Week 9 Post

At the beginning of class next week, the group began to look into designs of what may work for the 3' span. Shortly thereafter,we began to build a 3' long bridge based off of the 2' bridge design. What we came up with was a working but somewhat disappointing bridge to our standards. We tested the design twice during the class period and ended up with a load of roughly 32-36 lbs. after a few minor tweaks.  At the conclusion of both attempts, the bridge failed in the middle. If we were to include a cross section there, we would not have been able to place the weight bearing mechanism directly in the middle of the bridge span.  I, as well as Gary and Izzie are expecting great achievements during Week 9's testing. I have learned a great deal of aspects of bridge designing, not only in 2-d but 3-d as well. The force distribution was a very cool process to go through since I am a very math intensive student.  Having some slight background with bridge and cantilever designs back in high school really helped me prepare for what has already and is to come in the ENGR 103 course.

Weekly Post (week 9)

1. What you did in the prior week
In last week, I helped our group expend the bridge to 36”.  I discussed how to improve the bridge maximum load of the bridge with my group mates. I observed the failing process of the bridge and tried to fix the weakest spot of the bridge.

2. What you and your teammates have agreed you'll do in the coming week
In the next week, we will take our new bridge to participate the competition two. We will finish the final report which concludes the process of developing of the bridge.

3. Major accomplishments of the week for the team
Due to the excellent performance of the design of the last bridge, we decided to follow the original design on the new bridge. We used the 2-1/8” long chord to replace the 1-1/4” long chord in the original, and used the 3-3/8” long chord replace to the 2-1/8” long chord in the original. The size of every piece of the bridge has been enlarged to the next size. It is an efficient way to expand the bridge

4. Issues that the team or you as an individual faces
We still not found out a perfect solution of the weakest spot in the middle of the bridge. What’s more, the final exams are coming and everyone is busing preparing the final. At the same time, the whole team should work efficiently to finish a high quality report.

5. You've now almost completed the bridge design process for the term. What have you learned about bridge design specifically?
I have learned how to turn a design from the 2-Ddrawing to 3-D reality. Any designs need a clear and organized plan. Knowing the constraint, and develop your design based on the constraint. It is important to understand the academic basic of the design. It could help you to find out the weakest of the design theoretically, such as the compression force applied on the bridge. However, theory is different from the reality. The design should consider many other factors beyond the theory, such as the twist of the bridge in reality.

Week 9 Post

Last week in class we used our 24" bridge as a starting point for the construction of our 36" bridge.  We finished constructing the bridge and we tested it out two different times.  We had a similar problem both times.  The bridge kept failing in the middle, mostly on top.  We did not have a triangle up there because at first we wouldn't have been able to fit the hook through the top, and then we wouldn't have been able to add any weight onto the bridge.  However, at the end of class I found a way to form triangles on the top while having the hook fit through the top of the bridge.  This should hopefully allow our bridge to hold more weight as it will keep the middle of the bridge more sturdy.  We will make this addition during our next class.  We will also be officially testing our bridge in the contest next class.  We can only hope for the best.  So far our 36" bridge has been able to hold 32 lbs.  I am hoping we can try to near somewhere around 40 lbs this time.  Holding up over 30 lbs last week though was probably our major accomplishment of the week.
I have learned a whole lot about bridges from this design lab, especially since I knew nothing about building a bridge previously.  The one thing I learned the most about was compression and tension.  I learned where most of the tension and compression are on the bridge and the importance of the ratios for each beam.  WPBD probably taught me the most as it gave me the most information on my bridge while I was building it.  This has given me great insight on how to build a bridge, and hopefully this knowledge can help me build other structures in the future.

Weekly Post (week 8)

1. What you did in the prior week
In last week, we did the truss analysis in class. Through the guide line of the online resources, we learned how to do the truss analysis using the joint method.  Triangle calculation and free body diagram are the most important parts of the method of joints.

2. What you and your teammates have agreed you'll do in the coming week
In the future weeks, we will prepare for the competition 2, which is the final competition. We will record the process of competition for the final lab report.

3. Major accomplishments of the week for the team
We understand how to identify the compression force and the tension force. It will be helpful in our future bridge improvement. The online bridge designer provides an idea that the scale of the triangles greatly impacts the force working between triangles.

4. Issues that the team or you as an individual faces
We still have a lot of assignment to complete in the future two weeks. We will try to improve our bridge using what we have learned from the truss analysis. And we need to finish the A4 report which is important for our final grade.

5. You have now experienced one form of analysis. Address the following questions about it considering your Knex bridge:

• Is that method of analysis sufficient for a real bridge? If not, why not?
It is not enough for a real bridge. We discussed the difference between WPBD between real bridges before. The truss analysis of what we did just in two dimensions. But for a real bridge, it needs to be considered as three dimensions. A real bridge has to take force from wind. And the load would not only apply on the center of the bridge. Emergency situations should also be considered.
• What further would you like to analyze and what knowledge or tools might assist you?
The force applying on different material will also impact the performance of the bridge. And the force apply on joints should also be analysis the increase the performance of the gusset plates.

A3-Ye

1. Using the configuration shown in the drawing at the bottom calculate the forces in the truss members using the "Method of Joints" with h & W as defined in the constraints below. And Using the results of the previous truss analysis create a diagram similar to the one below with the forces next to the members or in a table on the diagram with member-to-member (e.g. "C-D") labels

2. Using the online Bridge Designer replicate this analysis

3. Define what you have to do to make the results of the hand analysis correspond to online Bridge Designer


The result of the online Bridge Designer is similar to the hand analysis of part one. The difference is cause by the different scale between hand analysis and online Bridge Designer. The length of the member has been given in the part 1. But the Online Bridge Designer does not have the function that calculates specific number. If the triangles of the online Bridge Designer have the same angle with the triangles in part 1, it should give the same result number.

4. Use the online Bridge Designer to model your Knex Truss

             
5. Define in words how you might use this type of analysis to improve the design your bridge given the testing information about Knex Joints in this web page


The weakest point of the bridge could be found by the truss analysis. Additional piece could be apply on that point and increase the maximum load of the bridge.

A3-Reiff

1 & 2.

The professor posted this morning that all of the units should not be in the metric unit.  Currently all of my forces are measured in lbs m/s^2 as I incorrectly converted my forces from pounds to newtons above.  In order to have all of my forces in the correct units of pounds I must divide the force of each member by 9.8.  This will give me the correct force on each member in pounds.

3.

4. The results from the Truss Designer Program and the hand analysis are close to each other.  The major problem between the two is the scaling.  I was only able to use increments of 5N when defining the forces, so some of the forces were not exact in the Truss Designer program.  I converted the 20 pounds of weight to newtons so it could be used with proper units in the Truss Designer program.  However, the biggest problem was that the numbers were not scaled correctly between the Truss Designer program and the hand analysis.  This was most likely the biggest problem encountered.

5 & 6.

The biggest difference will probably be the weight of the bridge made out of knex compared to this bridge, although this bridge is roughly the same design as our knex bridge.  Last time we tested our bridge the truss that failed was in the middle of the bridge.  This can be seen by looking at the analysis above.  The middle is clearly under the most stress.   While support could be added, that could end up adding more weight to the entire bridge, changing the calculations that were just preformed in this analysis.  The best part about this analysis is that I can see where the bridge is most likely to fail, and I can figure out a way to solve this problem with my fellow group members.

Week 8 Post

Last week we listened to Professor Mitchell explain to us how to find the different forces throughout the bridge when a single weight is suspended from the middle of the bridge, like it is for our competition.  After that we started working on the Method of Joints in order to complete the Truss Analysis that will be completed soon after this post.  We finished most of the calculations in class, but sadly there was not enough time in class to finish all of the calculations.  In the upcoming week our group plans on using the tools we have learned over the previous week plus everything we have learned in this lab so far in order to build a 36" bridge.  The major accomplishment of the week last week was almost finishing the Method of Joints.  That was very clutch.  We are currently not having too many problems.  The biggest problem we have to fix is with our bridge design.  The middle sways too much and is too vulnerable, as the Truss Analysis this week has shown.  I plan on supporting the middle of the bridge better to fix these crucial problems.

The method of analysis is a great step in the right direction for a real bridge, but it is not sufficient.  Scaling is one big problem, and it will be discussed in greater detail in my A3 post.  Also, some of the materials will weigh differently, and a different weight could be suspended from the middle.  While corrections to calculations can easily fix these problems, it's a hassle and there has got to be a more efficient way to analysis the trusses and use this analysis to construct a more efficient bridge.