The purpose of this exercise is to design and build a structure, which is capable of supporting a mass of at least 5 kg. or 11 pounds in the center of a span of 15 inches with the maximum width of roadway of 4.0 inches. The bridge design should achieve the highest efficiency possible.
The material that is to be used is #9 spaghetti (thin), which is to be supplied by the teacher. The structure must be three-dimensional and capable of fitting in the testing jig provided. Maximum points for the fabrication portion of the grade will be awarded for the lightest structure that will support the load. Bridges failing will be graded on the bridge’s structural efficiency (E). E=Max load supported/mass of the bridge.
Students will work in groups of no more than three and all in the group will receive the same grade (unless the group evaluates a member differently.) It is expected that the work will be shared equally.
In addition to the fabrication of the structure, each person will submit a one to two page report that will include all design drawings and calculations.
Students will also research bridge designs on the Internet and find one that fits their needs for the contest.
A bridge building program will also be used to construct and evaluate compression and tension members of the bridge design. The bridge building program will help students with efficiency evaluations.
Research:
Students can use books, magazines, and the library, to research bridge designs. The Internet will be used to find a web site that explains and demonstrates bridge styles and construction.
The students should include this information in printed form and attach to their report.
Bridge Building Program:
Student will make a drawing of the style of bridge they have selected.
The program will show compression and tension members and how strong they are.
A cost analysis and efficiency rating will be used to help students design and build their spaghetti bride.
Auto CAD Drawings:
A 3-D inventor drawing of each individual member, assembly, balloon drawing and presentation file, of the whole bridge.
The front elevation and side elevation of the 3-D drawing will be printed out and used as a pattern for the spaghetti bridge. The spaghetti can be cut exactly to the right size by laying it down on the drawing and cutting it.
Details about construction of the bridge:
Only spaghetti may be used for construction of the bridge. Any adhesive may be used to join the ends of the spaghetti. Longitudinal gluing may not be allowed.
No part of the bridge may extend more than ¾” below the support elevation.
The bridge length must be 15 long.
A hole must be provided in the center of the bridge to allow for the threaded rod. It is suggested that this area be strengthened to accommodate the point load.
The jig will be weighed and included in the weight on the bride. The bridge cannot weigh more that 100 grams.
Width of the bridge is 2.5 to 4.0 inches
No height requirement of total ht.
Max roadway thickness 1 inch.
Testing Procedures:
The bridge will be centered on the supports.
A bucket will be attached to the center support and the load will be applied. The student will add sand to the bucket until failure occurs. Maximum time for loading will be 5 minutes.
The weight of the filled bucket will be massed and used in the efficiency formula.
Failure of the bridge is defined as the inability of the bridge to carry additional load without breakage or sagging more that 1 cm below support elevation.
The Report:
The reports must have an introduction explaining the project.
It should have a procedure or step by step process how the bridge was constructed, materials used, and technique for construction.
It should include all calculations, formulas used, and math work.
All drawings, which included 3D and Bridge building program.
A graph of your efficiency rating.
Evaluation results and improvements made to design.
Conclusion explaining things learned during the whole process.
Bibliography page.
Title page.
Grading:
Research information (10 points) Individual
Accuracy Bridge/drawings (15 points) Individual
3-D Drawing Inventor (50 points) Individual
Building Program Drawing (20 points) Individual
Efficiency graph (10 points) Individual
Efficiency rating (50 points) Team
Report (35 points) Individual
Team Grades each persons work (10 points) Individual
Total points possible (200 points)
Time line (approx):
Research (1 day)
Bridge Building Program (4 days)
3-D Drawing (2 days)
Construction of Bridge (5 days)
Report (on own time)
Graphs and other (1 day)
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