A3-Watson

1.

2.

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

3.

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.

5.

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.