Truss Design 02

The second part of the final project for EK301 (Mechanics) consists of a preliminary design -- or, rather, several preliminary designs and one identified draft.

Having the data from the straw lab test and the resultant code to determine the approximate load that a straw can hold based on its length, it took quite a bit of creativity to find the perfect combination of straws. However, to simplify this process, the class was instructed to use a MATLAB code that would take a design and then indicate which member of the truss would fail first. It is important to note that all designs were given the same parameters:
Figure: One of two designs selected

  1. The truss must be a single, planar, simple truss. 
  2. Members must be joined concurrently at joints using the provided pins and double pinned to the guest plates. 
  3. Gusset plates may be any geometry but must have an area of less than 16 sq. cm.
  4. All joint-to-joint distances must be at least 10 cm and no longer than 16 cm.
  5. The truss must span a distance of 53.0 cm ± 1 cm.
  6. The truss should be designed such that it is supported and loaded in an “inverted” arrangement.
  7. The truss must support a minimum load of 4.90 N for 60 seconds. 
  8. The load must be located at a horizontal distance of 22 cm ± 0.5 cm away from the pin joint.
  9. The total (virtual) cost of the truss must be less than $350: Cost = $10 J + ($1/cm)L
To ensure that the code we created to analyze all of our draft designs is correct, the class was given a practice truss problem for which we were given an answer. The by-hand analysis should match the programmed analysis. I, being a bit of physics geek, took on the by-hand analysis for all of our team's designs, and another teammate Huiru took on the challenge of creating the MATLAB matrices. 

After we were sure that our code was perfectly arranged, we tried to crank out many sample designs as possible in order to find the most robust one possible (based on our strength analysis from the straw lab). We decided to prioritize maximum strength over cost efficiency, eventually agreeing on two preliminary designs that we then discussed in the final report.

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