Design Report

1. A written report is required for each K'NEX structure submitted for evaluation. The content and quality of the report will account for 50% of the project score. The remaining 50% of the project grade will be determined by the strength of the structure based on the ultimate strength-to-weight ratio (SWR). There are two strength criteria for structures: 1) all structures supporting the design loads (30% all-or-nothing); and 2) the structure with the highest SWR is awarded full points (20%) and the remaining structures will be awarded scores commiserate with their performance (first place will be awarded 20 points, second place 19 points, third place 18 points, etc. . .). If a structure does not meet the construction rules, listed below, the submitting student will receive no strength points.

2. The design report should include, but not limited to the following:

1. Title page - name, date and course information

2. Introduction - design and report requirements

3. Structural Design - a complete set of plans for the structure

4. Structure Analysis - a complete design and analysis of the structure including the force in each member for the applied load. Assume the modulus of elasticity of the K'NEX plastic is E = 377 ksi. Figure 1 show the typical cross-section of a K'NEX rod. The cross-sectional properties for this section are: I = 8.8 x 10^-5 in⁴ and A = 0.031 in². Also, include a prediction of the ultimate load of your structure. Show evidence that you refined and optimized your structure during the design process.

Figure 1. Typical K'NEX Rod Cross-Sectional Area

5. Summary - summarize the strengths and weaknesses of your design and give a prediction for the ultimate load and SWR.

3. All structural sketches should be produced using graphical software.

Construction Rules

1. Structures must be constructed using only K'NEX pieces.

2. Glue is not allowed in construction of the structure.

3. K'NEX members cannot be coated or treated in any way.

4. The structure must be designed to fit on the support shown in Figure 2.

Figure 2. Structure loading scenario and dimensions

5. The structure must cantilever at least 9 in. from the support. The height of the structure must not exceed 14 in. The height of the structure will be determined from the lowest point on the support to the highest point on the structure. The structure must be a minimum of 2 in. wide. A tolerance of 1/8 in. will be granted on all envelope dimensions.

6. The cantilever structure must include a connection to the support. In other words, your cantilever structure should connect to the vertical support wall. Figure 3 shows details of the wall connection.

   

   Figure 3. Structure loading scenario and dimensions
    

7. All structures will be loaded via a 3 in. by 3 in. loading block (see Figure 2) to the design load of 60 lb. or to the point of failure which occurs first. Failure is defined as the point when the structure can no longer support an increased load or collapse.

8. Each student may submit only one structure.

9. Structural performance will be measured by a strength-to-weight ratio (SWR) computed in the following manner:

         

where P is the ultimate load (lb.) and W_structure is the weight of the structure (lb.).

10. The cost of each structure will be estimated using the following cost sheet. A Cost Factor will be computed as follows:

             
    where Maximum Bridge Cost is the maximum bridge cost in the competition and Your Bridge Cost is the cost of each competitor's structure.
    

11. An adjusted SWR computed as SWR_Adjusted follows:
    
             
    

12. The structure with the highest SWR_Adjusted will win the event.

13. Any modifications or repairs to the structure must be done before registration. Once the structure is registered, no other changes may be made.

Schedule

This website was originally developed by Charles Camp for CIVL 3121. This site is maintained by the Department of Civil Engineering at the University of Memphis. Your comments and questions are welcomed.