Bridge Design - Hudson

This term I learned a lot about bridges that I never knew before. I learned about different types of bridges - truss, suspension, etc. - and how these bridges work and I learned a lot about bridge failure along the way.

Through the use of the West Point Bridge Design software I learned about tension and compression and how bridges work in general. I learned how bridges were likely to collapse and what bridge designs wouldn't work at all due to they way they were constructed.

Through the use of Knex I learned that sometimes the way you model bridges isn't actually how the bridges will turn turn out and the way you predict failure isn't always how the bridge will actually fail. I learned that some bridges can look simple and be deceptively strong, and others can look strong but break under the slightest pressure.

The most important part of bridge designing, though, was doing the actual analysis and using Physics and Trig to figure out how the bridge would break, how much weight would be distributed where, etc. Even though WPBD gave all of these numbers, without context it really made no sense. I could tell you where the bridge was going wrong, but I couldn't tell you why. Doing the actual analysis helped me see how it all works together to make the cohesive product.

This week I hope to have our bridge do well in testing - hopefully over 30 pounds or the modifications would not have been worth it. Our bridge nearly doubled in cost but I don't know if the ratios will be any better considering we had an inexpensive bridge before that held 18 pounds where as much more expensive bridges could only hold up to about 40.

Next week I look forward to doing my final assessments on what I did and learned throughout the term.

Bridge Process - Lester

There are a lot of factors to consider when designing a bridge. West Point Bridge Designer seems simple, but almost all of the initial designs I made ended up failing even though they appeared to be structurally sound. After some practice, I discovered which designs worked and which did not, which designs were strongest, and which were most expensive. Using Knex was a whole other process. I learned how different the Knex materials were from the ideal ones in WPBD. Our design changed drastically throughout the process. We created a design using the process of elimination; if a program had existed it that could accurately model Knex-piece trusses it would have been extremely useful. Unfortunately, one did not exist, so we had to conduct hands-on trials. These trials were also informative, as we figured out which part of the bridge would fail and we used that knowledge in the subsequent design.
Engineers have to be very intuitive when designing a bridge. Something may look nice and add up to be inexpensive, but in a real trial it would fail much sooner than desired. In the truss models I had to take into account member strength, force/strength ratios, joint failure points and weight distribution. Free-body diagrams were useful in finding how much force would be applied to each joint. This knowledge is impossible to know unless the free-body diagram process, sometimes called Method of Joints, is carried out. It is a simple process but gives extremely useful information. I learned that different programs test different aspects of the design process and it is important to incorporate the best aspects of those programs in ways that fit with the intended medium (for example, WPBD designs using Knex pieces). At labs suring Weeks 9 and 10 we will test our final design and compare it to others in the class. I am not sure how much this new design will hold, but now that I have knowledge of where a bridge tends to break and how, I think this design will hold far more than our previous one.

Learned-Durkin

          During this process I learned about the many aspects of analysis necessary to build an efficient bridge.  I also learned about the many limitations of various bridge design programs and analysis procedures, such as West Point Bridge Design and Methods of Joints Analysis. During this class I was informed of the many different failures of bridges in the past and the differences between a graceful and a disastrous failure.  As a class and as individuals we gained the knowledge of the causes of these failure, the points of compression and tension where the bridge was weakest.  We gained the skills to do at least a basic analysis of the tension and compression forces on the members of our own individual bridges. This analysis as well as looking at a past test of K’NEX joints taught us quite a bit about what makes a K’NEX bridge more stable and what is just not a practical design.

            During last weeks class my group decided to completely redesign our bridge. We found that although our bridge worked fairly well at a span of two feet it was not a reasonable design at three feet. Due to the information shown online about the weight that can be held versus the number of member per joint we also decided to change the types of joints we used.  Our final decision was to make the bridge taller as we felt that this might help compromise the increased span.  Since then we have tested our new bridge and found it to be a much more efficient bridge.  The new bridge is much more expensive than our previous bridge however the increased carrying capacity makes it worth it. We plan to test our bridge again during the next class period as hopefully it will prove to be more efficient.