Truss Bridge Design Innovator’s Notebook - Squarespace · Truss Bridge Design Innovator’s Notebook ... Truss Bridge Design | 2 Project ... and you will be challenged to design

• A DIVISION OF •

Truss Bridge Design

Innovator’s Notebook

Prepared by:

Polar 3D

Student’s Name: _________________________________

Teacher’s Name: _________________________________

Truss Bridge Design | 1

Table of Contents

ProjectDesignBrief.....................................................................................................2CourseOverview..................................................................................................................3

TheDesignProcess....................................................................................................................................3Evaluation..................................................................................................................................................3Documentation.........................................................................................................................................4

TheDesignProcess......................................................................................................5DefinetheProblem..............................................................................................................7

SettheStage.............................................................................................................................................7IdentifytheProblem...............................................................................................................................16IdentifytheCriteria&Constraints..........................................................................................................19Discuss&Guide.......................................................................................................................................21Research&Explore.................................................................................................................................23DevelopaSolution.............................................................................................................27

IdeaGeneration......................................................................................................................................27Debate&Decide.....................................................................................................................................32Model&Prototype..................................................................................................................................35Justify......................................................................................................................................................353DPrint(1/2)...........................................................................................................................................35TesttheDesign..................................................................................................................36

TestSetup................................................................................................................................................36Analyze&Communicate.........................................................................................................................37Self&GroupEvaluation..........................................................................................................................39ImprovetheDesign............................................................................................................40

Redesign&Model...................................................................................................................................40Defend.....................................................................................................................................................403DPrint(2/2)...........................................................................................................................................41FinalBridgeCompetition.........................................................................................................................41Write&Wrap-Up....................................................................................................................................41

Evaluation..................................................................................................................43Bibliography...............................................................................................................44


Project Design Brief

Project Name Truss Bridge Design

Authored By Dr. David Thornburg, Ph. D., David A. Parrott, MDes

Subject Area(s) Physical Science, Engineering, Mathematics

Main Grade Level High School (9-12)

Design Software BlocksCAD

Design Time 1 hour

Print Time 1 hour

Tools Caliper for measuring the diameter of the skewers, glue gun, dental picks

Extra Materials Bamboo skewers, weight sets (optional)

Standards Disciplinary Core Ideas: Physical Sciences

Crosscutting concepts: Mathematics

NGSS Standards related to this activity:

K-PS2-1 Motion and Stability: Forces and Interactions K-2-ETS1-2 Engineering Design MS-PS2 Motion and Stability: Forces and Interactions HS-PS2 Motion and Stability: Forces and Interactions K.Forces and Interactions: Pushes and Pulls MS.Forces and Interactions HS.Forces and Interactions

STEAMtrax URL: build.steamtrax.com

STEAMtrax User Name: _________________________

STEAMtrax Password: _________________________


Course Overview

During the course of this project, you and your team will be challenged to

design a model truss bridge. You will be provided with certain resources (e.g. calipers,

dowels, etc.), and you will be challenged to design a proof-of-concept prototype of a

truss bridge and then improve its performance by designing, prototyping and testing new

geometries using the Engineering Design Process described below.

The Design Process

Your project will follow the STEAMtraxPLUS Engineering Design Process. This is

a powerful, iterative process for problem solving. Many versions of this process are used

in the professional world to solve complex challenges in every industry, including New

Product Development (NPD), process improvement, and many others. Examples of these

include the Phase Gate Model, Stage-Gate, User-Centered Design, IDEO’s Design

Thinking, Agile Development, Systems Engineering, Knowledge-Based Development,

Spiral Development, and many, many others. New and improved models for this process

are being developed and tested every day. The process outlined in STEAMtraxPLUS is a

distillation of these processed meant to familiarize you with the rudiments of this

powerful problem-solving methodology.

During the course of this and other STEAMtrax modules, you will work

collaboratively with other team members to define the problem you intend to solve,

develop a solution, test your Design, and improve your Design.

Evaluation

Just like in the real world, this project is self-directed and collaborative. You and

your team will be working collaboratively toward a goal — checking in with your

instructor for review and guidance. In addition to these frequent check-ins, this project

includes four discrete check-in points during which you will be presenting your work

using a number of methods — verbal and written. These include two informal verbal

presentations: Justify (Phase 2) and Defend (Phase 4). There are two short written reports

due in phases 3 & 4. You and your group will be performing self-evaluations following

each written report. Your instructor will evaluate your performance at the end of the

project.


Documentation

Whether its science, mathematics, engineering or design, in the technical fields

documentation is everything. Good documentation is critical to the advancement of

science and industry, because without it, there is no proof of your solution — nor will it be

repeatable. “In a research environment, good research records are essential for a

number of reasons—including for assisting the institution in meeting its progress-

reporting requirements to research sponsors, for documenting expenditures, and for

promoting research integrity.”

In the innovation space, the need for documentation is perhaps even more

important for the inventor, because in “the United States, unlike virtually every other

country, priority of invention is established by the first-to-invent rule… To comply with

patent law, the first party to conceive a patentable invention must carry out certain

activities to proceed with reasonable diligence toward the development and patenting of

an invention… Therefore, an inability to prove who is the first to conceive, or a lack of

evidence to refute a charge that an inventor was not diligent in pursuing an invention,

can lead to the loss of valuable patent rights to which the inventor and institution may

otherwise have been entitled.” (Crowell)

At every step of this project, you will be documenting your findings using this

Innovator’s Notebook. This is intended to introduce you to the habit of documenting all

of your ideas and thought processes as you move through every step of your project.


The Design Process

Design is an iterative process involving research & exploration, innovation &

execution, testing & analysis and documentation. It is rare for a concept to be turned into

a working project on the first try. Most projects require several loops of this iterative

process — each generating enhancements that move the project closer to its goal. This

project and all STEAMtraxPLUS modules follow a distilled version of this iterative

problem-solving process, as outlined on the following page.

The design process is based on constraints. The very act of design reflects a

creative friction between creative options and constraints. For example, there are many

ways to design a simple device, like a hinge. The strength requirements of every part are

a few constraints; cost is another one; as might be the ease of manufacturing. Designing

without constraints is a lot like playing tennis without a net. Sure, you might get the ball

to the other side, but the addition of a net raises the skill required and suits the design to

its context and purpose. Without constraints, a project has no purpose and the designer

has no metric against which to measure the performance of his/her design.

Elegance is another important factor in design. While the American architect Louis

Sullivan famously said that “Form ever follows function,” this principle grew from a core

idea first expressed by Marcus Vitruvius Pollio, the Roman architect, engineer, and

author. Pollio first asserted in his book, De Architectura, that a structure must exhibit the

three qualities of firmitas, utilitas, venustas ― that is, it must be solid, useful, and

beautiful. Just because a design is functional does not mean it can't also be elegant. We

all have visceral reactions to designs ― even if we aren't aware of them. You might be

attracted to one design, while others prefer something different. There are some kinds of

designs that are appealing to a large number of people ― designs based on the Golden

Mean, for example, which show up in everything from ancient Greek temples to the

design of Apple's laptop computers.

As this design project unfolds, consider how you might leverage the powerful

problem-solving methodology outlined below to create a functional and elegant solution

within the constraints of the design challenge.



Define the Problem

Set the Stage

A bridge is simply a structure intended to span an obstacle. A bridge can be as

simple as a log crossing a stream or as innovative as the Gateshead Millenium Bridge, a

mechanized, tilting bridge over the River Tyne.

In nearly all cases, however, bridges are some of the most beautiful and elegant

structures created by man. Because they must support their own weight in addition to

their designed load (traffic, wind, et al.), bridges meant for large spans are necessarily

created to be as efficient as possible. The result is a fusion of form and function in which

materials, construction and form must all be balanced cleverly in the mind of the designer

to create a structure that is more than the sum of its parts. When done beautifully, the

results include world-renowned bridges like the Golden Gate Bridge, the Millau Viaduct,

or the Alcántara Bridge. Though these designs span centuries, all are iconic for their

combination of beauty and utility.

This project focuses on a specific kind of bridge ― the truss bridge ― often used

for fairly short spans carrying heavy loads like trains. The truss bridge represents a

unique structural solution that combines simplicity of design and economy of material in

a way that prior bridge designs did not. Before we explore the truss bridge, let’s take a

look at other types of bridge to see how engineers use basic geometric principles to

span distances — large and small — with bridges.


Types of Bridges

What follows is a short description of a number of general bridge types, including:

beam, arch, cantilever, suspension, cable-stayed and truss. There are many more types

of bridge and many that are hybrids of several of the types mentioned below.

Beam

A beam bridge is the simplest form of

bridge. It is one in which horizontal beams

are supported at each end by substructure

units, called piers. “Under load, the beam's

top surface is pushed down

or compressed while the bottom edge is

stretched or placed under tension.” (Beam

Bridges) The strength of a beam bridge is a

function of its material and the height of its

section (if you were to cut the bridge along

its center, the height of the resulting cross

section). A log can be a beam bridge; as are

those you see over most highway overpasses.

Arch

The arch bridge is an ancient

innovation that has been used for centuries

to create what are arguably some of the

most elegant structures made by man.

An arch bridge is a bridge with a curved span

used to transfer vertical loads to abutments

on either side. The oldest surviving arch

bridge dates to the Greek Bronze Age. Built

using traditional masonry techniques in stone

and brick —materials that are strong in

compression but weak under tension — the

An example of a typical beam bridge. The next time you drive along a highway, note the difference in beam height of the bridges you pass under. Those with extra tall beams are likely designed for trains, while those with shorter beams may be meant for cars or even pedestrians.

Built in the early 14th century, the Pont du Diable in Ceret, France is a beautiful example of a traditional stone arch bridge. This type of construction takes advantage of the compressive strength of stone to achieve spans that would otherwise be impossible.


arch bridge allowed engineers to create long and elegant spans without the use of

modern high tension materials like steel cable.

Cantilever (and cantilever truss)

The cantilever bridge is a type of bridge

that uses two opposing arms balanced along

their centers on piers with the far end of each

arm anchored to an abutment and the end

over the center of the span cantilevering out

into space and connected to the opposing

arm. To reduce the weight of the bridge itself,

large cantilever bridges are made of steel

trusses.

Suspension

The suspension bridge is one of the

most recognizable and iconic bridge types.

Suspension bridges “suspend the roadway by

cables, ropes or chains from two tall towers.

These towers support the majority of the

weight as compression pushes down on the

suspension bridge's deck and then travels up

the cables, ropes or chains to transfer

compression to the towers... The supporting

cables, on the other hand, receive the bridge's

tension forces. These cables run horizontally

between the two far-flung anchorages…

essentially solid rock or massive concrete

blocks in which the bridge is grounded.” (How

Bridges Work)

The design of a bridge over the Firth of Forth was originally proposed by Sir Thomas Bouch. After the tragic failure of his Tay Bridge in 1879, the project was awarded to English engineers Sir John Fowler and Sir Benjamin Baker.

The Roebling suspension bridge between Covington, Kentucky and Cincinnati, Ohio opened to traffic on January 1, 1867. A prototype for the Brooklyn Bridge, its central span of 1057 feet was, at the time, the longest in the world.


Cable-Stayed

Though they look a lot like suspension

bridges, “cable-stayed bridges differ from their

suspension predecessors in that they don't

require anchorages, nor do they need two

towers. Instead, the cables run from the

roadway up to a single tower that alone bears

the weight… Cable-stayed bridges are a

popular choice as they offer all the advantages

of a suspension bridge but at a lesser cost for

spans of 500 to 2,800 feet (152 to 853

meters). They require less steel cable, are

faster to build and incorporate more precast

concrete sections.” (How Bridges Work)

Truss

A truss bridge is a type of

bridge whose main element is a truss

which is a structure of connected

elements that form triangular units. The

truss bridge is essentially an advanced

form of beam bridge that uses a

framework of members to increase the

section height of the beam with a truss distributes stress through the entire structure,

permitting the bridge to support not only its own weight but also that of its designed load. “While arch bridges provide support from beneath and suspension bridges provide

The Union Pacific truss bridge over Garcitas Creek in Inez, Texas is an example of a quintessential truss bridge. Its design leverages trigonometric principles to provide massive load-bearing capability with minimum weight.

The Assut de l’Or Bridge in Valencia, Spain is a beautiful example of a cable-stayed bridge. It was designed by Santiago Calatrava and completed in 2008.


support from above, a truss bridge strengthens the road itself.” (How Does a Truss Bridge Work?)

The Truss Bridge

The earliest known documentation of a truss bridge dates to 1570 and is found in

Andrea Palladio’s Four Books on Architecture. (Hayden) Before the Industrial Revolution,

most bridges were made of stone like the one pictured here, which dates to the 16th

century. Stone bridges are amazing structures. They utilize many of the same geometric

and structural principles that underpin truss and suspension bridges, but they are limited

in span due to the high weight of stone and its relatively poor mechanical properties in

tension.

Even within the category of Truss Bridge, there are many, many sub-categories of

truss bridge designs, including the following:

Allan Baltimore Burr Arch K Long

Bailey Bollman Howe Truss Lenticular Parker

Pratt Vierendeel Pegram Warren Bowstring

Take some time to research a few of these truss designs on-line. Select 3 trusses

from the list above and provide a brief description and a sketch in the space provided on

the following page.


As you can see, truss bridges come in many different designs. The one thing they

have in common is the use of triangles to bring stability to the structure.


The Strongest Polygon

You may have already learned that a triangle is a

stable polygon. Once put together, the shape can't be

changed by pushing or pulling on the sides. Triangles

are unique in that sense. The angle between two

structural members is based on the length of the

opposite member. The angle “a” is fixed based on the

relative length of side “A.” Just like the angle “b” is

fixed based on the relative length of “B” and “c” based

on “C.”

“Triangles are strong because of their inherent structural characteristics. The

corner angles of a triangle cannot change without an accompanying change in the length

of the edge. Therefore, in order to change a triangle’s shape, an edge must collapse.”

(Why are triangles so strong?)

For a quick demonstration of this, consider the diagram below. If each of these

beams was of infinite strength (i.e. they cannot be made to buckle) the only way to

deform each shape would be by changing the angle at each joint. What would happen if

you were to apply a load of infinite force and the vector shown to each of the shapes

below? Draw the deformed shape on your page using a dotted line.


In developing a truss bridge, our goal is to create a rigid structure, but our

structure is composed of joints which provide a certain degree of freedom to the

members of our structure. If you think of our truss shapes as a mechanism — a system or

structure of moving parts intended to perform a function (Collins English Dictionary) —

then our goal for this project is to develop a poor (non-moving) mechanism.

If you think of the shapes above as planar mechanisms with motion possible only

at their joints, you see that their structure is inversely related to their “mobility” at each

joint. (For the purpose of this discussion, mobility is defined as the internal relative

motions of these joints, neglecting the movability (in six degrees of freedom) of the

structure as a whole.) That is, to the extent that each joint can move, these shapes may

serve as a great mechanism (e.g. a four bar linkage), but they would also serve as a poor

structure (e.g. a bridge).

This phenomenon is described handily by the Kutzbach criterion, which shows us

that it is possible to determine the mobility of a mechanism simply by counting the

number of links and the number and types of joints included in that mechanism.

“Consider that before they are connected together, each link of a planar mechanism has

three degrees of freedom when moving relative to the fixed link. Not counting the fixed

link, therefore, an n-link planar mechanism has 3(n - 1) degrees of freedom before any of

the joints are connected. Connecting a joint that has one degree of freedom, such as a

revolute pair, has the effect of providing two constraints between the connected links. If

a two-degree-of-freedom pair is connected, it provides one constraint. When the

constraints for all joints are subtracted from the total freedoms of the unconnected links,

we find the resulting mobility of the connected system.” (Uicker, Pennock and Edward)


𝒎 = 𝟑 𝒏 − 𝟏 − 𝟐𝒋𝟏 − 𝒋𝟐 where:

m = mobility of the system

n = number of links

j1= number of joints with 1 degree of motionj2= number of joints with 2 degrees of motion

Using this criterion, in a mechanism in which m = 0, motion is impossible and the

mechanism remains rigid. If the equation yields m = 1, then constrained motion can be

generated using a single input motion (a good mechanism but a poor structure). If m = 2,

then two input motions are required (a loose mechanism and even poorer structure). If m

= -1, then the mechanism has redundancy. For our purposes, we are seeking rigid

structures —mechanisms in which m = 0.

Consider the graphic below. using the equation on the previous page, calculate

the mobility of each of the following planar mechanisms. (Because we are only

considering structures with pinned joints, all the mechanisms in this example will use j2 =

0.) Which provides the highest mobility? Which provide(s) the greatest rigidity? Which

does so with the fewest possible members?

This project uses 3D printing to explore the strength of triangles in the

development of a 3D printed truss bridge. In the first part of this project, your team will

explore just how stable triangles are by creating three dimensional versions of the

structures above. In the second part of the lesson, your team will create truss bridges

that apply the knowledge you’ve learned.


Identify the Problem

What is the problem you’re trying to solve? This first, critical question forms the

foundation for all the work to follow. The answer to this question is known as the

Problem Statement.

In the professional world, the audience for this statement can be the owners or

manufacturers of a product, a client, or an end-user, among others. It is essential that this

statement be phrased in such a way that it can be understood by each of these very

different stakeholders. To provide this clarity, a problem statement is often conveyed in

the following format:

To design a ___________ for _____________ that _________________.

In this section, you will develop a problem statement in this format, using a

worksheet in the following pages. There are six critical questions that must be answered

with every design project: Who? What? Where? When? Why? And How? As depicted in

the chart below, the Problem Statement answers 4 of them.

The Questions of Design Question Answer

Who?

Who is the intended end user of this device? (This is important for identifying

constraints and criteria for this user’s needs.)

Problem Statement

What?

What is the intended function of the device? What may also be used to describe the device (e.g. a toy car), but don’t let that

description limit you.

Problem Statement

Where? Where is the device intended to be used? (e.g. will it be used on a smooth table? In a

sandbox?) Problem Statement

When? When will the device be used? (e.g. is it something that requires daylight?) Problem Statement

Why? Why is this device being created? (e.g. why is it important that this device exist?) Set the Stage

How? How will you solve the problem? Design Process


Based on the knowledge you gained during the Set the Stage phase, think about

the project and the challenge you’ve been presented. You have been asked to design a

small model of a truss bridge. What is your goal for this model?

_____________________________________________________________

With this as your overarching goal, use the Problem Statement Worksheet below

to determine the inputs for your problem statement. Some answers have been provided

for you. (For this project, you will be creating a model of the device described in the

chart below, rather than the real thing.)

Question Answer

Who? (e.g. a person

traveling on foot)

What? A (model) bridge

Where? (e.g. spanning San Francisco Harbor)

When? (e.g. for the opening

of the America’s Cup)

This model will be designed to span an area in the classroom defined by your instructor.

Why? (e.g. as a means to allow fans to view

the race from above)


Now use the answers from the worksheet on the previous page to frame a

concise problem statement using the format provided below. (Though it will be critical to

the development of your product requirements, the why need not be included in a

problem statement.)

Collaboration is critical to success in engineering as it is in many fields. Once

you have documented your idea for the goal for the project, confer briefly with your

team to discuss. Compare each other’s problem statements and come to a consensus

on a problem statement that you believe your team has the knowledge and resources to

attempt. For example, if your problem statement reads “To design a truss bridge capable

of spanning the English Channel,” your team may not have the requisite knowledge with

which to design or test the bridge. In this scenario, you would be wise to take on a lesser

challenge. In the space below, document the revised problem statement of your group.

Problem Statement (first draft):

To design a ___________ for _____________ that __________________. (What?) (Who?) (What? When?)

Where?)

Problem Statement (group consensus):

To design a ___________ for _____________ that __________________.

(What?) (Who?) (What? When? Where?)


Identify the Criteria & Constraints

Criteria (the plural of criterion) are requirements or characteristics that define

success in a new project or device. Constraints are limitations or restrictions that limit the

possible implementations by which you achieve that success.

In starting any new design project, you might perform a number of studies to

determine the criteria and constraints of your project. For the design of a bridge, these

might begin with a feasibility study comprising: a topographical survey; an environmental

impact assessment (EIA); a social impact assessment (SIA); traffic, hydrological and

geotechnical investigations; and bathymetric surveys as well as financial analyses. The

results of these analyses would provide constraints and criteria for your project, including

the type (movable, fixed) and subtype (truss, cable-stayed, et al.) of your bridge design.

For an historical example of a feasibility study for the construction of a new bridge,

please take a moment to review the 2012 Northgate Pedestrian Bridge Feasibility Study

Report, prepared by the King County Department of Transportation. You can skim

through this original feasibility study by downloading it from the Student Resources tab in

your STEAMtrax dashboard.

Criteria and constraints provide the framework within which you will design a

solution to your problem statement. In any new project, it is important that you define

these before you begin generating solutions. If you begin innovating before defining this

critical framework, you may invent a solution that doesn’t meet the requirements of your

project. The output of this phase of the project is a Product Requirements Document

(PRD) that outlines the requirements for your project based on the criteria for its success

and the constraints that limit that success.

criterion n. a principle or standard by which something may be judged or

decided (source: Oxford English Dictionary)

constraint n. a limitation or restriction (source: Oxford English Dictionary)


Requirements = criteria - constraints

Determining Criteria

Now that you have completed your problem statement, consider how different

aspects of the problem statement (answer column) will affect the criteria for your design.

During this short exercise, you will meet with your group to create a list of the criteria for

your project’s success. By using the answers provided previously (who, what, where, etc.)

as a foundation for this exercise, you will ensure that your criteria align with the problem

statement above. For example, if you are designing this model truss bridge (what) for

use in a classroom (where), you will need to ensure that the model can be readily

mounted to a water source.

Using the space below (or an attached sheet of paper), list the criteria that your

model turbine must meet to be successful. Some answers have been provided.

Answer Criteria

Who?

What?

Where?

A span defined by your teacher (e.g. between two tables of known distance

apart).

When?

Why?


Constraints

What limitations will restrict your solution to the problem? What materials do you

have to work with? What capabilities do you and your team have to help the project

succeed? Take a moment, with your team, to list several of these constraints in the space

provided below or on an attached sheet of paper. A few constraints related to the

content of this project have been provided, below.

Constraints

Discuss & Guide

During this section, you will outline the requirements for your device. It is

important to have a robust list of design requirements, because design requirements

form the structure around which all future design decisions are made. If you add a design

feature that prevents you from meeting one of these requirements, the design may be a

failure. Most complex engineering projects include a list of hundreds of design

requirements and specifications. For this project, we will start with just five.

Meet with your group to determine and document at least five (5) requirements for

your bridge model. Build on your prior work to be sure that these requirements reflect

your knowledge of the criteria and constraints that drive your project. To ensure that you

meet the foundational goals for the project, consider the who, what, where, when and


why that you outlined previously. Be sure that your group can justify, logically, the

incorporation of design requirements based on answers to those questions.

Not all requirements are created equal. Consider a real bridge. It is very important

that it be safe and survive all forces of traffic and elements that are applied to it. The

aesthetic of the bridge, while important, is not as important as safety and longevity. As

you begin to outline your requirements, be sure to weight their relative importance, using

the scale below. Because not every requirement can be critical, you may only use each

number three (2) times in your ranking.

Once you have completed a list of five requirements for the new device, outline

them in the space provided, including a name for the requirement, its ranking, and a brief

description written to read in the following format “the device shall ______________.”

Number Weighting (1, 3, or 5) Title (Description) The device shall….

1

2

3

4

5

1 = least important or “nice to have”

3 = important or “must have to be competitive”

5 = critical or “without this, the device will fail”


Research & Explore

Now that you have explored and created the structure of your design project and

outlined a series of design requirements, it’s time to do some hands-on exploration of

some of the constraints that will challenge

your abilities to execute on those

requirements. Hands-on research and

exploration allows you and your team to

develop a firsthand understanding of

these constraints from which you can

innovate. One of the quickest and most

powerful ways to get firsthand experience

is to develop a prototype.

There are many types of prototype. A number of them are listed in the box at right.

During this phase of the project you and your team will construct and experiment with a

proof of concept (POC) prototype that demonstrates that basic function of your device.

This prototype will utilize many of the same components and principles that will be

included in your final design, but it will provide only basic performance. You will use this

prototype as a learning tool from which to improve your design as you move through the

next phases of the iterative engineering design process.

Images: www.Dyson.com

proof of concept n. evidence, typically deriving from an experiment or

pilot project, which demonstrates that a design project, business proposal, etc. is

feasible. (source: Oxford English Dictionary)

TYPES OF MECHANICAL PROTOTYPE

Visual (or “looks like”)

Proof-of-Concept (or “breadboard”)

Presentation (or “looks like/works like”)

Pre-Production (or “factory sample”)


During this initial prototyping exercise, your

team will develop two sets of components — a set

of flexible struts to reinforce the lessons in

Setting the Stage, and a model truss bridge using

a simple, 3D-printed connector. Using the first

output of this phase — the struts —you and your

team will be able to evaluate how the elements

you explored in Setting the Stage contribute to

the performance of your model. Using the second

component — the truss bridge model — you will

see these principles in action.

Take note of how this version of the device performs and begin thinking about

areas for improvement. Your goal in the later phases of this project is to improve on this

basic design by designing and testing your own truss bridge based on what you learn

from this proof of concept prototype.

Use the step-by-step BlocksCAD instructions found in your STEAMtrax dashboard

under Classroom Guide > 3D Printing Files to create this POC prototype, using

BlocksCAD.


CAD (Computer Aided Design) is the use of computer systems to aid in the

creation, modification, analysis, or optimization of a design. In the engineering

professions, CAD is most often used to design three dimensional (3D) models that are

used for the communication, analysis and manufacture of mechanical parts and

assemblies. There are many

powerful CAD modeling tools

available with which to create

the 3D models. The software

used for this module is

BlocksCAD. BlocksCAD is a simple-to-use, cloud-based 3D modeling tool that

incorporates “complex programming and mathematical functions.” Unlike traditional

CAD modeling tools that rely on graphically modeling new shapes in 3D, BlocksCAD

uses a modeling technique based on computer programming to transform your code into

three dimensional objects. This means that, during the course of this project, you will not

only learn about 3D modeling, you will be introduced to the rudiments of computer

programming.

Refer to BlocksCAD instructions found in your STEAMtrax

dashboard under Classroom Guide > 3D Printing Files to create

this POC prototype, using BlocksCAD.

Things to do and notice

Activity 1 > The first activity is open-ended and intended to explore the stability of

triangular structure. Experiment with this structure using 3, 4 and 5 members. See

how you can stabilize the shape by adding members. Try to predict how these

shapes will behave. (This is a good time to use your trigonometry skills to

calculate the forces on each strut. A hint to get you started: all the struts are the

same length, making the shapes equilateral triangles.)

Activity 2 > Working with the bridge model, you and your team will put some

weight on the roadway and see how well your bridge holds up. If you increase the

load enough, the bridge will break. Can you anticipate where the break will likely

occur?


Set the bridge up between two books or similarly rectilinear support such that it

spans a measured distance. Apply weight slowly until the bridge collapses.

Document how much weight your bridge held just before it collapsed in the space

provided below. Collect the same data from other groups and document the

average performance of this POC design, in the space provided. (If dowels

break off in your connector pieces, you can pry out the broken struts with a dental

pick and replace them.)

GROUP 1 2 3 4 5 6

Span (cm) AVERAGE

(SUM / 6)

WEI

GH

T A

T FA

ILU

RE

(kg)

Proof of Concept (POC) Model


Develop a Solution

Idea Generation

During this task, you will be generating ideas to improve upon the proof-of-

concept prototype you generated in the previous phase and incorporating

requirements you identified earlier. For this lesson, you’ll be learning an interesting idea

generation technique — the SCAMPER method.

SCAMPER

SCAMPER is “a creative thinking technique that helps students imagine the world

in a completely new way.” (Eberle) Initially coined by creative thinking pioneer Alex

Osborne, this methodology was “fleshed out” by educator Bob Eberle, in his 1971 book

Scamper: Creative Games and Activities for Imagination Development. (SCAMPER - The

Key to Innovation and Entrepreneurial Success!) This tool “helps you generate ideas for

new products and services by encouraging you to think about how you could improve

existing ones.” (SCAMPER) SCAMPER is a mnemonic to help you remember the process

involved in this method. It stands for: Substitute, Combine, Adapt, Modify, Put to another

use, Eliminate, Reverse.

A delicious example of the SCAMPER method. (Image Source: Creative Universe)


During this phase, you will use SCAMPER to improve upon your proof of

concept by substituting, combining, adapting, modify, putting to another use,

eliminating, or reversing element of its design. Your goal is to improve on your earlier

design by creating a truss bridge model that will support more weight than the proof of

concept prototype. Some of the elements below will be more applicable to this project

than others.

(S) Substitute Remove some part of the accepted situation, thing, or concept and

replace it with something else. Look at the elements of your POC and ask: Can

any components of this be replaced? Can I change their shape? Can I use other

materials? Can the rules be changed?

(C) Combine Join two or more elements of your device and consider ways that

such a combination might move you toward a solution. Ask: What components

could be combined? Can I merge this device with something else? Can I include

different materials or components?

(A) Adapt Change some high level attribute of your device. Ask: What else is this

like? What could it emulate? What can I incorporate from other industries or

applications? (e.g. biomimicry)

(M) Modify Consider multiple aspects of the device, including: size, shape, other

dimensions, texture, color, attitude, position, history, and so on. What can be

modified to improve function? Ask: Can elements be made larger or smaller? Can

other elements or strategies be added to or eliminated from the design?

(P) Put to other use Modify the intention of the subject. Think about why it exists,

what it is used for, what it's supposed to do. Challenge all of these assumptions

and suggest new and unusual purposes. Ask: Why does this exist? Could this

device or its technology be applied to a new need?

(E) Eliminate Remove components, simplify, reduce to core functionality. Ask:

How can this be simplified? What features can be minimized or eliminated without

ruining the function of the device? Does this elimination improve function?

(R) Reverse/Rearrange Change the direction or orientation. Turn it upside-down,

inside-out, or make it go backwards. Ask: If the device were assembled in a

different way, would it be better, worse, or changed entirely?


Meet with your team to SCAMPER around the current implementation of your

project (the POC) to improve its performance. Document your output using a web

diagram formatted like the one shown here. It is recommended that you use large format

paper or a whiteboard for this process and copy your work to this page or a similarly

formatted copy.


Concept Sketching

The output of any ideation session is ideas. These can be documented in a

number of ways. The output of

some brainstorms are simply

lists. Others include photos,

magazine clippings, objects or

sketches. By far the most

popular and effective output of

a brainstorm is a concept

sketch. An example of a

professional concept sketch is

pictured here.

For this project, you will be documenting your concepts using a concept sketch

and a brief description of your design.

Step 1 > Divide and conquer. Divide your concepts such that each team member

has an equal number of concepts. Each team member will sketch at least one

concept in their notebook, using the page that follows.

Step 2 > Describe your design. You will document each concept on a single

sheet of paper, including a brief description and a rough concept sketch. To

begin, describe your concept in a sentence or two.

Step 3 > Create a sketch. Add a rough concept sketch to your page. (Attach

additional sheets, as needed.) Show the design from multiple views and be sure to

highlight specific features of the sketch using callouts, as needed. Each page

should follow the format outlined on the page that follows, including: Concept

number, Concept name, features list, and sketch.

Step 4 > Sign it! Be sure to sign and date your concept in the spaces provided.

Inventors mark their ideas in this way — using dates and signatures — to prove that they

were the first to invent a new idea.


Date: _____ Signature: ___________________________

sketch area

Concept #: _____ Concept Name: ___________________________

Description:


Debate & Decide

This is one of the most critical steps in any design project. During this task, your

team will select a single design for advancement to the prototyping stage of the project

using a powerful decision-making tool — the criteria-based matrix.

Employing a rigorous decision-making methodology is extremely important to

effective design, because a great solution to the wrong problem is an even more costly

failure than a poor solution to the right one. It’s up to your team to make sure you’re

solving the right problem. This step ensures that the concept with the best chance of

meeting the goals of the project gets the benefit of this powerful design process.

Begin the process by laying out your concept sketches on a flat surface. Take a

moment to list the pros and cons of each concept on a separate sheet.

Once this step is complete, it’s time to formalize your evaluation and select a

direction for advancement. Because the process of selecting a single concept from so

many good ideas can be difficult, is it often necessary to provide a formal structure for

evaluation. To make this problem simpler, this module utilizes a tool called a Criteria-

Based (or Pugh) Matrix. This matrix is a powerful decision making tool that can be used to

make high level decisions even early in the design process, when very little data is

available on which to make decisions. On a complex project, matrices like these will

often include dozens of concepts and potentially hundreds of requirements on which

each concept is will be judged.

As you determined earlier, in the Discuss & Guide phase of the project, not every

requirement is of equal importance. The Pugh matrix is where the requirement weights

you provided earlier finally come into play. By calculating the estimated performance of

each concept against a requirement and then against the relative importance of the

requirement, you can get a sense of the overall potential of the concept.

criteria-based matrix n. a scoring matrix used for concept selection in

which options are assigned scores relative to criteria. The selection is made based

on the consolidated scores. Before starting a detailed design, there are many

options – this tool helps with selecting the best option. (source: iSixSigma)


To use the Pugh Matrix on the following page, please meet with your group and follow

the steps outlined below. Complete the steps below for each of your concepts,

including the POC prototype. This data will be used in the testing phase to follow. (Attach

a separate sheet of paper, as needed, to document your results.)

Step 1 > Input your concepts. Match the concept number with the space provided

in the matrix. In the description box, jot down a brief description of each concept.

Step 2 > Input your requirement weights. Copy the requirement weights you

provided earlier (in the Discuss & Guide phase) into the corresponding boxes.

Step 3 > Rank your concepts. Take some time to go through your concepts one-

by-one and estimate their performance against each of the five requirements on a

scale of 1 – 4. (For example, if one of your requirement is for child safety, then a

design with a number of small choke hazards might receive a 1. A design with

fewer small parts might receive a 2 or 3. A design with no small parts might

receive a 4.)

Step 4 > Calculate the weighted performance of your concepts. To calculate the

weighted performance of each concept, multiply the score in each box by the

weighting of the corresponding column and add up each of these new scores.

If score = S and Weighting = W, then your total weighted performance (TWP)

can be calculated using the formula below.

TWP = (S1 • W1) + (S2 • W2) + (S3 • W3) + (S4 • W4) + (S5 • W5).

Once you have completed your concept ranking, you will have all the information

needed to select a few concepts for advancement into the next phase — prototyping. For

this project, you will select several top-performing concepts to prototype in the next

phase, using the skills you’ve learned in BlocksCAD. Many innovators advance one or

more concepts into the prototyping phase to test multiple design paths, in parallel. This

provides an opportunity to use the testing phase to experiment with multiple potential

designs.


Total Weighted

Performance

Total

Req

uire

men

ts

5

4

3

2

1

W

eigh

ting

Des

crip

tion

The

proo

f of c

once

pt

prot

otyp

e yo

u de

velo

ped

earl

ier.

Con

cept

PO

C

1 2 3 4

5

6


Model & Prototype

Once you have completed the evaluation of your concepts, as single concept

should emerge as a clear winner. To advance this concept into a prototype, you will

divide the design into its sub-components and model these components for 3D printing.

Your model will be based on the learnings you gained during the development of your

Proof-of-Concept prototype and may share many of the same components.

Meet with your group to divide up the 3D modeling tasks and begin to model

these components using BlocksCAD. Be sure to meet frequently with your team

members to check dimensions and ensure that all the components will fit nicely into your

assembly.

Justify

Once you have a three dimensional model of your design created in BlocksCAD,

be prepared to justify your design in an informal presentation to your classmates that

outlines the benefits of your new design. Your presentation should last no more than five

minutes. Use your CAD model as a visual aid to support your assertions.

During your presentation, take your classmates through the process you used

being sure to cite the requirements around which your design is based and the solutions

you’ve developed to solve for those requirements. Be prepared to incorporate creative

feedback from your teacher and classmates during a brief question and answer period to

follow your presentation. Document that feedback in the space provided below. (Attach

additional sheets, as needed.)

3D Print (1/2)

With your models finalized, upload your .STL files to your local 3D printer and print

a copy of each new rotor design. Assemble your new design.

Feedback:

_______________________________________________________

_______________________________________________________

_______________________________________________________


Test the Design

Now that you have a 3D printed versions of your new bridge model, it’s time to

test it. In assessing the performance of any new device, it is important to benchmark it

against a known standard. In this case, we will use your evaluation of the POC prototype

to determine how successful your group was in improving over that design. The testing

methodology in this module is called “destructive testing.” Destructive testing tests a

material or design until failure. Destructive tests are easier to carry out than non-

destructive tests and infinitely more exciting.

Test Setup

You have already tested and documented the performance of the POC bridge

earlier in this lesson. During this task, you will test the performance of your new design

using the same methods.

Step 1 > Copy the data from your earlier (POC) tests into the chart on the following

page.

Step 2 > Assemble your bridge model over the span identified by your teacher.

For consistency, this should be the

same span as that of the earlier POC

tests.

Step 3 > Begin to apply weights to the center of your bridge model. Apply weight

in small increments until failure occurs.

Step 4 > Document the point of failure. This is the amount of weight that your

bridge could hold directly preceding the point at which it failed.

Step 5 > Document the points of failure for the other bridges in your class.

Step 6 > Average the performance of the new designs and compare to that of the

POC.


GROUP 1 2 3 4 5 6

Span (cm) AVERAGE

(SUM / 6)

WEI

GH

T A

T FA

ILU

RE

(kg

) POC

NEW DESIGN

Analyze & Communicate

In a brief summary report, please describe the performance of your new design

against that of the POC prototype using the data you’ve collected. Also, compare your

design to that of the other groups in your class. What methods did you employ that they

did not (and vice versa)? What methods were the most successful? Why? Please prepare

your summary using the format on the following page.


Summary (One paragraph summary of your process and findings to date, including a description of the development of your prototypes)

.

Test Setup (One paragraph description and a sketch of your bridge as well as a vector diagram of the forces applied to your model)

Test Results (Provide the results of your tests and those of the other groups in the chart below.)

GROUP 1 2 3 4 5 6

Span (cm) AVERAGE

(SUM / 6)

WE

IGH

T A

T

FAIL

UR

E

(kg

)

POC

NEW DESIGN

Conclusions & Next Steps (One paragraph providing a conclusion regarding your findings and outlining next steps)

Project Name: Truss Bridge

Team Members: ___________________________________________

Teacher’s Name: _____________________

Date: _________

Performance Testing Report


Self & Group Evaluation

Please complete the evaluation rubric below and reflect briefly on your

experience with this project so far. Detach this sheet by cutting along the dotted line

below and submit it to your instructor. (Use additional sheets, as needed.)

Project Name Date:

Student Name

Team Members’ Names

Attribute 1 2 3 4 Score

I understand the core concepts of this module

I understand and am effectively applying the design process

I am contributing equally to the success of my group project

My group is working well together

I understand what I will do next

Total

Reflection (Reflect on and describe what you’ve learned so far. Describe what improvements you could make to

enhance your personal and group performance in the weeks to come.)

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Self & Group Evaluation (Preliminary)


Improve the Design

Redesign & Model

Most projects require several small modifications following every round of

prototyping. During this phase, your team will be implementing small tweaks to improve

the performance of your bridge. Consider what you learned from the performance of

your bridge compared to the POC. Consider its performance against that of the other

groups. Where did your bridge fail? At what load? What elements could you substitute,

combine, adapt, modify, put to another use, eliminate, or reverse to improve its

performance?

The CAD modifications required at this point should be minimal. Assign one or

more team member(s) per component to implement modifications to CAD geometry, as

needed, using BlocksCAD. Be sure to save the new file under a different name with a

suffix indicating its revision number. For example, if the original part was named (R0)

truss_bridge (CONNECTOR).stl, your new part might be named (R1) truss_bridge

(CONNECTOR).stl.

Original File Name Revision 1 (R1) Revision n (Rn)

(R0) truss_bridge (CONNECTOR).stl

(R1) truss_bridge (CONNECTOR).stl

(Rn) truss_bridge (CONNECTOR).stl

Getting into the habit of naming files using an easy-to-understand system for

tracking revisions is critical to every innovator working with computer files — particularly

in a collaborative environment. The format above allows files to be easily grouped with

respect to their revision (rev) number when viewing a folder.

Defend

As you did before — during the Justify phase — you must defend your new design

direction before implementing a new 3D-printed prototype. This phase is particularly

important, because it is the culmination of all your past findings and the final prototype

output of this project. You will present the modifications you’ve made to your design in


an informal presentation to your classmates that outlines the benefits of these

modifications.

Present your case in a short (no more than five minute) verbal presentation using

visualizations of your CAD model and the results of your testing to support your new

direction.

3D Print (2/2)

With your model finalized, upload your .STL files to your local 3D printer and print

the revised components that make up your assembly.

Final Bridge Competition

This module is unique in that includes a final, explosive finish. During this task,

you and your classmates will once more test your bridge designs head-to-head to the

point of failure. Perform this test as you did previously and document your results below.

GROUP 1 2 3 4 5 6

Span (cm) AVERAGE

(SUM / 6)

WEI

GH

T A

T FA

ILU

RE

(kg

) POC

DESIGN 1

DESIGN 2

Write & Wrap-Up

Complete the documentation of your project by filling in any missing items in your

Innovator’s Notebook. Use the following page to reflect on the project and summarize

your experience.


Project Name: Truss Bridge

Your Name: ____________________

Teacher’s Name: _____________________

Summary (Briefly summarize the problem you solved, including a description of your group’s solution)

.

Process (Briefly describe the process you followed to solve the problem)

Data (Copy your test data in the space below.)

GROUP 1 2 3 4 5 6

Span (cm) AVERAGE

(SUM / 6)

WE

IGH

T A

T

FAIL

UR

E (k

g) POC

DESIGN 1

DESIGN 2

Conclusions (Describe what you learned during the course of the project and how you applied those learnings to solve the problem.)

Date: _________

Project Final Reflection & Report


Evaluation

Please complete the evaluation rubric and below and reflect briefly on your

experience over the course of this project. Detach this sheet by cutting along the dotted

line below and submit it to your instructor for further evaluation. (Use additional sheets,

as needed.)

Project Name Date:

Student Name

Team Members’ Names

Attribute 1 2 3 4 Score

I understand the core concepts of this module

I understand and effectively applied the design process

I contributed equally to the success of my group project

My group worked well together

Our concept was successful

Total

Reflection:

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Self & Group Evaluation (Final)


Bibliography

Beam Bridges. n.d. 30 12 2016. <http://www.design-technology.org/beambridges.htm>.

Crowell, Mark. Intellectual Property Management in Health and Agricultural Innovation: A

Handbook of Best Practices. Oxford: MIHR, 2007.

Eberle, Bob. Scamper: creative games and activities for imagination development. Waco:

Prufrock Press, 2008.

Hayden, Martin. Book of Bridges. New York: Galahad Books, 1976.

How Bridges Work. n.d. 30 12 2016.

<http://science.howstuffworks.com/engineering/civil/bridge6.htm>.

How Does a Truss Bridge Work? n.d. 30 12 2016.

<https://www.reference.com/science/truss-bridge-work-904e746c81e1146a>.

SCAMPER. n.d. 30 12 2016. <https://www.mindtools.com/pages/article/newCT_02.htm>.

SCAMPER - The Key to Innovation and Entrepreneurial Success! 11 2016. 30 12 2016.

<https://steemit.com/innovation/@steemint/scamper-the-key-to-innovation-and-

entrepreneurial-success>.

Why are triangles so strong? n.d. 30 12 2016. <https://www.reference.com/math/triangles-

strong-7ae25bf47214a972>.

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