridges—including the model bridge we will be building
here—use gusset plate connections.
Each of the bridge components described above has a speciﬁc purpose. All of the components work
together to ensure that the bridge carries load safely and efﬁciently. In this learning activity, we will fabricate
and assemble these various types of structural members and components, and we will observe how each one
Typical gusset plate connection
Typical pinned connection.
For more information on structural failures, see Why Buildings Fall Down, by Mario Savadori.
Documents you may be interested
Documents you may be interested