Unit 5- Structures

In case of my absence you will be working on a bridge building unit. The ultimate goal will be for you to construct a bridge out of balsa wood and wood glue. This is a three part project.

This is an individual component and should last about three days. (20 points individual)

1. On the science computers in my room is a program called the "West Point Bridge Builder." Start the simulation, on page three you are given the option to have a starting height for your bridge. Set the starting height to 16 meters. Failure to change the start height will result in a bridge that won't fit the gap. Ensure that you do not use a central structural support or anchors since your bridge you build will not have them. Your ultimate goal is to build the most stable and cheapest bridge. Be sure to use the computer that is assigned to you.
2. To test your bridge, click the "Test" drop down tab, then click on "Load Test" to see if your bridge can stand. After the test is complete, click on the "drawing board" button under the test drop down to examine which Trusses were weakest.
3. The cost of the bridge is given in the simulation and the strength of the bridge will be given on a table on the simulation.
   1. 1 point will be taken off for every $50,000 you are over your budget of $550,000 for your bridge.
4. Secondly, I will be looking at your tables for your compression (RED) values on the side of your table. Compression is where a bridge truss (the supports of a bridge) are being compressed under the weight of the bridge/load. Any value that is above 0.3:1 for a weight/force ratio loses stability. Any value that is below a ratio of 0.5:1 is considerably unstable, and any values that are 1:1 or greater will collapse. You will lose 0.5 points for each truss that has a ratio that is greater than 0.3:1 and 1 full point for each truss that is greater than 0.5:1
5. Third- I will be looking at your tension (BLUE) values on the side of your table. Tension is where the trusses are being pulled apart, too much tension and they can be ripped apart. I will be allowing you four free trusses that exceed the safe ratio limits without penalty.
6. Sometimes a truss may be highlighted purple, this is a slenderness issue that means your truss is to long and skinny. Try to adjust the dimensions of your bar, making it thicker, solid, or a different type of steel.
7. The balance between compression and tension are what makes bridges stable. Your job is to make your bridge as stable as possible.
8. If I am gone, save your best bridge to the desktop of your computer and I will grade it when I return.
   1. To save click the "save as" button
   2. Save to the desktop
   3. Call the file your name and the hour you are in.
   4. If you do not save it properly, it will be erased and you will need to redo it.
   5. You can take a screen shot and email it to both me and yourself. If you do this, have the sub record the price of your bridge and the number of truss ratios that are red or blue.

Part Two - (15 Group Points) - Scaling and Modeling the Bridge

Your group needs to decide ultimately who has the best designed bridge based on strength and costs. You will then need to convert the length of each beam on the simulation to a new length used for the actual bridge you will be building. Create a table, either on google sheets or on a piece of notebook paper and do the conversions for each truss.

1. To do this calculation you will need to find the scaling for your bridge. In the simulation, with a height of 16 meters, you will find the gap length is 36 meters wide. (The separation between each side of the bridge is 36 meters long.) The separation on my tester is 46.5 cm long with a 5 centimeter platform on both sides. The total length of my platform is 56.5 cm.
   1. You need to find a scaling for how to scale each of your trusses so that it will fit on the tester.
   2. If you scale each beam to small the bridge will not fit the gap.
   3. If you scale each beam to large, it may be to big to fit properly on the machine and thus will break.
      1. I would recommend using google sheets. Once you know the appropriate conversion, you can have Google sheets do all the conversions for you. Simply share your sheet with me to receive credit.
2. Once your group has everything scaled, make a full sized blueprint for your bridge. You will be cutting trusses to be the same length as your blueprint to help you map out where each piece goes.
3. On the blueprint label each truss so that it matches up with your table and with your simulation
4. Color code your blueprint to show where you anticipate having a lot of compression or tension.
5. You will be constructing your bridge out of Balsa wood. Each stick of Balsa wood is 36 inches long. Your group will need to calculate exactly how much Balsa Wood you will need to fully construct your bridge. You want to keep the costs as low as possible, while at the same time trying to ensure that you will have enough materials to complete the tasks.
   1. You will need to construct your bridge twice, essentially once for the left and right side of your bridge. You will also need to account for supports running between your bridge. A separate of about 3 inches is an appropriate gap for your bridge. These trusses are more or less to hold your bridge together, but if you have too few it can cause your bridge to bend and break. If you have too many they add unnecessary weight.
   2. You will need to tell me how many sticks of Balsa Wood you will need to complete your bridge. If you don't have enough materials and need additional sticks your group will be penalized 2 points.

Part Three - (10 points) -

1. Your group will be constructing a bridge to test in my bridge tester. Your group will get a 5/10 if your bridge meets the criteria of the gap and can fit the tester.
   1. Stronger bridges will get a 10/10
   2. Weaker bridges will get between a 5-9/10, depending on how other bridges perform.
   3. Bonus points will be given to the strongest bridges across all four sections of PoE.
      1. First Place +5
      2. Second Place +3
      3. Third Place +2

Part Four - Group Video Reflections (18 points)

Your group will need to make a 2-5 minute video walking us through your bridge. You will need the following recordings! Everyone must contribute- Your group will need to create a YouTube video that will be shown to the class. You may use the “Windows Movie Maker” app on the school computer, chose to use i-video, or any other video creating device. Your video must include:

1. (5 points) = You will provide an in-depth walk through of your bridge. This needs to include materials and costs as well as where you think your bridge is the weakest and why. Walk us through both your bridge and the blueprint.
   1. Show your bridge
   2. Show your schematic - Make this a still shot with a voice over. To do this, take a picture of your schematic and insert the picture into the video.
   3. Show where your areas of weakness based on the simulation
   4. Discuss whether you think that is where your bridge will break based off of the actual design.
   5. Show how/where the bridge will be fastened and tested
2. (5 points) = Record your bridge being tested in slow motion (if possible). This is important because you will want to reference this in when discussing how your bridge broke. The break must be clearly visible in the video. Try to capture where the bridge is breaking and discuss in your video if that break matches up with where you had flagged (red/blue) trusses.
3. (5 points) = This will be a reflection of where your bridge actually broke and why it broke there. Discuss tension and compression throughout the bridge and what led to its collapse. This is a reflection so make sure you discuss what you learned and what you would do differently. Reference your blueprint for this part of your discussion.
   1. Discuss which beams broke and if that matched your predictions. If it broke else where, why do you think it did?
   2. Where did you see tension and compression, explain how you knew.
   3. What would you do differently next time
4. (3 points) - Discuss your cost to strength ratio. Take the total cost to construct your bridge divided by the amount of force that it was able to hold.

Bonus points will be awarded to

1. Most cost effective bridge - your values in the video must match Mr. Goeldi's calculations.
2. Most creative video - points may be awarded to multiple videos that went above and beyond.
3. Most unique design that is able to hold some amount of weight.

A final peer evaluation will be given. (10 points total)

5 points Mr. Goeldi and his sub's evaluation of your time in class.

5 points for a peer evaluation.

Videos are due at the start of class on Monday, February 10th.

Total Project - 73 points