Bell Weekly Blog- Week 10

In the previous week, the group tested our bridge in the competition. The results of the competition were that it held a total of 29.8 lbs, compared to when we tested this same design in week 8 which held a total of 35 lbs. The major accomplishments that the group has had this past week was placing third in the competition. Although our group didn't hold the most weight, we still had a decent cost to strength ratio. In addition to this, we placed first with the closest guessed weight and actual weight held. Throughout this term, our group has not run into any confrontations or obstacles.

After reading the course goals, I have found out that I have indeed learned many things worthwhile that I can still use later on. First of all, i have learned that teamwork is very essential. Without others, it would make it quite difficult to come up with all of the ideas by yourself. Planning the design was also crucial. Without planning, the building process would be quite difficult. It was also very important to document. Documenting everything made it very easy to refer to in case we needed any information. Probably one of the most important things that we learned was the design process. We learned through ourselves and other classmates the there are multiple designs that could have been built. A lot of thinking and brainstorming had to go into this process to try and come up with the best bridge possible. We went through this process both for the K'nex bridge and the WPBD program. WPBD was a very useful program that I used. The most beneficial aspect of this program was the numerical values that were given at each test. Once we tested these bridges, we were able to find out what was wrong with our design. We tested these K'nex bridges through truss analysis with forces on each member.I feel that the least beneficial aspect of this course was the blog posts. I felt that they had no other purpose other than for the sake of writing. However, this aspect does not include the A1, 2, 3, 4, Truss Analysis, etc., which were very beneficial. Setting the negative things aside, I feel that I enjoy this class as it is and feel no need to make too many changes to this course. The one thing that I would like to change would be the blog posts. Like I said, I think these posts are pointless and serve no meaning. However, this was a very exciting course and I am very pleased with it. 

Staquet Weekly Blog - Week 10

Last week in lab we got the chance to do the official test of our 36" K'Nex bridge.  Seeing as our group had full intentions of winning the competition, I was disappointed that the test results landed us in 3rd place.  During testing our bridge was able to hold 35 pounds but in the competition only made it up to 29.8 pounds before failing.  This was unfortunate but did however make our failure prediction weight of 30 pounds the closest prediction to actual weight held, therefore getting the group an extra credit point.  This week we plan to create the final report blog and submit it as our final assignment.

This term I learned a lot about not only bridge design, but all of the basic things necessary to make the design process possible.  I've gotten the chance to learn hands on about all the the course goals and see how useful each one truly is.  In general, the goals are a system of trial and error that are broken down into the proper things that go with it such as teamwork, planning, documenting, designing, and analyzing.  The group aspect made teamwork a necessity and planning was a must when making sure we were all ready for the upcoming deadlines.  Documentation was a must in terms of blogging, and helped to keep me on top of what was going on with the class.  I learned the design process is much more extensive than most people think and that it requires thinking about every last requirement and constraint involved with the build.  The analyzation of failures and overall bridge design is extremely important; it tells you which parts of the bridge need to be looked over and perhaps redesigned.  The least beneficial portion of this term had to have been the overuse of blogs and the constant comparison of the K'Nex bridge and a real bridge.  They are two entirely different forms of bridges that, in my opinion, should not even be compared when talking about the design and build process.  The most beneficial part of the class for me was actually building the bridges and getting to test them.  The sense of competition made it interesting, and it also gave me a chance to actually see the bridge fail.  Overall I enjoyed the course, but I really hated the blog, especially the whole double submission of assignments that I have already expressed my feelings toward.

Schetley Weekly Blog - Week 10

Last week in class we finally tested our 38" bridge. We expected our bridge to fail at around 30 pounds, and with a cost of $297,000, that would be a cost-to-strength ratio of a little under $10,000 per pound, which we felt would probably be one of the best ratios in the class. It failed because the weight became too much, starting to contort the bridge and it eventually collapsed (a video of that can be seen here). We actually expected the bridge to fail at the joints on the bottom like it usually did, so we weren't expecting that to happen. To stop that from happening, it would probably require us to strengthen the top of the bridge, or extend the top level of our bridge a bit farther across the bridge.

This being the final weekly blog post of this course, the weekly question we were asked was to look at the course goals listed on the class blog and discuss what we learned from each topic, what was the most beneficial, and what was the least beneficial of all the topics. I didn't really learn much about teamwork since I have been working in group projects since grade school, but I did learn a bit about each of the other topics, especially anything to do with the physical design of the bridge, such as physical modeling, and static analysis of the bridge. These were the most useful of the topics presented, as they provided me hands-on experience (in the case of the physical modeling) and an application of some topics I had been learning about for a while (when using static analysis). The latter answered the question that so many students ask: "Why do we need to learn this?" and that was very beneficial in my opinion. To me the least beneficial topic covered in the course was the topic of computer software. Looking back on it we used four programs: Blogger (which most people, including myself, already know), West Point Bridge Designer (a very basic bridge design software), Bridge Designer (an even more basic bridge software, this one doing load calculations), and Excel (which I knew how to use even better than Blogger before starting the course). This was also somewhat useless since most of these softwares we were introduced to for a week, then we moved on from them and went to work with physical bridges and physical modeling. If I could offer a suggestion, I would either change the amount of computer software lab lessons (I would make it less since I like working with my hands more) and remove the lesson on teamwork, because, as I mentioned, we've been doing group projects since roughly grade school so we should be quite familiar with group dynamics by now.

A4 - Section 35 Group 04

Below is the three previous assignments that each of us have done prior to this, detailing some of the steps we took to get to this final bridge:
A1 (West Point Bridge Design Bridge) - Bell, Schetley, Staquet

A2 (Individual 24" Bridge Designs and Cost)- Bell, Schetley, Staquet

A3 (Method of Joints Analysis) - Bell, Schetley, Staquet

Background:

Assignment 4 of Engineering 101–Bridge Design was for each group to design and construct a truss bridge using K’Nex which could be tested to determine its overall weight capacity.  The K’Nex pieces were each given individual prices and the group with the best bridge was determined based off its cost to weight capacity ratio.  The bridge had to have a clear span of 36” and be at least 3.5” in width.  A continuous clearing, 3” wide by 2” high, had to run through the bridge to simulate a roadway.  The bridge was tested by centering an 11” by 6” piece of plywood on top of the bridge; this piece was to act as a washer for a metal rod that ran through the bridge and suspended a bucket to be filled with sand.  Understanding how truss bridges are designed and how they react to stress  was an important aspect of this project and made it possible to build a cost effective bridge that could also hold a relative amount of weight.

Design Process:

In the beginning we did not have any specific goals besides designing and building a bridge with the best cost to weight ratio in the class.  We kept this mindset throughout our time of working on the assignment and never once discussed 2^nd place.  West Point Bridge Designer played a major role in determining a basic design for our bridge; it showed us where an overhead truss bridge experienced tension and compression forces as well as the best way to orient the interior cross members.  During lecture we learned how to analyze a truss which is a way of calculating the exact amount of force each truss member experiences when a given load is placed on the bridge.  This analysis also aided in how we placed the interior cross members.  We did not design individual bridges, instead we came together as a group and designed one bridge.  This eliminated having to pick through multiple designs and allowed us work together as a team.  Our bridge was designed during the construction process due to the use of fixed length K’Nex members as well as gusset connection pieces that limited angles to increments of 45 degrees.  During the open testing time we had in lab, our bridge was able to hold 35 pounds so to be safe we predicted that the bridge would fail at 30 pounds.

Description of Final Bridge:

Our bridge is a 38-inch, three levels high bridge utilizing many triangles throughout the bridge. The members are designed to push the force on the bridge outwards towards the edges of the bridge. There is more strength on the center of the bridge to accommodate for more force on the middle of the bridge. We wanted to add additional levels on the bridge because we figured that one tier would leave the bridge too weak in the middle, especially as more weight was added onto the bridge. You can see a hand drawn sketch and a photograph of the bridge (as well as the final cost of the bridge and the number of pieces in the bridge) below.

Figure 1: Plan/Elevation Drawing

Figure 2: Bridge Picture During Testing

Figure 3: Bridge Cost and Materials

Testing Results/Conclusions About Bridge Design:

For the most part, our bridge design was successful. We made a very accurate prediction as to how much weight the bridge held. Based on our design and previous test runs, we predicted the bridge to hold a total of 30 lbs. We also made this assumption based on our truss analysis we composed a few weeks ago. Once the bridge was tested in the final competition, the bridge was found out to have held a total of 29.8 lbs. We think that having only a 0.2 lb. difference was a very accurate assumption.  Even though the bridge held almost the exact guessed weight, we still were partially incorrect in terms of the failure mode. In the precious bridge designs and the one tested in the competition, we predicted the bridge to fail by the joints on the bottom of the bridge being disconnected from the members, usually towards, but not quite at, the ends of the bridge. Now, the bridge did indeed fail by this method. But, this wasn’t the only factor in the failure of the bridge. We took a video of the competition, revealing how our bridge might have failed in case we missed it. We played the video back in slow motion. We then found out that a major factor in the failure in our bridge was that the bridge started to contort and twist, meaning one side twisted clockwise and the other side twisted counter-clockwise. The point in which these two opposites met was not in the middle, but slightly offset from the middle. So, we were right in every aspect in terms of load and failure mode except the one aspect of the failure mode where the bridge started to contort. You can see a video of the bridge failing below.

Bridge Failure Video

Future Works:

Every group was going to fail at some point; and every group, including ourselves, could make some changes to improve the bridge either with weight or the cost to strength ratio. We feel that we could to two things to our bridge that would put the design to its full potential. We also would have stuck with the same/similar design if we were to create another version. We felt that the design we had had an adequate cost to strength ratio. The first change that we would make would be to add various pieces to the bridge to help with the tension problem, specifically at the bottom. Throughout this term, the main problem we have been facing was the tension along the bottom. If we were to decrease the rate of failure due to tension at the bottom of the bridge, the next main mode of failure would be contortion and twisting of the bridge. The easiest and most effective way to fixing this problem would be to add lateral cross members to the bridge. This would give strength to the bridge so that contortion would be much more difficult. Even though these two modifications would be a little costly, they would in turn cause the bridge to hold much more weight. Ultimately, these modifications should help improve the cost to strength ratio.