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.

Week 9: Amanda Ngov

The previous week allowed my group to focus on improving the bridge more. We tested different types of designs with different members and realized that the design needed to be improved on dramatically. Although we were able to create a design that held 30 lbs on a three feet span, we wanted to create a more efficient bridge. Consequently, we decided to change the entire design for the upcoming week. Research on methods to improve any type of truss design during the week was taken to consideration while recreating a bridge. It was noted that more members attached to the gussets allowed a higher weight load for the bridge. The difficulty during the reconstruction of the bridge was finding a starting point. Some members of the group were unwilling to recreate a different design because the original design did extraordinarily well during the load test, but others were willing to create the most efficient bridge. After discussion, the group decided to create a new design and test it. The design that held less weight then the new design would not be used.

In this overall experience of designing and creating a bridge, I learned how tedious the process can be. One computer program or kit can be utilized; on the other hand, numerous resources, observations and research should be considered to design a bridge. New ideas are  constantly being discovered so research is needed to experience new materials or resource to create an efficient bridge. In addition, observations of other bridge failures and successes should be taken into consideration for designs. Also, there are pros and cons to any resource and tool to build a bridge. Computer programs can give numerical values and estimates of forces but hands on kit such as Knex can show how limited certain materials are to a purchaser. Lastly, research to find more design types or methods of improving a design is vital. Discovering a site where people have done studies on number of members used in a connection joint helped my group in creating the final design. The process has shown me to explore numerous methods of designing a bridge and approaching an idea.

Comp 2: Breslin, Corey, and Ngov

Group 1 from section 035 has come to a final decision for a truss bridge. After many deliberations, experiments, and observations it was decided that a new idea for a bridge was required to make the most efficient bridge. The bridge now has a few more connection joints and many more members to allow a more graceful failure. After research and observing other bridges' failures, it appears that the failure will occur on the ends of the bridge near the reaction point. It is believed to be towards the end because there is extremely little support compared to the other connection points on the bridge. The total number of pieces used are 212 and the total cost is $373,500. It is believed that the bridge will hold roughly 35 lbs.

Week 8: Duane

    In the previous week, the group completed two tasks.  One, analyzing the forces on the members of the bridge.  Two, lengthening the bridge.  The bridge was converted from a two foot long design to a three foot long design.  One problem noticed when testing the two foot bridge was that it was just two feet, giving the group a problem when trying to place the bridge on the supports.  This new design is approximately three feet seven inches in length.  Having the extra inches will be very helpful when positioning the bridge on the supports. Analyzing the forces of the bridge was no easy task.  However, it is extremely helpful when you know the forces.
    Knowing the forces on each member is very important and crucial to make the bridge the strongest it can possibly be.  This method of analysis will be very helpful in making the group's bridge stronger.  Knowing the forces on each member will allow the group to strengthen those members.  This method is also time-saving, the group can determine the strength of the bridge without physically testing it.

Week 8: Bridget Breslin

In the previous week, the group had worked on two different aspects of the bridge project. The most difficult part of the week was analyzing the forces that were acting on the bridge. Calculations were completed to understand the mechanics of the bridge and get a better idea of how it actually worked. These calculations allowed our group to see the different weak points and strong points in the bridge structure. Having the calculations completed will allow the group to know exactly how and where to adjust the bridge to make it as strong as it possibly can. The group also worked on converting the bridge from its original two foot design into a three foot span design. The new design for the bridge has to be able to extent over a length of three feet. We decided to stick the original design pattern, just adding more parts to extend the length. After this was completed the bridge now has a length that is about three feet seven inches. Making the bridge longer allows for more leeway to position the bridge as needed during testing, whereas in the last test the bridge had a length of just about two feet, making it difficult to configure against the supports. I think in the upcoming week the team will have the greatest problem figuring out how to apply information gained from the analysis to improve the bridge design.

I believe the method of analysis used is extremely helpful. It allows one to see the strengths and flaws of the bridge without having to physically test it. The method of joints seems as if it would be sufficient for a real bridge, however would be more complicated. This method could be used to see how strong the bridge is and by using prior knowledge of bridge failures and the materials of the bridge one can make predictions of how the bridge design would work. However, further knowledge of location of the bridge would help to make better predictions. Factors of nature could affect the function of the bridge. Wind, rain, earthquakes and other types of natural disasters can cause a change in the forces on the bridge; having these numbers will help to make a better analysis.

A3- Truss Analysis: Breslin

To determine the forcing acting on the member of a bridge, the Method of Joints was used. In this example the height is 6 inches, the length was 24 inches and the weight of the load is 10 pounds.

Below is a diagram of the diagram of the simple Truss Bridge with a table of the Member to Member forces.

After completing the analysis of the simple truss bridge by hand, a program called Bridge Designer was used. This program allowed the computer to determine the areas of tension and compression in the bridge.   The figure below is the result of the simple truss bridge in Bridge Designer. The red lines represent tension and the blue lines represent compression.

The results of the hand analysis match the results of the Bridge Designer analysis. When recreating the analysis in the Bridge Designer, it is important to make sure that the bridge is to scale. The bridge in the computer program must have the same dimensions in order to calculate the correct forces and produce the same results as the hand analysis. If the two do not match up then the bridge has not been scaled the proper way.

In the Bridge Designer program, there are specific constraints in the program which does not allow the proper analysis of the Knex Bridge. The program does not allow for the correct representation of the bridge structure. Without all of the members of the bridge being represented properly, the forces of the bridge in the program do not correspond with the forces in the actual bridge. Another important factor when calculating the forces on the Knex Bridge is to use proper scaling. Whether hand analyzing or computer analyzing, scaling is important to determine the correct forces.

The testing information about Knex joints can be extremely helpful when analyzing the bridge. By using the average strength of each joint in the bridge, one can use the Method of Joints analysis to determine how strong the bridge design is and then find ways to strengthen the regions of the bridge that are weakest. This type of analysis can help one to understand the mechanics of the bridge design and know how and where to improve the structure.

A3: Truss Analysis - Corey Duane

These are the calculations performed to determine the forces in the truss members of a bridge that has a height of 6", a span of 24", and a load of 10 pounds.

This table shows the member-to-member forces, a positive number means tension and a negative means compression.

This figure shows the screen capture of the bridge designer for the above analysis.

    To make the results of the hand analysis correspond to online Bridge Designer, you must design it to scale.  If the angles are different, then the calculated forces will not be the same so it is important to make sure that the size of each member on Bridge Designer is to scale with the members of the hand analysis.
    This type of analysis is very helpful and can be used with our Knex designs.  By using the measurements of our design, we can determine the forces and modify the design accordingly.

A3-Truss Analysis: Amanda Ngov

By using the Method of Joint, calculations for an analysis of a bridge was possible. Figure 1 shows the calculations of a bridge that has a span of 24", a height of 8", and a load of 15 lb at the middle joint.

Figure 1

The diagram and table of all the forces can be seen in figure 2 and figure 3 below.

Figure 2

Figure 3

A computer program called Bridge Designer has the abilities to create a similar type of analysis of the bridge with similar values as seen below in figure 4. The advantage of this program is that it has the ability to scale the values of the length, width or load of any type of truss bridge. With this in mind, the bridge in figure 1 can be drawn twice as small or large. The only needed adjustment would be to multiple or divide the results outputted by the program. For example, if my bridge had a span of 48", height of 16", and a load of 30lb then all the forces would simply need to be multiplied by a factor of two. The F_AB would be approximately -18 lb instead of -9 lb. This basic concept can be applied to a number of different designs. In addition, the bridge in figure 5 has similar features of the previous truss design but with extra beam members. When the design was drawn in Bridge Designer, an error occurred because certain nodes were not attached by members. This resulted in an indeterminate bridge, which forced my group to adjust the design in Bridge Designer. In reality, the changes would allow a shift and more even distribution of the forces onto the other members. The overall forces are symmetrically and evenly distributed, but the forces in my group's design allows more even distributions.The advantage with recreating the design in Bridge Designer is simple scaling of the weight load or the length of the members to different proportions.

Figure 4

Figure 5

The knowledge of the "Testing Information About Knex Joints" gives knowledge on the average, median and minimum force (in pounds) a member would pull out from a joint given the amount of members that were connected. It appears that as the number of beams connected to a gusset increased, the load capacity increased. The reasoning and logic behind the results is the force can be displaced more evenly throughout the entire bridge as opposed to a few weaker beams. In addition, if a member got pulled out of the gusset, then other members have the ability to allow a longer period of time for the collapse of the bridge. A more graceful collapse will occur instead of a catastrophic collapse. In real life, a catastrophic collapse could result in many casualties dying. The process of this analysis has shown a more even distribution of forces is preferable for n efficient bridge.

Week 8: Team Update

The previous week students learned how to calculate the applied forces that are exerted on the beams and connection points of the bridge. After first students were given resources to watch a video on how the calculations were computed. In addition, students were able to expand the size of the bridge from two feet to the size of three feet. In general, the majority of students furthered their current design because it appeared to be the most efficient bridge at the moment. The calculations of the beams and connection joints were found and were computed by Bridge Designer. It can be seen below in figure 1.

The upcoming week will include new ideas on improving the bridge after the design have been calculated. Different angles, lengths of beams, and connectors will most likely be changed because students will gain more knowledge about bridges.

Some difficulties that will seen will occur when the forces of the bridge are being calculated. Human error could occur during the calculations. In addition, certain changes may not be possible to occur because certain materials are not readily available.

Week 8: Amanda Ngov

In the previous week, calculating the forces of bridges was the main priority to improve upon the bridge. My group accomplished two main tasks. First we extended the two foot bridge to a span of three feet. We decided to keep the overall design of the original bridge because it was extremely efficient. Changes are still needed to improve the bridge after  calculations are computed. The calculations to improve the bridge was also a major task that was required and accomplished in lab. Since the calculations were figured out, the next week will become easier in terms of knowing which aspects of the bridge need readjustments. Changes in angles, beam sizes, and gussets may be changed to increase the efficiency of the overall bridge. A major challenge that my group and I experienced was difficulties in the calculations. Uncertainty in how to calculate the forces of each piece in the bridge was different and uncommon because my group and I were never exposed to a task such as this. The video on the resource site did help in understanding the concept more.

The overall idea of the calculations has a decent approach to figuring the force load of the bridge, but there are other outside forces such as wind, earthquakes, and traffic. Considering the bridge to be suspended without any other type of loads the calculations are sufficient, but the purpose of bridge is to allow transportation of objects from one side to another though. With that in mind, the analysis is not sufficient for a real bridge. If granted, I would suggest that further knowledge of the geography of the location where the bridge would be placed is required to reinforce the bridge at the weak spots. An earthquake for example would exert great forces on the connection joints. Wind, on the other hand, would create more forces on the side of the bridge. More knowledge of the population around the area is also required because a large number of commuters would result in a large load of cars and trucks. The geographical analysis and population density of the area, in my opinion, are vital in creating the most efficient bridge.

Week 7: Corey Duane

          In week 6, the group tested their bridge.  In the previous week, the bridge was able to hold 36 pounds. Minor modifications were made to stop the bridge from twisting.  The modified bridge was able to hold 47 pounds.  A video was taking during the testing in order to capture the failure of the bridge.  After close examination of the bridge and video, it was determined that the bridge did not fail because of twisting like in the previous week, but it failed at the end points.  After the test, the group further modified the bridge by removing some members that had effect on the strength of the bridge, resulting in a decrease in the cost.
          A major benefit of West Point Bridge Designer was being able to see and recognize any weak points of the bridge with "block box".  This allowed for the designer to quickly modify the bridge and correct any weak points.  This helpful tool is not available with the Knex.  There is no way to tell which members are under the most tension and if there are any major weak points.  With the Knex, the only way to find out these things is to test it and exam the bridge once it has failed.

Week 7: Team Update

            In the previous week, the team was able to see the bridge in action. The bridge was suspended across a distance of twenty four inches. An apparatus was then placed through the bridge with a bucket of sand attached to its end. The bucket was able to be filled about three quarters of the way full. This in turn meant that the bridge was able to hold 47.8 pounds. After minor adjustments to week five’s design, the bridge design in week six was able to hold 11.8 ponds more than its previous design. The bridge did not break due to the weight of the sand; it broke because of one of the end points. With more analysis and a few adjustments, the team will be able to stabilize the bridge and allow it to hold even more weight. The bridge design cost $207,500 and had an efficiency cost of $4,341.

            Adjustments must be made to improve the stability and cost of the bridge. The removal of unnecessary pieces from the middle of the bridge, the cost can be reduced by at least $10,000. The team must also discover a way to keep the end joints from slipping out of place. Fixing these issues can cause the total weight the bridge can hold to increase and the price of the bridge to decrease. A lower price tag and greater strength and stability leads to a much improved efficiency cost.

            In the weeks to come the team must transform the bridge from two feet long to three feet long. The biggest challenge is going to be tweaking the design to extend its distance. Not only does the team need to develop a way to make the bridge longer but also how that will affect the end points and all of the weak points of the bridge.  

Week 7: Bridget Breslin

In week six, the Knex Bridge that was designed by the team was tested. The learned a lot from witnessing the bridge in action. We expected that the bridge would do fairly well considering it had done well in week five. In week five the bridge held roughly 36 pounds. Minor adjustments were done to the bridge to stop it from contorting and it was tested again in week six. The bridge broke not due to the weight but due to one of the end joints. The entire bridge remained intact except for the end point it broke at. Overall the bridge ended up holding 47.8 pounds of sand and had an efficiency cost of $4,341. With a few minor adjustments and the removal of unnecessary pieces the team could greatly improve the efficiency cost.

In West Point Bridge Designer, the team was able to view the weak points of the bridge with “block box” answers. This was extremely helpful when determining which areas of the bridge needed to be adjusted to make it stronger. When using the Knex to build the bridge, this feature is not available. Without specific numbers, it is more difficult to determine which regions of the bridge are under the most tension and compression. If these values were available it would tremendously help with bridge adjustments. Although the tension and compression of the bridge parts is not readily available, there are ways to calculate it. Drawing a free body diagram of the bridge could help to visualize which pieces are the weakest. Calculations from the free body diagram could then lead the team to determine the greatest tension and compression on the bridge.  

Week 7: Amanda Ngov What Want to Analyze

The previous week was an educational experience because the bridges were tested. Groups tested their bridges by adding sand into a bucket, that was suspended by an apparatus, until the bridge failed and collapsed. As the sand was being displaced as evenly as possible into the bucket, students observed where the weak points of the bridge were. For example, a specific bridge did not fail as a result of the weight of the sand but instead failed as a result of a weak beam without much support. Towards the collapse of the bridge, students realized the bending of a Knex piece was in a great amount of compression. One of the end points that acted as the reaction points was a weak point because of the high amount of compression force. The upcoming week will result in further improvements of the endpoints. In addition the bridge will span from two feet to three feet. This goal originated from the previous week's lab where students were able to gain knowledge in other designs' failures. Difficulties will occur when the span of the bridge is required to span a minimum of three feet. The challenge with this obstacle will come from the lack of knowledge in the field and the weak Knex pieces. 

The use of Knex pieces has limited the ability to know the compression and tension forces of each beam, the amount of weight a bridge can hold prior to testing and the amount of deflection the bridge experiences during a point load are the three major questions that are constantly asked to try to maximize the efficiency of the truss bridge. The amounts for these numerical values requires calculations that are currently unknown to many students, if not all, because students have not taken courses related to bridge design.