Constraints

There are many specific constraints for this project because it has to go to competition and has to follow a lot of rules. Listed below are some of the major constrains for the design.
  •      • The bridge must be easy to build and cannot take longer than 45 minutes to assemble.
  •      • The bridge should weigh less than 400 lbs. If it weighs more, then the overall score will be marked down significantly.
  •      • The bridge must only deflect by 1in laterally and by 3in vertically.
  •      • All of the parts of the bridge are going to be donated. Therefore, as we create the design of the bridge we have to take      into account what various materials we might actually end up using. We cannot just design for what we would want our      ideal material to be.

    • Design Alternatives Options and Decision Matrices

    The four different bridge designs that were analyzed using RISA 3-D were the Pratt, Howe, Double Warren, and Baltimore bridges.
  •      • Lightness was determined by the length of all the members added up. If one bridge has a longer total of steel, then it      will weigh more.
  •      • Deflection was rated by using RISA to solve for the actual deflections under certain weights that are located in various      spots of the bridge. The maximum deflections were compared for the decision matrix rating.
  •      • Aesthetics was based on our team’s opinion of which bridge is most pleasing to the eye.
  •      • Time was based on the number of joints that each bridge has because these are the spots that will have bolts put      through them in competition. Thus, the number of connections effects the time of construction.
  •      • The strength of the bridge was determined by using RISA and getting the maximum tension and compression forces in      the members. The bridge with the lowest maximum forces, received the highest rating.
    • Alternatives

    Details and final design

    The final design that was chosen, using the decision matrix, is the Pratt bridge design. The members will be a 1” by 1” hallow structural steel (HSS). The thickness of the members has yet to be officially determined. The connections will be connected by plates on only two sides of the member. There for only one bolt will be needed rather than two. This will save assembly time for competition. The theme for our bridge is Northern Arizona University school spirit. Thus our bridge will have blue and gold coloring when it is painted. We chose this theme because we are proud to be representing our school and we want to show that we have a lot of pride.
    Final

    Gantt chart and internal team budgeting/time keeping (tasks vs. hours for each student/role).

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    Project Schedule
    There are five roles that represent all of the different tasks that will be done. The five roles are a senior engineer, another engineer, a lab technician, a fabricator, and a construction worker. Each of the group members will play these roles, except for the fabrication role because that will be done by an actually steel fabricator. The Gantt Chart shows the time frame for each of these tasks.
  •      • The tasks for a senior engineer are research, design, looking over fabrication results, overseeing construction, being at      conference, and reviewing documents.
  •      • The tasks for the engineer are research, design, checking fabrication, doing construction, competing at conference,      doing undergraduate presentations, and writing documents.
  •      • The lab technician designs using computer programs, does material testing, and checks fabrication.
  •      • The fabricator will do all the fabrication of the bridge, such as welding, drilling, and cutting.
  •      • The construction worker will do research to follow the rules, will do construction practice, and will do construction during      conference.
    • Chart