intro bridge project

7/29/2019 Intro Bridge Project

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Problem Definition: Design a Bridge to span agiven distance while supporting a maximum

load using a minimum materials.

Bridge Project


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Project Goals

The goals for this project are for students to: Learn the design process.

See practical applications fortrigonometry, physics,

and engineering statics (force analysis).

Improve skills associated with collecting data anddrawing meaningful conclusions.

Experience the usefulness ofprototype testing.

Recognize the necessity ofgood communication

skills for engineers by completing memos, reports,drawings, and presentations.


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Introduction to Bridge

Bridge Type

Truss BridgeArch bridge

Suspension BridgeCantilever Bridge


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Truss Bridge

Truss design is

to support the

bridge deck

The truss may

have ompression

or tension The joint of truss

is important
http://upload.wikimedia.org/wikipedia/commons/c/c5/RRTrussBridgeSideView.jpg


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Truss(force analysis) Loads members in tension and compression.

Members are pinned atjoints (Moment = 0).

Triangles provide stability and strength.

Top members in Compression.

Bottom members in Tension.

Hint - Imagine entire truss wrapped in rubber skin, so you

have a large rubber box. When you bend it, where would the

wrinkles be? They indicate compression.


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Beam

Ways to strengthen members in bending.Decrease overall length (deflections).

Cross section design (moment of inertia)

Use stronger materials (elastic modulus).

Tension

Compression

Steel

=

Axis of

bending

vs.


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Arch bridge

Appear mostly

in Ancient time

New arch

bridge is

modified to

reduce thematerial


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Function of Arch structure

Puts members in compression.

Need horizontal support at abutments.

Abutment


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Suspension Bridge

Replace the

Beam with

cable

Reduce the

need for the

Pier , Girder

and Truss


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Suspension

Puts members in tension.

Carries weight up to the top of the towers.

Good for long spans.


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Cantilever Bridge

No support at

the bridge it

self

The material

must be very

strong Or the structure

must be

different


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Box Girder Bridge

Box structure reduce

the weight and

material

Increase the strengthon top and bottom to

resist compression

and tension


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Project Constraints

Size: See above & 100 stick limit per bridge

Shape: Original ideas encouraged!

Strength: Must support a minimum of 15 lbs.


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Constraints:

BuildingMaterials

100 Wood tongue depressors (6) Glue guns and glue sticks and

wood glue

String


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Scoring Equation

Score = Load at Failure(performance)

Weight of Bridge(cost)

As engineers, you want to maximize the

load held using the least amount of material.


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Testing Procedure

2 dowel

2 x 6

thin plate

testing jig


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Project Break-down

Project Intro (Problem Definition) Component Strength Tests (Information Gathering)

Individual Brainstorming of Ideas (Idea Generation)

Group Prototype Brainstorming (Idea generation)

Prototype Selection (Idea selection)

Full-Scale Prototype Construction (Implementation)

Prototype Testing (Information Gathering)

Engineering Analysis w/ software (Information Gathering) Redesign (Idea generation)

Final bridge construction (Implementation)

Final Test Competition! (Information Gathering)


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Project Schedule

Timeline:

Prototype Design, Build, Test 1 week

Final Design, Build, Test 2 weeks

Presentation and report 1 to 2 classes

after Final Test


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Grading

Design and testing

Bridge Ideas -10%

Components test Memo-5%

Prototype bridge performance-5%

Draft Report-5%

Project reportBridge Final Presentation-10%

Competition-5%


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Engineering Fundamentals

Mechanics of Materials

Construction Methods & Hints!


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What is the easiest way to

break a tongue depressor? Pull?

Push?

Twist?

Shear?

Bend?

Engineering terms - tension, compression, torsion,shear, & bending

Principle of Scissors


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Bending! Thus bridge design Dos & Donts:

DONTs avoid bending bridge members when

possible.

avoid compressing long bridge members -causes buckling (a kind of bending).

DOs

load members in tension and compression

(short) when possible.

brace bending members when possible.


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Bridge Type we have learned

Truss Bridge

Arch Bridge

Suspension Bridge

Cantilever Bridge

Box Girder Bridge


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Quiz

Which orientation of a beam is stronger

under bending and why?

Arch members are in T or C?

Label members in T and C

I

Ivs.Axis of

bending

C C

T T T


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How can you improve your

bridge design? Incorporate truss structure (triangles).

Design a 3-D structure from the start!

Use short members in compression. Use string for tension members.(Reduce material and

weight)

Avoid overloading joints.

Strengthen base supports and load point.


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Component Test-Compression

and buckle Test-1 Compress your spaghetti until it start to buckle(When you dont feel

you need to apply additional force but the structure still keep bending)

Hold(use you hand) the center point to see how much force you need

to increase to have buckling

Hold another two point to see how much force you need to increase to

reach buckling


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Component Test-Compression

and buckle Test-2 Cut the spaghetti in half and try again

Cut the spaghetti in half again and try again

Record all the force and TestSituation


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Tension Test on the joint

Specimen preparation

Use four depressor

Two as a group. Glue them together Drill one hole on the each group

Overlap two group according to

test procedure and glue them together

Use hook to hold the structure

Start tension and compression test by

force gauge and scale

Do unit conversion if necessary

Take your record home and make excel plot

and report


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Fatigue Test

Bend Paper clip and count how many cycle

it is needed to break it!

Test 5 Paper clip


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Torsion Test

Twist a chalk and see how it break

Explain why it happen(explain in

Components test Memo )

intro bridge project

Documents