Slide1: Problem Definition: Design a structure to span a given distance while supporting a maximum load using a minimum of materials. Bridge Project


Project Goals: Project Goals The goals for this project are for students to: Learn the design process. See practical applications for trigonometry, physics, and engineering statics (force analysis). Improve skills associated with collecting data and drawing meaningful conclusions. Experience the usefulness of prototype testing. Recognize the necessity of good communication skills for engineers by completing memos, reports, drawings, and presentations.


Project Break-down: Project Break-down Project Intro Individual Brainstorming of Ideas Component Strength Tests Group Prototype Brainstorming Prototype Selection Full-Scale Prototype Construction Prototype Testing Engineering Analysis w/ software Redesign Final bridge construction Final Test Competition! DESIGN PROCESS Problem Definition Idea Generation Information Gathering Idea Selection Implementation


Project Constraints: Project Constraints Size: See above & 100 stick limit per bridge Shape: The bridge must have a clearly identifiable, realistic “deck” or passage from one end to another, to simulate the road surface. Any shape that fulfills the constraints will be allowed. Strength: Must support a minimum of 15 lbs.


Testing Procedure: Testing Procedure 2” dowel 2” x 6” thin plate testing jig


Slide6: Your bridge must have a easily identifiable road deck. The elevation difference of the road deck has to be less than 4 inches. The metal plate will be used to simulate a car running on the road deck, thus its length will be parallel to the bridge.


Building Materials: Building Materials Wood tongue depressors (6”) Glue guns and glue sticks String


Project Schedule: Project Schedule Timeline: Prototype Testing – 2 weeks Final bridge Testing – 1 week Presentation and report – 1 to 2 classes after final test


Grading: Grading 15% Group Final Bridge Report 5% Group Oral Presentation 20% Bridge Project + HW assignments (bridge ideas, component test memo, bridge analysis assignment, performance of the bridge, etc..) + Review handout for additional information.


Performance Scoring Equation: Performance Scoring Equation Load at Failure(lbs) Score= --------------------------- Weight of Bridge (lbs) As engineers, you want to maximize the load held using the least amount of material.


Engineering Fundamentals: Engineering Fundamentals Mechanics of Materials Bridge Examples Construction Methods & Hints!


What is the easiest way to break a tongue depressor?: What is the easiest way to break a tongue depressor? Pull? Push? Twist? Shear? Bend? Engineering terms - tension, compression, torsion, shear, & bending


Bending! Thus bridge design Do’s & Don’ts:: Bending! Thus bridge design Do’s & Don’ts: DON’Ts avoid bending bridge members when possible. avoid compressing long bridge members - causes buckling (a kind of bending). DO’s load members in tension and compression (short) when possible. brace bending members when possible.


Next, Let’s examine some existing bridge designs : Next, Let’s examine some existing bridge designs Beam Arch Suspension Truss Pre-Stressed Box Girder


Beam: Beam Ways to strengthen members in bending. Cross section design (moment of inertia) Use stronger materials (elastic modulus). Decrease overall length (deflections). Use reinforcement. Tension Compression Steel = Axis of bending vs.


Cross section make a difference(1): Cross section make a difference(1) A “Wide” cross section movie A “Tall” cross section movie


Cross section make a difference(2): Cross section make a difference(2) A “Wide” cross section (1.54) A “Tall” cross section (1.507)


Arch: Arch Puts members in compression. Need horizontal support at abutments. Abutment


Suspension: Suspension Puts members in tension. Carries weight up to the top of the towers. Good for long spans.


Truss: Truss Loads members in tension and compression. Members pinned at a joints(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.


Pre-Stressed Box Girder: Pre-Stressed Box Girder Pre-fabricated off site. Steel wires (in tension) run through base of box sections. Why? Steel wires Pier Road deck


Quiz: Quiz Arch members are in T or C? Which orientation of a beam is stronger under bending and why? C C T T T Label members in T and C (by inspection)? I I vs. Axis of bending


How can you improve your bridge design?: 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. Avoid overloading joints. Strengthen base supports and load point. Maximize moment of inertia of cross-section.


Today’s work – Component test: Today’s work – Component test Purpose: to find out the strength and characteristics of the bridge building materials. What to do: 8 tests to be done by the whole class. 2 tension test, 2 compression test, 4 bending/torsion test. Each group will be assigned one test.