Week 10: Duane

          In the previous week, the groups tested their bridges.  These bridges spanned about three feet.  Originally, the same design from the two foot bridge was used; just lengthened.  However, this did not produce the best results.  It was determined that in order to create a stronger bridge that spans three feet, the height of the bridge needed to be increased.  The bridge was modified completely.  The group tested this bridge on their own and determined that it too did not produce the best results.  It was contorting too much.  Once again, the bridge was taken apart and rebuilt, using part of the design from the very successful two foot bridge.  The bottom of both bridges have the same general design which evenly distributes the weight throughout the bridge.
          Teamwork was such a large part of this course.  Each person had a responsibility.  It was very important that each person had a say.  Each group member had a say in the bridge design and everyone contributed their ideas to make the bridge the strongest it could possibly be.  Documenting was very important.  Taking notes, taking pictures, and recording videos were very helpful when working on the weekly blog post.  Having the notes and pictures allowed for a better description of the progress made and also having pictures makes it easier for the reader to understand exactly what the design looks like.  Computer modeling such as West Point Bridge Designer provided very useful information about the group's design.  It provided forces and costs which allowed the group to modify the design to make it both stronger and more cost efficient.

A4: Breslin, Duane, and Ngov

BACKGROUND

The objective of this project was to design a bridge created from Knex pieces while considering the required constraints and parameters. The bridge needed to span a specific length while aiming to be most cost efficient. The efficiency was determined by dividing the total cost of the bridge by the total weight held. The first task in the bridge design process was to use computer software to get an understanding of to design a bridge. After information was gained, Knex pieces were used to create a bridge spanning two feet. Testing was done on the bridge to discover its strength. Following the testing, observation was done and calculations were taken. These results aided in the ability to lengthen the bridge to a span of three feet.

DESIGN PROCESS

Prior to the designing process, teams were established to set goals and collaborate during a ten week period to design the most cost efficient three foot bridge made from Knex pieces. Weekly progress was recorded on a team blog which showed a steady development of team work and design improvements. Many resources were utilized throughout the design process. The resources West Point Bridge Design, Knex pieces, Truss Analysis, and Bridge Designer were considered while creating the bridge throughout the entire ten week period.

The first asset used to aid the bridge design process, which spanned three feet, was a computer program called West Point Bridge Design. This program assisted students in understanding basic truss bridge designs, compression and tension forces, and the importance of cost. General truss designs of an arch, box, and under hang truss bridges were explored to allow groups to determine the most efficient design. A virtual simulation calculated the compression and tension forces of each member of the bridge. The greater the value of the force meant the member was weaker. This allowed for modifications to the design for improvement of the overall efficiency of the bridge design. In addition, different materials for members and gussets in West Point Bridge Design allowed students to consider the importance of cost. The strength of a material gave potential to increase the efficiency of the bridge while also raising the cost. Force and material were vital in the creation of a truss bridge throughout the Knex building process. This is because the ratio of the cost to weight determined the efficiency of the bridge. During the entire process, the cost of the design was extravagant. Consequently, the design was altered numerous times to decrease the cost while attempting to maintain the strength.

The next type of source that assisted in the development of the best bridge was Knex. Knex allowed a physical representation of how a bridge was built and failed. The construction with Knex pieces showed real life limitations. For example, the limited amount of members and gussets represented how manufactures do not have every size available for construction, while numerous fail factors can be physically seen. West Point Bridge Designer did not show geometric contortion like Knex. The bridge development through the use of Knex exposed vertical and horizontal failures while allowing failures to occur at multiple points on the bridge. This resulted in necessary changes to improve a similar example of a real bridge experiencing outside forces such as wind, earthquakes, and traffic. In addition, Knex allowed accessible and simple changes because every piece was readily available for modifications if necessary improvements were needed.

The following resource utilized was the concept of truss analysis. Calculations on the members of the bridge were calculated and the results were similar to the forces given from West Point Bridge Design. This reinforced the importance of improving the design at the weak members on the bridge to increase the efficiency. In addition, experiments with Knex pieces during the load testing allowed physical observations of the weakest members and contortion. The use of Bridge Designer also showed the weakest members of a basic bridge design. The disadvantage with the use Bridge Designer was the inability to input any design. The Bridge Designer program required triangular connections at every node. Nodes are similar to gussets in which they are the connections joints for members. The program did have an advantage where the general concept of any truss design could be applied and simply scaled. If the height was scaled by a factor of two, the forces of the members would decrease by roughly a factor of two.

In the final bridge created, every resource used was applied in designing the best possible bridge. The final bridge can be seen in Figure 1. The overall design was created after the observations of many bridge failures occurred during the load testing. Designs that did not include gussets with grooves appeared to withstand the most amount of weight. This resulted in using the least amount of grooved gussets; refer to Figure 2 for two groove gussets together forming a connection joint and Figure 3 to see a one groove gusset. The connection at the grooves would not fail as a result of weight but horizontal force. In addition, the cost was considered and determined that the use of the regular gussets had more of an advantage over the grooved gussets. Many sockets of the gussets held the maximum number of members possible to increase the pull out load and the load capacity. In addition, the height was increased to allow the forces to evenly distribute. The goal of the bridge was to create a design that would fail as a consequence of weight, not contortion or vertical and horizontal force. Throughout the improvements of creating the final design, the weakest members were constantly changed to decrease the force applied. After testing and considering prior resources, the predicted failure load was estimated to be at thirty-five pounds.

Figure 1: Final Design of Bridge. 

Figure 2: Two Groove Gussets Together.

Figure 3: One Groove Gusset.

FINAL DESIGN

            The numerous design attempts, research, analysis, and testings group one created a final design seen in Figure 1. The plan and elevation views can be seen in Figures 1 and Figure 4 respectively. After discussion and consideration of research, analysis, and testings, group one extended the height to eight and a half inches this is because it allowed more even distribution among all the members. In addition, the overall design from the previous bridge was kept because the strength and efficiency was effective. Also, the connection joints were altered because it was discovered that the gussets with grooves, as seen in Figure 2, was weaker then regular gussets without grooves. Another influential aspect was the design of the bottom of the structure. The cords on the bottom were pulled through the holes of the gussets to allow for more flexibility in the bridge; as a result, this allowed the bridge to withstand greater compression and tension forces. This cost and materials list can be seen below in an Excel spreadsheet in Figure 5. 

Figure 4: Plan View of Bridge.

Figure 5: Excel Spreadsheet of the Materials List.

The total number of Knex pieces used was 212 and cost $375, 500.

FINAL RESULTS
            The final bridge was tested by setting an apparatus on top of the bridge. This can be seen in Figure 6. Connected at the bottom of the loading apparatus was an empty bucket. The apparatus was placed as close to the center of the bridge to allow an even displacement of the weight throughout the members. The bucket was slowly filled with sand until the bridge failed. The weight the bridge supported until the failure was then placed on a scale to be found. In the final testing, the bridge spanned a length of three feet. This bridge was able to withstand a downward force of 32.2 pounds and failed as a result from weight. The weakest area of the design was at the reaction points of the structure.  Similar to the first design, the second bridge also had a graceful failure where the deflection of the bridge was visible. A bridge cannot be improved if it failed as a result of weight unless an entire design is created.

 Figure 6: Apparatus on a Bridge spanning three feet.

CONCLUSION
            The course showed how the process of designing a bridge can be applied to Knex pieces. After testing the bridge, group one was able to conclude that the bridge behaved as expected.  In terms of the final bridge, the failure was thought to be as a result of weight. The results confirmed this prediction as the sand was slowly poured into the bucket. The overall geometry of the bridge did not contort but failed as a result of the downward force of weight.  The failure point at a reaction point can be seen in Figure 7. The group knew after computer and computational analysis that the end points were the weakest parts of the bridge. The predicted downward force the bridge was expected to withstand 35 pounds.  After testing, it held 32.2 pounds giving the group roughly an eight percent error in their prediction. Different aspects of strategies in teamwork, calculations, computer testing, physical modeling, and physical testing were explored. The course allowed further development in each skill. 

Figure 7: Failure Point of Bridge After Load Testing.

FUTURE
            As a result of the testing, modifications could be made to improve the design of the bridges.  Members should be added to the side of the bridge in order to prevent the bridge from contorting.  In addition, more reinforcements towards the end of the reaction points would allow more even distributions in every member; consequently, the efficiency of the bridge would improve.  

Week 10: Amanda Ngov

Last week was the final testing of bridges. My group performed the load testing similarly to week 6. Sand was placed into a bucket that was suspended on an apparatus, while being hung at the middle of the bridge, until the bridge failed. No other alterations were made for the upcoming week because the course has ended. If goals were necessary for the next week, my group would have tried to improve the weakest point of the bridge at the reaction points to improve the efficiency of the design. This week was difficult because new designs were constantly being created to find the best bridge design out of Knex pieces. Discussions about our previous research was considered throughout the entire redesigning process. Different members suggested one design while other members preferred different designs and applications of the research done two weeks ago. In the end a similar design from the original was used after increasing the overall height of the bridge.

All topics that were intended for students to experience and learn from were presented in the course. Teamwork between my group, planning a sensible schedule, documenting the results of progress, and the process of designing and altering a bridge to improve the efficiency were taught. In addition, computer modeling in West Point Bridge Design, physical modeling with Knex pieces, forensic analysis of bridge failures, static analysis through calculations, and computer software were all utilized and vital in the bridge designing process of the course.

To be honest the entire class was beneficial because of the how hands-on experience. I do not believe that the class was a waste of time in any way. With this said, I believe that the class allowed students to focus on a real life situation on a scaled down version with different programs and kit. Also, I do not believe the class structure or curriculum needs to be altered.

On a side note, the website was extremely clean and easy to navigate. Use this for next year if the course will be available for students to take.

Week 10: Bridget Breslin

In the previous week, the team had redesigned the bridge completely for the thirty six inch span. The bridge was then tested during class. We had suspected that the bridge would hold somewhere in between thirty and thirty five pounds. After testing the bridge, it was able to hold 32.2 pounds. The efficiency cost was $11,599. I thought that the bridge would break in the middle due to the weight however it broke at the bottom side. Regardless the bridge held as much as had been predicted.

Looking back at the time spent in this course, I think that I really learned a lot. In every topic that was discussed there were elements that helped me to expand my thinking and understanding of how things work. At first, thinking about building a bridge out of Knex does not seem like a difficult task. However, it is a much bigger challenge. This course enabled me to think about how by adjusting part of the design, it could benefit or hurt another part. It also allowed me to understand real life situations a little bit better. Thinking about everything completed and used throughout the course, everything seemed to be beneficial. The software used helped students to get an understanding of how a bridge works but also to think of other factors that may not be as obvious when constructing a bridge. Even all of the people that were involved in the learning process were extremely helpful and excited about the project. This helped student to understand the task at hand better and become more excited to find out how everyone will do. I think the most beneficial thing for me was experimenting with the bridges. Being able to physically see what was wrong with the bridge gave me a better idea of how it should be adjusted and how the bridge actually works. Overall, this section was very educational and fun which made it easier to learn.

Week 9: Bridget Breslin

In week eight, the team’s main focus was to expand the bridge. The initial plan was to keep the original design of the 24 inch span and to adjust it to reach a span of 36 inches. After testing this design and modifying it many times, the team was able to conclude that this plan would not work. After much observation and discussion it was decided that the team would have to start from scratch with a new design. The new design for the bridge has an increased height. The bridge is much taller than was originally planned. However, even though the bridge was completely redesigned, many elements that appeared to be very successful in the old bridge were incorporated. The new bridge is more expensive, however is likely to hold around 35 pounds.

            Now that the term has come to an end and I have had more experience with bridge building, I have learned many things. One of the main things I learned is that building a bridge is not an easy task at all. There is a lot of thought that has to go into designing a bridge. Also, a design that may work in one instance many be a terrible idea in another. Each scenario is different from the next. However, looking back at styles and techniques of preexisting bridges can aid in the design of new bridges. Simple concepts seem to work extremely well, it is not necessary to get extremely fancy unless it is needed. Bridge design also forces you to think of how the entire product will be affected by one move rather than just one specific area. A bridge is an entire unit that relies on each member to work successfully.

Week 9: Team Update

In the previous week, the group worked on extending the bridge from a twenty four inch span to a thirty six inch span. This task turned out to be much harder than it was anticipated. The team initially decided to keep the original design of the twenty four inch span and to expand the bridge using the same pattern. After testing this idea, there was little success. The team then added and took away many different aspects of the design only to lead to failure. Each trial resulted in the bridge only being able to hold approximately twenty to twenty five pounds.

            After much review and consideration, it was determined that the bridge needed to be completely redesigned. Although the design for the twenty four inch span worked very well, modifying it to reach thirty six inches would not work properly. The new design is quite different but has many of the same elements. The bridge is a lot taller than the first design was and included many different types of structure beams on the inside of the bridge. However, some elements that remained the same were the thickness of the bridge, the use of triangles, the technique to allow bending and beams used on the sides of the bridge to minimize contortion. This design for the bridge costs about $373,500 and can hold potentially thirty five pounds.

Week 9: Duane

      In the previous week, the group extended the bridge that spanned a total of two feet to three feet.  The group kept the same design, and only modified the length.  The two foot design held 47.8 pounds, the same design, just a foot longer held only 28 pounds.  Not what the group was expecting to see.  However, I did notice that many other groups were observing the same results when testing their bridge.  So modifications were made.  The group tried to keep some details of the strong, original two foot bridge in the three foot design.  Some modifications include increasing both the height and width of the bridge.  While designing and testing the new bridge, major twisting was noticed and was at fault for the failure.  Once again, modifications were made to prevent the bridge from twisting.  While testing the newest design, there was very minor twisting noticed, and the bridge was failing because of weight and not twisting which was what the group was looking for.  One thing to keep in mind, while testing the bridge some of the pieces actually broke under the weight.  Pieces included the blue gusset plates.
      I have learned many things about bridge design.  Especially that it is a lot of "trial and error".  You are constantly testing designs and then making necessary modifications and then testing again.  There are many programs available to help in the design process as well.  A program such as West Point Bridge Design is very useful because it shows the tension and compression forces on each specific member of the bridge and can help to identify any weak parts of the bridge.  With calculations, the forces on a bridge can be computed.  This leads to the design of a much stronger bridge.  Finally, I also learned that when designing a bridge attention is not only focused on the strength, but also on the price.  This is very important to realize because the government or a company usually will have a budget for you to work within.