Modified K-Truss

I am sophomore at Adlai E. Stevenson High School and this is a truss that I made in class. We went through the engineering design process to make a bridge that would be able to hold a weight that was at least one hundred times its own weight. This bridge is a K-truss that I had selected through research and I had modified it as well.

I used wood glue as the adhesive, thin strips of balsa wood for beams, a wood angle cutter to make precise cuts, notecards to act as gussets in the truss, and Inventor to make designs.

I will be using inventor to design a truss bridge that is structurally sound and able to be tested in Inventor’s Stress Analysis software. I will be using the frame generator tool to create a 3D model of a truss design that will be the basis for your physical build of the Balsa Truss Bridge.

Physical Constraints to Consider:

• Must be able to span 16”, be 2.5” wide and be </= 6” tall
• Must hold a block that will be placed in the middle of the bridge deck
• Bridge can’t have laminated beams except lower/upper chords. Truss must be single plane

Inventor Constraints:

• Any sketches for the truss design must be fully constrained
• Bridge should be assembled and fully constrained for Stress Analysis using a block to apply a load
• Stress Analysis must be completed, without errors

Research Findings:

Pratt Truss

Advantages:

• simple to build because it has fewer members than most trusses
• easily adaptable since it's structural behavior is easily understood

Disadvantages

• easy to mess up build which will be extremally detrimental to the build
• not ideal for vertical loads and shear loads (loads going against each other: side to side)

K Truss

Advantages:

• reduced compression because it has self supporting members compared to other trusses
• reduced bending in horizontal members compared to other trusses

Disadvantages:

• more complex than Pratt truss
• more labor to build

After balancing the advantages and disadvantages, I ended up choosing to build a K-truss. First I built the truss in Inventor (https://drive.google.com/file/d/1G9ZAH5bxS_iyvMILMOgkPcM9hGFtgqfu/view?usp=drivesdk), then I made an assembly (https://drive.google.com/file/d/1G9ZAH5bxS_iyvMILMOgkPcM9hGFtgqfu/view?usp=drivesdk) to get a stress analysis on the bridge.

After looking at sample in class I decided to modify my current design of the K-truss in inventor and then I made an assembly to get a stress analysis (https://drive.google.com/file/d/1G9ZAH5bxS_iyvMILMOgkPcM9hGFtgqfu/view?usp=drivesdk) on the design and ended up with a lower maximum displacement going from a 0.02572 inches to 0.02245 inches. The displacement decreased by 0.00327 inches which is huge when considering the overall displacement.

1. I printed out an assembly title block with my build inside of it in order to build each phase of the build on the printed sheet
2. I cut out the necessary pieces from balsa wood for making the build with an angle cutter
3. I cut the notecards into small squares to have as gussets for the truss
4. I placed the balsa wood pieces onto the printed paper into their respective places and taped them down
5. After taping it all down I used wood glue and gussets to connect the pieces and keep them strong
6. I attached a side and the top to each other using glue and used wood clothes pins to keep both sides attached to each other while drying as it takes around 2 days to completely solidify
7. I attached the other side to the bottom and did the same thing as I did to one side and the top
8. Finally I glued and used clothes pins to attach both sets of sides to each other

In class we used a structural analysis machine to cause a load pulling downwards on the truss. My final build measured to be 32 grams. When put in the machine and tested it was able to hold 22 pounds leading my build to hold around 310 times its weight which surpassed the goals that needed to be met for a successful build.

After building this I learned that I should reflect upon previous topics that I have learned of or research more efficiently to build the most efficient truss, however this does not only apply to trusses. It is a great idea to look back upon ideas you have learned in order to ensure success. During the actual build, after I finished making the sides, I realized that I should have thought about which way each side should be glued and not look at how quickly I can finish something if I glue it a certain way. The first part that broke during the time the structural analysis machine was used, was one of the side beams which was not predicted tp break first, rather it was less likely to break than the other major pieces. Yet it did break because of the incorrect positioning of the bridge when building. In the real world, making bridges/trusses and other architectural models/structures, forces must be considered and how we put them together matters because without it fatal mistakes can occur. The major takeaways of this build that can be used in your day to day lives includes that everyone should take time to look at what they are doing and use previous moments and ideas from their lives and the lives of others in order to make the nest decisions.