SW: Brücke 15DEC18 - 11JAN19

A Bridge Design Competition for my High School Engineering Class

Project Descriptor

Task: Design, build, and test a bridge structure with maximum efficiency.

Constraints:

• Bridge must span an 8 inch gap, and may be no longer than 12 inches.

• Bridges must be no wider than 4 inches.

• Bridge must be less than 4 inches tall.

• Bridge must provide a roadway to support a Modarri car (path must be clear and easy to traverse).

• All teams receive a $10,000 budget.

• Bridges may be made of the following materials:

  • 3D Doodler Pen Filament $1000 per stick

  • Balsa Sticks $200 per stick

  • Balsa Sheets $4000 per sheet

• Other costs:

  • Elmer’s Glue $500 per day

  • Super Glue $2000 per day

  • Laser Cutter (for Balsa Sheets) - $500 per cut (each time “play” is pressed)

• Bridge Efficiency will be calculated as a ratio of maximum load to overall bridge weight.

Utilize course tools to create and justify your chosen solution (MD Solids,Fusion 360, Bridge Designer, etc.)

Timeline:

• Criterion A: Inquiring and Analyzing (Interview 12/17)

• Criterion B: Developing Ideas (Interview 12/20)

• Progress Check #1 (1/7)

• Progress Check #2 (1/9)

• Criterion C: Creating the Solution (Interview 1/10)

• Bridge Testing Day (1/11)

• Criterion D: Evaluating (Interview 1/15)

To Do

• Design truss w/ Grooves for car to go under bridge

• Figure out how to test balsa wood in F360

• Test Structure

• Identify weak areas, re-enforce, test again.

• Check for Car Fit

19A04

Started designing the truss for the main part of the bridge. Bridge will be in a general triangular shape from a side view. Built up this webpage to store information on the project. Modeled already designed truss in Autodesk Fusion 360.

Truss Design

Chamfered each side to 60 degrees to allow for the triangular design of the bridge (force applied to edge will distribute load better than on a face)

See edges here

Joined 3 faces together for a proof of concept.

Triangle Truss

Bottom Truss will most likely change and a "runners" for the car to drive over. When I attempted to test the bridge there was no material in the program labeled "Balsa Wood" when I attempted to change some values for a different type of wood, I crashed the program and had to attempt to test it with the bridge being made of ABS plastic. This bridge (10 x 4 x 4) held almost 400 lbs of force when tested in my program. This makes me quite optimistic for our odds in the competition.

19A08

Today was the first day back in class. We found that the Modari Car will just fit in our triangle design. The bottom truss was designed and testing was started with stresses in F360.

19A09

Continued testing and optimizing components of the bridge for the competition.

19A10

Finalized design for the bridge after a small test. Generated PDFs were turned into Laser Cutter ready files using Adobe Illustrator. However, the file was too large (area wise) to cut today so cutting was deferred to A11.

19A11

Design was cut into the balsa sheets at a 40 degree angle to give it as much stability as possible. Edges sanded and superglued together. Bridge is now drying and preparing to be tested.

19A12

Bridge test day! Unfortunately our bridge did not work as well as we had hoped. While our truss was very effective in distributing the weight to the edges of the bridge trying to eliminate the support from the bottom cause the bottom to shear and break our bridge

Criterion D

1. Presents detailed data of bridge performance from test.

2. Critically evaluates the success of the bridge against the success criteria based on testing.

3. Explains how the bridge could be improved.

While the bridge appeared to flex quite a lot with the force, what eventually killed the bridge was us trying to reduce the weight as much as possible. With our bottom (road) cut out and not just a plank, the truss on the bottom eventually broke and took the bridge with it.

Data

• 0.046 lbs

• 6 lbs of force supported

• 130.4347826 Efficiency

Areas of Bridge Failure

II. Our criteria

1. Cost: The cost is determined based on the cost and amount of material used for constructing the bridge.

2. Weight: The weight is determined based on the properties of the material and the amount, the goal is for the bridge to be as light as possible.

3. Practicality: This criterion is based on how accessible is to build the bridge with a given time frame and its constraints.

4. Stability: Determined by how stable the bridge can stand either when applying a force on it or when static

5. Force Distribution: This criterion is determined by how the tension and compression is distributed among the bridge (mainly focused on the top and bottom of the bridge)

• Cost-wise our bridge was effective as we still had $1500 left and if given a chance to test then improve our bridge we could have further improved upon it.

• Weight: Our bridge weight was one of the lightest in the competition. This however, proved to be our downfall, for as we attempted to cut out too much weight and made the bottom of our bridge too weak to put the true truss to use.

• Practicality: Our bridge was very practical only requiring 1 day to cut and assemble. The true time suck came from the CAD and weighting for the printer.

• Stability: Our bridge, with an exception to the bottom was incredibly stable and when tested in fusion, without taking into account the bottom separating from the seam.

• Force Distribution: while a majority of our force was still focused around the middle; a large portion of it was shifted to other areas of the truss and increased its load bearing strength

III: Improvements

Our bridge could be improved by simply making the road a solid sheet of balsa or maybe two. This would remove the possibility of the bottom of the bridge separating from the rest of it.