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Term Project: Balsa Wood Bridge Part 1

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## Term Project: Balsa Wood Bridge Part 1

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**Turning Ideas Into Reality**Engineering Design Process Read section 2.2, pp. 37-47**What is the difference between an optimist, a pessimist and**an engineer? Optimist: the glass is half full Pessimist: the glass is half empty Engineer: the glass has a 50% overall inefficiency**Engineering Job Functions**• Analysis • Design • Test • Development • Sales • Research • Management • Consulting • Teaching In your project you will • “Research” • Design • Analyze • Build • Test • And learn about the engineering design process**you want to build a bridge**The Engineering Design Process Span > 30cmMass < 30g made of Balsa etc. Rules • browse web resources • look at Seattle bridges • study rules etc. 1. Customer Needor Opportunity 2. Problem Definition/ Specifications 3. Data and Information Collection 4. Development of Alternative Designs 5. Evaluation of Designs/ Selection of Optimal Design 6. Implementation of Optimal Design Deliverable 1 Analyze Designs (software) Deliverable 2 Build and Test Deliverable 3 Note: this last one is not quite true!**Cautionary Notes:**1. Technically our last step (Testing) would NOT be the implementation. • It would still be part of step 5, finding the optimal design. • We would test and then evaluate the results to optimize. 2. There are different versions of the Engineering Design Process. The one presented here is just one of them.**Example: What went Wrong?**The Tacoma Narrows Bridge Disaster**Example: Engineering Design in Action**Mars Rover Curiosity in class: 0:00-0:50 and 9:45-16:00 at home: watch the rest (pretty amazing)**What is left today?**• rules • some physics without math • deliverables • links • forming teams • materials and logistics Note: the second part of the presentation will cover the software and questions.**Let’s Start the Modeling Software …**You can find the software on the project tab of our website: http://seattlecentral.edu/faculty/rheller/Engr110/classproject.html and clicking on Modeling Software Or you can go directly to: http://www.jhu.edu/~virtlab/bridge/truss.htm**How to find the Modeling Software**Click on Class Project**How to find the Modeling Software**Click on Modeling Software**How to find the Modeling Software**Read the instructions Then … To start click on bridge truss**Bridge Terminology**• Your bridge will have • Two trusses • Joints or Nodes • Members • One fixed node • One horizontal rolling node • Loads (at least one)**What does the software do?**For a given LOAD the software will calculate the FORCE(compressive or tensile) in each member. The software can only do this if you follow the RULES**Bridge Rules**• Your bridge MUST have • One fixed node • One horizontal rolling node • Loads (at least one) • And (most importantly) … N= # of nodes (including the support nodes) M= # of members**How many members?**M = 7 How many nodes? N = 5 M + 3 = 2 N 7 + 3 = 2 x 5**Why?**• To find out take STATICS, Engr214 (offered in fall) • Statically determinate system**Modeling a Bridge**Step 1: Start with NODES**Modeling a Bridge**Step 2: Convert one node to fixed node and one to horizontal, rolling node**Note on fixed and rolling nodes**• You have to first create a node. • Then you select ‘fixed node’ and click on the node you want to be fixed. • You cannot click on fixed node directly.**Modeling a Bridge**Step 3: Add members**Modeling a Bridge**How many members? How many nodes? M + 3 = 2 N 14 + 3 = 2 x 9 17 = 18 (oops)**Modeling a Bridge**Add a load … … or better two Error Message**Modeling a Bridge – Correct version**How many members? How many nodes? M + 3 = 2 N 15 + 3 = 2 x 9 18 = 18**Modeling a Bridge – Correct version**Click on Calculate Then click anywhere on the grid …**What does this mean?**Find the total load: Find the member under the highest compression: Find the member under the highest tension:**What are you looking for?**• Note: the loads are relative. Doubling the load will double all forces. • For a given load, you want the maximum compressive and tensile forces to be as small as possible. • If the material behaves better under tension, then your tensile forces can be a little higher.**Let’s Form Teams**• Find a team member. • Make sure you have matching schedules. • Exchange email and phone info. • When you have a partner, come to me and I will write down your names. Have fun!