Week 10

Last week in class we got to test or final bridge design.  The testing went in order of predicted lowest cost to weight load ratio.  The strongest bridge in the class could hold about 102 pounds and cost around $800,000, but was still able to have the best cost to weight ratio.  Our group was disappointed in the way our bridge performed.  The bridge held about 31 pounds and cost around $380,000.  We were disappointed because in the previous the bridge held around 41 pounds and we had not modified anything.  After the testing was done everyone submitted how much his or her bridge had held.  It’s too bad this was the last time we got to play around with the bridge because I really enjoyed this lab.

            I couldn’t be any happier with the way this lab worked out.  I definitely like this design lab better than the previous two.  I feel like all of the topics were covered well.  This lab really made me learn to document everything because in the blog you would have to write about what happened.  Teamwork was also something that was really emphasized.  I felt like our group worked very well with each other.  The thing that was least beneficial was the truss analysis.  While it did teach how the to calculate forces on members there was no way to really apply it to your own bridge.  I think the quality of the fellows was the most beneficial.  They were much more helpful than the fellows from the last two terms.  They actually wanted to be there and wanted to help in any way possible.  I don’t really have any suggestions for next time.  This course was organized very well and a lot was learned.

Week 9 Post

In lab last week our group worked on our 3 foot bridge. Compared to our 2 foot bridge we had drastically changed the outlook of the entire bridge so we could cut down on the bridges cost which was our main issue in the last competition. For this bridge we also had to have a 2" by 3" passageway so cars and trucks could have space to cross our bridge. When we first came across this challenge it seemed to pose a problem but after some tweaking and playing with certain ideas we came to our basic design. One of the main goals we wanted to do for this bridge was to remove any grooved gusset plate that we had and find a way to replace them without getting too far away from our original design. When we removed the grooved gusset plates it immediately made a huge impact on the total cost of our bridge and it gave us some extra money to make other adjustments to improve the strength of our bridge. When we tested our 3 foot bridge it was able to support 42.3 lbs. which we were a bit shocked at proud of at the same time. Seeing as both out 2 foot and 3 foot bridges cost about the same and our 3 foot bridge held more weight than our 2 foot bridge we knew we were on the right track and have a chance to have the most cost effective bridge design. We hope to do well in the competition and maybe get atop the board and get some extra credit.
This term is almost and when I think about what I have learned in this course. I did not know a ton about how bridges actually functioned and how, but after this course I have a better understanding of them. I learned a lot about why truss bridges are a very commonly used bridge structure and how they are able to disperse weight on their members to hold the tremendous amount of weight that gets put on the each and every day. Also, I learned that the bridges we see out in the world are not there because someone just decides to come up with a plan for a bridge that would be the best bridge ever, but you have to take time and design a bridge that has a good amount of strength to it and is cost effective to build. Especially for our competitions, the cost-to-weight ratio was how we determined the effectiveness of our bridges by comparing the bridge's overall cost to the maximum amount of weight it can support. Weight distribution is a very important skill that was also taught to us in class. We used set of calculations to determine how the force, either tension or compression, would be dispersed throughout that entire structure. This class was definitely a good class to have because the thing I have learned and the skill set that I now have for being in this class will help me in my future endeavors.

-Robert LaChance

Week 9 Blog Post

Last week in lab, we made some major changes to our three-foot bridge design. We made these changes primarily to cut down on the bridge's overall cost. Another reason we implemented such major changes is to compensate for the additional constraint of a 2''x3'' rectangular space through the bridge. This constraint was added to simulate the construction of an actual bridge, allowing an area for vehicles to travel over. The biggest difference between our original bridge and the new bridge is the removal of all grooved gusset plates. We removed these pieces to significantly cut down on cost, being that the grooved plates were twice the price of standard gusset plates. After testing our new, three-foot bridge, we found that it was able to support 42.3 lbs. This was an incredible improvement being that our three foot bridge was able to hold more weight than our two foot bridge at almost the same cost. Needless to say, we will use the newest design for the competition.
The term is almost complete. Looking back, I learned a great deal about bridges, bridge design and bridge testing. I learned the most about truss bridges. I now know why truss bridges are so commonly used. They are able to support the most amount of weight due to their design. I also learned that you cannot simply judge a bridge's effectiveness by how much weight it can support, but you must also take into account the cost of the bridge. The cost-to-weight ratio is possibly the most efficient way to measure a bridge's effectiveness by comparing the bridge's overall cost to the maximum amount of weight it can support. Another important thing I learned was how to calculate weight distribution. Weight distribution is a very important set of calculations to perform when designing a bridge. These calculations will be able to determine how and where a bridge distributes weight in the form of tension and compression. The things I learned in this class will stay with me throughout my career as an engineer and I'm very thankful I had the opportunity to work with bridges.

Week 9

During last week in lab we got to work on our three-foot bridge design some more.  This was the last week we had to work on our design before the competition.  We built our bridge from scratch again.  Some things we kept in mind while making the bridge was to have a 2”X”3 hole through the middle.  Our first design looked like a square prism with trusses that looked like X’s on the side.  One thing that we did change from last time was the trusses on the inside of the bridge, which would prevent it from twisting.  When we tested the bridge it failed at around 24 pounds.  When we went back to the table we added some minor pieces that we thought would give the bridge more strength.  This ended up doing nothing.  In our final design we put a top truss on the square prism.  This design yielded about 40 pounds.  This was a success in our eyes so this is the design we will submit for the competition. 

            I came into this class with zero knowledge of bridges and came out knowing a ton more.  One thing that I noticed is different about me is that whenever I come across a bridge now I analyze and look at how it is built.  Trusses are one of the most important aspects of bridge design.  We learned how they distribute weight and make bridges that much stronger.  They have been around for about 100 years.  While designing the bridge you really learn how everything affects everything.  The best bridges are not just the ones that can hold the most weight or cost the least, but the ones that have the best cost to weight ratio.  One of the best technical things I learned how to do was figuring out compression and tension by doing physics/calculus.  When building a bridge there are many factors you have to account for including weather and aging.  The list of things that I learned can go on and on but these are just a few.

-John Watson

A3-Tillman

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4. By comparing the "Bridge Designer" sketch with the hand-written results, one will notice that the results do not match up. The reason for this is because the "Bridge Designer" program does not work in units. Scaling both results will use the same units for each method of calculation, resulting in equal final answers. 

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6. Using this type of analysis is a great way to visualize the weight distribution of our bridge. After seeing on our bridge where exactly weight and tension are highest, we may choose to strengthen these areas by using more Knex pieces or slightly rearranging the joints to decrease the chance of the bridge breaking at that point. Also, some pieces seem to not be managing any weight or tension at all. We will most likely remove these pieces to cut down on the bridge's overall cost. 

A3-Watson

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Joints	Tension(N)	Compression(N)
AB	0	51.36
AC	25.68	0
BD	0	51.36
BC	51.36	0
CD	51.36	0
CE	25.68	0
DE	0	51.36

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4. From the pictures above you can see that my calculations and the Bridge Designer screen cap do not match up.  This is because in Bridge Designer there are no units.  To counter this the hand written calculations have to be scaled.

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6. From using Bridge Designer you can really tell where all the tension and compression are.  From the analysis from the link you can see that adding more K'nex to the joint, making smaller triangles, makes it  harder to break the joint.  We may add smaller triangles where the tension and compression are the greatest and maybe take K'nex out of joints that have small forces acting upon them.

Week 8 Blog Post

Last week in lab, we were taught how to calculate forces acting on a bridge by hand. Such forces include compression and tension. We do this by applying trigonometry and physics to a two-dimensional sketch of the bridge design. These calculations are very similar to those carried out by the West Point Bridge Designer computer program.
While these calculations provide accurate results, they would not be as effective on an actual, full-size bridge. When calculating forces on a real, physical bridge, one cannot assume that weight is the only force acting on the bridge. Outside forces such as weather and extreme heat and cold can affect how the bridge distributes compression and tension forces.
If given the opportunity, I would be interested in calculating how environmental factors affect a bridge's ability to distribute weight. To do this, I would have to add an X and Z axis to the sketch and calculate forces on those axes as well.
This week in lab we will take another look at our bridge after analyzing the results of our calculations. Depending on the outcome, we may decide to slightly alter our bridge's design. I'm excited to see how accurate our calculations are at determining where our bridge will most likely collapse.

Week 8- Post

In last week’s lab we were taught how to calculate the forces on a bridge by hand.  We were taught about Bridge Designer in the beginning of class and then split up into our groups to do the calculations of the assigned bridges.  Westpoint Bridge Design has some definite similarities to the Bridge Designer, both programs calculate compression and tension and both programs only view the bridge design from a 2-D perspective rather than a 3-D perspective. In lab we also went over free body diagrams and the calculations behind them.
            For a real bridge we would have to take into account of other forces would have to have other equations to use for the members connected both sides of the bridges. To calculate to forces being dispersed through the top, bottom, and the other sides of the bridge we would need more equations to do so.  Weather like wind, snow, rain and wear from cars and ageing would also need to be taken into account.  In the end it may never be possible to know exact how long the lifespan of a bridge may be or how the condition will exactly be over extended periods of time, but some programs can get close.

Week 8 Post

In last weeks lab we learned how to do calculations of bridges by hands.  We first had a group discussion where we learned about Bridge Designer.  This program reminded me of Westpoint Bridge Design in the way that you make the bridge on only side and the program also calculates compression and tension.  We then went over free body diagrams and other calculations.  After we split off into smaller groups we had the chance to do calculations of a given bridge by hand.

            This analysis would not be sufficient for a real bridge.  For a real bridge other forces would have to be put into the equations also there would have to more known about the members and joints.  These calculations were also for only one side of the bridge.  We would need to analyze the top, bottom, and the other sides of the bridge.  Other things would need to be accounted for like weather and wear and tare.  It would also be nice to know how much the bridge could hold and an estimate on it life span.

-John Watson

Week 7 Blog Post

     Last week during lab each group got to test the 2 foot bridge each group made. After a miscommunication about who was supposed to bring the bridge to class we were able to make minor tweaks to try and get the bridge cost down while making the strength of the bridge increase. We also had to make the bridge slightly longer because we made the bridge exactly 2 feet long and it wouldn’t sit on the supports that were used for the test. Furthermore the cost of our bridge was through the roof and we need to change the outlook we have when building the 3 foot long bridge. The total cost was somewhere around $375,000 which was far more than any other bridge, but our bridge did hold 39.4 lbs. which we all believe was an amazing feat. For when we are building the 3 foot bridge I think that we should lower the cost by not using grooved gusset plates which, when tallying up the total amount, were the biggest contributors to the cost.
     For lab if I could see some of the forces that West Point Bridge Design shows you I would really want to see where the tension is specifically on the gusset plates. The reasoning behind this is that when every bridge in lab broke it was at a point where a gusset plate had a connection. I personally do not believe that compression would be necessary to see because the Knex pieces are pretty strong and the only weak part that I see is at the point of connection with the gusset plate. I would like to be able to test our 3 foot bridge more in lab before actually putting back into the competition so that we can get a better feel of what exactly is going wrong with our bridge so we can fix it and try again rather than just thinking in theory about how we could possibly make our bridge better. Or goal for next lab is to definitely get our cost to weight ratio down so we have a better chance of being the best bring next time.

-Robert LaChance

Week 7 Blog Post

Last week in lab, we were able to officially test our bridge and make any desired changes. After making a few last minute changes to the bridge to cut down on cost and make the bridge slightly longer, we tested the amount of weight our bridge was able to support. We tested this by placing the bridge between two sawhorses and hanging a bucket from the center of the bridge. Sand was then slowly and continuously added to the bucket to add weight. The maximum weight our bridge was able to support was 39.4 lbs. I'm very happy with this result but I would like to significantly cut down on cost to bring down our cost to weight ratio.
As I mentioned earlier, one of the biggest differences between West Point Bridge Designer and Knex testing is that the Knex bridge construction does not provide us with exact calculations of weight and tension like WPBD does. When testing with Knex, I would like to know the exact areas of our bridge where weight and tension are highest. Knowing this would help us make necessary adjustments to the bridge to further increase the amount of weight it can hold. Calculating these on the Knex bridge would be very difficult. However, I was able to determine where the bridge gave out when it reached it's weight limit and collapsed. I recorded our test trial and by viewing the video in slow motion, it is clear to see that the bridge gave out on the left side, right where the lower support truss section ends. In order to correct this, we could add more supports in that area but at this point we are focusing mainly on lowering cost and removing unnecessary pieces instead of increasing strength. We have some ideas on how to lower cost and I look forward to continuing the testing in lab this week.

Week 7

Last week in lab we got to test our bridge design.  The bridge we tested was 2 feet long.  The bridge had an under truss, which when tested the bridge broke where the under truss ended.  The reason we put the under truss in was so that it dispersed the weight.  When tested our bridge held about 39 pounds.  The problem was that the bridge was way too expensive.  I think our bridge ended up being the most expensive in the class, which was about $380,000. The amount of joints used is what gave the bridge most of its cost.  To combat this we decided that we have to make our members longer so that we used fewer pieces therefore making the bridge less expensive.  Since the weakest points on the bridge is the gusset plates we will have to come up with a solution to make them stronger some how.

            As far as numbers go I would like to see where the most compression and tension is on the bridge.  This is so we can see where to add more supports and even take pieces off if they do not add any support.  This would also be great to see if other designs work better.  The only way I can think to test of compression or tension is to feel for it.  You will have to try and bend members with your hands and see which ones resist the most.  Unfortunately you cannot see all calculations in real life like you can in Westpoint Bridge Design.

Week 6 Blog Post

In week 5 our group we started to form our 2' Knex bridge. When forming the bridge we took ideas from each persons bridge in hopes that it would create a great bridge. We had to make some comprimises because when we came up with ideas for the bridges they could only really work in West Point Bridge Design. When we first made the bridge we used my design and just used some tight cubes to span the required length. Later in the class we added another layer on top to add to the strength of the structure and unfortunately the cost of the bridge. The total cost came out to around $250,000 which can and will be improved on.

In relation to how I viewed the differences last week between West Point Bridge Design and using the Knexs stands. Knex have a limited amount of materials that can not be used to make the more complex angles and be used to opptomized for the bridge to be the least costing posible. While West Point Bridge design has a more unrealistic view to it, but will show you where more supoort or losst support is needed. For the week ahead I would like to keep working out the little things to make our bridge a little bit better at a time. Can not wait to test out our bridge!

-Robert LaChance

Week 6 Blog Post

Over the course of last week, week 5, we worked more with Knex. We put together some great ideas from everyone in the group to create one group bridge. We, as a group, decided to spend a little more money, using a lot of pieces, and attempt to build a bridge that can hold very large amounts of weight. We were able to test the bridge and were very happy with the results. Our bridge was able to hold more weight than could be fit in the testing bucket. In regards to the difference between Knex and WPBD, I stand by my previously stated differences. The biggest differences are still the physical presence of the Knex bridge and the overdramatized bridge movements in WPBD.
There are many differences between working with Knex and building a real steel bridge spanning about twenty feet. The first and most important difference is that in the construction of a Knex bridge, no lives are in danger. With the Knex bridge, a small scale model is created to simply test how much weight the bridge can hold versus the estimated cost of producing the bridge in real life. Another major difference between creating a Knex bridge and a real bridge is that the Knex bridge will not be exposed to weather and other natural effects that factor into a bridge's functionality such as wind, rain and extreme heat. These factors would also wear down a standard bridge over time by means of corrosion.
This week, we plan to do more testing on our bridge and edit it accordingly. We will possibly remove some less important pieces that could save us some money. Depending on the outcome of the tests, we may decide to alter the bridge's design slightly. I would like to do a little more testing of our bridge's ability to distribute weight and make necessary adjustments. My biggest fear is that the bridge will not be able to evenly distribute the weight of the bucket. Regardless, I am excited to continue working on our bridge in lab this week.

Week 6

In week 5 we finally got to start working with Knex.  When making our 2’ bridge we combined all of our ideas together.  We took designs similar to the ones we drew and the ones we created in Westpoint Bridge Design.  Our design was a little bit expensive.  Apparently it only costs $250,000, I think I may cost more but I did not do the estimate.  Our first design started out with a bunch of cubes put together to span 2’.  We tested this design out and there was not enough weight to break it.  After we brought the original bridge back to our station we added a top piece that covered the middle.  This design now looks similar to the one I made in Westpoint Bridge Design but with different trusses. 

            My views of the similarities and differences have not changed at all.  Obviously there are going to be a lot of differences between a Knex bridge and a 20’ real bridge.  The first thing that comes to mind when comparing the two is the materials that are used.  Cement and steel are a lot different then plastic.  The real bridge will be able to hold a larger weight because of the stronger materials that it has.  Another thing is that the Knex really limits what designs you can make.  There are only certain angles that you can make with Knex but on a real bride you can make what ever angle you would like.  In the real world a bridge cannot simply be tested like the Knex to see how much weight it can hold.  Engineers need to be 100% sure that their bridge can hold X weight otherwise lives are being put in danger. 

        -John Watson