Term Review

Experiencing the design of large bridges was a very interesting process to follow for the Spring Term; especially for student engineers with few experience in industrial related creative-release-opportunities such as the project for past module.  While designing large bridges, the entire class learned about angles, pressure, and the possible structural benefits as well as possible disadvantages.  I personally became very involved in how the pressure from the superior force pressed by motion and weight was distributed differently through out the parts of the respective bridge structures and the different designated joints and pieces, bridge sections, and their evolution through out their improvement upon changes chosen by the group members.  Hopefully it all serves me more towards the future and its upcoming engineering opportunities.

- Ana M. Franco

Term Review

This term has been full of new experiences and has taught me a lot.  I had never before realized what it was that real engineers do in the real world.  I can also honestly say that the goals posted for this term were met and I have learned something about each of them.  This was a team project so teamwork was an integral part of being successful and getting along as a group.  Planning and documenting were needed when we had to design our own bridges, plan what worked best, and then document our final results with each test.  Modeling was a huge part of this quarter.  We modeled on computer programs and using physical pieces to model our ideas.  I learned new computer programs that I had never even before heard of and it has been years since I have played with K’nex.  Finally, we used analytical methods to determine the weaknesses of our bridge designs and to help us improve our designs.  

I really liked how this class was run.   However, it was not connected to the Engineering 103 lectures that we had to attend every week.  Instead of changing the course to fit the lecture and layout of every other class, I think the engineering lectures should be more generalized.  Maybe they could talk about companies in the area or what employers are looking for or something else besides the syllabus for the rest of the Engineering 103 labs.  I felt that this class should not be changed.  We didn’t need to write a design proposal or do half of what the other labs did, but I felt that it was an appropriate level of work for this class.  I also liked how we were responsible for our own blog posts each week.  I have been in groups where people don’t always pull their own weight and it is nice that my work is reflected in my grade, and no one else is riding off of the work I am doing.  It is a big change from Engineering 101 and 102 and I really welcomed the chance to do the work for me and only me.  I also really appreciated the fact that we did not have to do presentations during week 10.  I felt that since everyone was doing the same thing, it would have been really redundant.  Also, without having to prepare for a presentation, we could focus more on our designs and documenting our results.  The only thing I think I would change if doing this module next year is to have some more to do during class time.  A lot of the time my group would be done early in class and we wouldn’t know what else to do until we were dismissed.  Also, at some points we needed more K’nex pieces.  Otherwise, I would absolutely advise any incoming Engineering 103 student to take this class. 

Last week in lab we finally got to test our final design of our bridge.  We were really excited because we made a lot of changes to it and really thought it was going to do well.  However, we weren’t all that surprised when it failed relatively early.  We knew our bridge was going to fail from twisting, and it did so after only adding 14.7 pounds of sand.  This is a low number compared to most other groups, but we know that we did the best we could and we tried our hardest.  However, I am happy that there was at least one group who had a worse cost to load ratio; it makes me feel a little bit better about our efforts.

Term Review

Last week in class, our group tested our 3' bridge design. Before doing so, we'd submitted a survey about the bridge to our professor who put the info provided by the survey into an Excel sheet. Using the Excel sheet, the entire class was able to compare the cost and strength of each bridge, side-by-side. As a class, we decided to test the bridges in order of highest to lowest predicted cost-to-strength ratio. Which group went first? None other than ours. Even worse than the 17 pounds we'd predicted our bridge would hold, it only supported 14.7 pounds in the final test. To make things worse, this meant our cost-to-strength ratio was even  greater than we'd estimated.

Now that the final competition is over, I can look back at all the steps we'd taken throughout the course and honestly say that I learned something worthwhile about every single one of the topics identified in the goals for the course. Working with a group required teamwork. Planning, documenting, computer modeling and physical modeling were all part of the design process which our group followed throughout the course. We used some computer software I'd never used before, and we used some computer software that I've already been familiar with for years. Lastly, we used static and forensic analytical methods to learn more about the weaknesses of our bridge designs.

I think the only thing that was not beneficial to me was the fact that this Engineering 103 lab was disconnected from the Engineering 103 lecture section of the overall course. If the bridge lab could be formatted to follow the general pattern of the assignments for all the other labs, I think I would feel like the Engineering 103 lecture section of the course was more important to me, since it is something I am required to attend. Basically, I just felt that attending the lecture session wasn't very important because I was told to ignore what they told everyone about assignments being due and ways to earn extra credit. On the other hand, I feel that having individual blog posts benefitted me alot. I think this is something that every lab should have. Although teamwork is important--especially as engineers--we are not paid to do the work for our classes, which means some students simply do not care as much as other students. Some students know that other students will do the work for them so that their own grade is not negatively affected by the actions of a lazy student. I've experienced this in Engineering 101 and 102, and the students who did not do all of their work did not have anything held against them. In the real world, they could potential be fired from their job, but in class, they won't even receive an F because someone else will end up doing the group assignment this student was responsible for. Instead, individual assignments reflect the work of each student, even if the assignments show similar results because of two or three students being in a group together.

- Melissa Wetzel

Bridge Process

Now that the term is almost over, I can take the time to reflect on what I have learned.  Before I had taken this class, I didn’t even know what a truss was, let alone that it was a type of bridge.  I was new to this whole topic and was forced to learn a lot in order to succeed in this class.  I thought it was really interesting that bridge designing was such an intense process.  It really has a lot of little details that need to be perfected in order to have a successful bridge.  I had no idea that so much happened behind the scenes during the planning stages of a bridge.  It really is a complicated process.  You need to consider what type of materials to use, how big/long the bridge will be, what type of gusset plates to use, the angles of the trusses, the thickness of each member.  The list goes on and on.  I am just so amazed that all of this goes on.  It has really opened my eyes up to what engineers have to do when designing a real life project. 

Last week in class my group tested our three foot design.  Unfortunately, we weren’t doing very well.  We changed our design a few times and added a lot of gusset plates and more members.  We knew we were raising the cost of our bridge, but it didn’t hold a lot of weight at all.  Our bridge kept failing due to the twisting of the members at the joints.  We tried putting in cross sections in the middle of the bridge to reduce this twisting, but we didn’t get to test it again so we weren’t sure how it was going to work. We hope that this has made our bridge stronger, especially since it is now more expensive.  Next week we hope our prediction of a low weight is wrong.  

Bridge Process

During class last week, my group and I tested a three-foot bridge we'd designed over the course of the previous week. This bridge held only 14.2 pounds and its point of failure was caused by weak joints for the cross beams. Under 14.2 pounds, the bridge twisted and its members popped apart. To fix this, we replaced the weak connections with stronger ones. The original connections consisted of a Knex chord laying in the gusset plate joint. These connections were weak because the chords could slide freely through the plates, although being held against them. The new connections were created with two grooved 360-degree gusset plates joining the chords' ends like two puzzle pieces interlocking. This type of connection does not allow for movement and helps minimize the bridge's horizontal displacement. Next week we will test out three-foot bridge and compare our results to the rest of the groups' results to see which group has the best overall bridge.


Now that my group and I have almost completed the bridge design process for the term, I am realizing how much I have learned, specifically about bridge design. In class yesterday, Dr. Mitchell put three rough bridge analyses on the board. All were the same width and comprised of three triangles in the same order, however each was a different height. According to the analyses, a bridge whose height is the taller, or whose triangles are the least obtuse, will have the least amount of compression and tension on its members under a given load. Another important key to designing bridges that I've learned is that joints tend to be the weak spots. Before taking this class, I always thought that chords were the "weakest links" in bridges, but it is truly the "links" which are weaker. In testing the Knex, I have read information about which joints can handle the greatest stress force before failing, but we have never analyzed the force it would take to snap a chord in half. This is because of weak joints.

Analysis Process

               When analyzing a bridge that an engineer is designing, many factors play a role that you need to take into consideration.  Bridge Designer is great when you are playing around with K’nex pieces or if you want a general idea of the compression and tension forces, but it would not work for a real bridge.  Bridge Designer does not take into effect the load of the bridge itself, the weather, or any other outside forces acting upon a bridge.  I personally would not trust a bridge that was more carefully thought out and experimented/analyzed on.  I also think you need to apply more than a few trig and physics equations to a bridge design in order to make sure it will be a safe, efficient bridge.  

 

                For our class, I would like to take a look at the gusset plates that we are using.  It is hard to figure out which ones are strongest when you can only test your bridge once in class.  I also wish there were general guidelines to using K’nex pieces, such as ‘the longer the members, the stronger the bridge’ and so forth.  I have no idea whether that is actually true or not, and again, there is not a lot of time for experimentation.  Some choices you can make are common sense, but for someone who is new to bridge designing, there is an awful lot to learn.  I also think it would be helpful to have a way to analyze the differences between a two foot bridge and a three foot bridge.  We are not exactly sure that what we did for our two foot bridge will be efficient when lengthening our bridge.  There are just a lot of unanswered questions. 

                Last week in lab Melissa and I worked with Bridge Designer and tried to calculate the forces on our K’nex bridge three foot design.  However, we could not get this to work because “members+3 did not equal 2*nodes”.  This proved difficult to fix since our bridge was centered about a single node, not a member.  It was frustrating to tamper with the design on the computer and find something that would work out similarly.  In the end, the design is simplified in my A3 post because I was really running out of designs to try that still resembled our bridge.  This week in lab I hope to continue learning about the design process and come up with ways to improve the design we already have. 

A3-O'Callaghan

Free Body Diagram:

Calculations:

Finished Diagram with Forces:

Bridge Designer Analysis of Given Truss:

          Based on the numbers I got through my calculations and then the numbers Bridge Designer gave me, I can honestly say I am a little confused.  My numbers are very similar but not exact, which tells me that I don’t have a different ratio, especially because my top member piece also has a compression of 15 pounds.  My guess is that they used the angle of 60 degrees in Bridge Designer whereas as I used 53.13 degrees and that is why our numbers are slightly different.  I thought I would have to use a scaling technique and match up the ratios, but it has not turned out that way.  

Bridge Designer of Our Bridge:

          Bridge Designer would not let us replicate our actual bridge.  Our bridge does not follow the rule: members +3 =2* nodes.  In order to be able to resemble our bridge somewhat, I made the bridge shorter and it is missing two important members than run vertically on the left sides of the two center squares.  In doing this, I’m not sure how much is different compared to our actual K’nex bridge.  I also don’t know now that these ratios will be correct if we apply them to our own bridge.  I am hoping that these numbers actually somewhat depict how our bridge behaves or else it will not be very helpful.   However, this is a twenty pound load, and if I used the same method that I used for the other bridge, these forces would be pretty accurate.  All of these members are connected in 45 degree angles and I feel like Bridge Designer has an accurate display of what the forces would be on our K’nex bridge if it looked exactly like this.  

         This type of analysis could be helpful when building our K’nex bridge.  I might think about following the rule of member pieces to nodes that Bridge Designer requires.  Also, using the testing information about K’nex joints, I have decided that I definitely want to use as many pieces as possible in a single connector.  It has the highest pull out load and this could potentially increase our cost to load ratio significantly.   This also makes me think that we don’t want to use nodes that have a lot of spots for members to attach to them.  If we did put members everywhere they can attach, our bridge would become extremely expensive.