A3 - Kyle Hayes

Ends

   ΣF_X = 0:   F_AX = 0

   ΣF_Y = 0:   -10lbs x 1ft + F_EY x 2ft = 0

F_EY = 10/2 = 5lbs

F_EY = 5lbs

F_AY = -10lbs + F_EY = 0:   F_AY = 5lbs

F_AY = 5lbs

Joint A

   ΣF_Y = 0:   T_AB sin(45) + F_AY = 0:   T_AB = -5/sin(45) = -7.07lbs

                T_AB = -7.07lbs

   ΣF_X = 0:   T_AB cos(45) + T_AC = 0:   T_AC = 7.07 cos(45) = 5lbs

                T_AC = 5lbs

Joint B

   ΣF_Y = 0:   -T_AB sin(45) + T_BC sin(45) = 0:   T_BC = -T_AB sin(45) / sin(45) = 7.07lbs

                T_BC = 7.07lbs

   ΣF_X = 0:   -T_AB cos(45) + T_BC cos(45) + T_BD = 0:   T_BD = -7.07 cos(45) - 7.07 cos(45) = -10lbs

                T_BD = -10lbs

Joint C

   ΣF_X = 0:   T_BC sin(45) + T_CD sin(45) -10lbs = 0:   T_CD = [10 – 7.07 sin(45)] / sin(45) = 7.07lbs

                T_CD = 7.07lbs

   ΣF_Y = 0:   -T_AC – T_BC cos(45) + T_CD cos(45) + T_CE = 0:   T_CE = 5 – 7.07 cos(45) – 7.07 cos(45) = -5lbs

                T_CE = -5lbs

Joint D

  ΣF_Y = 0:    -T_CD sin(45) – T_DE sin(45) = 0:   T_DE = -7.07 sin(45) / sin(45) = -7.07lbs

                T_DE = -7.07lbs

 

Joint E

   All tensions around joint E are already solved for.

My Analysis Diagram

Bridge Designer Analysis



To make sure the hand analysis corresponds to the Bridge Designer, the lengths of the members and the angles must scale to each other. So that all angle are the same between the hand and Bridge Designer analysis. For the members it is just important the relative size to one another is kept the same. If two pieces are the same length as each other than those two corresponding pieces on the Bridge Designer must be the same length. If one is twice the size of the other, than the corresponding piece on the Bridge Designer must be twice the size of the other.



K'NEX

Bridge Designer Analysis

The K’NEX joint test page showed that the pull out for required to remove a member from a joint increase with the more members attached to that joint, it also increase more if it is symmetrical. This test tells us that the average max limit of tension of a member can be 37lbs before the connecter is almost guaranteed to fail, useful information as any member nearing this tension amount must be adjusted and will most likely fail first. We can use the fact the more members per connector increases the tension required to remove the member to strengthen our connection. Where ever there is a spot nearing this maximum tension amount we can add a member that will have a vector force in the same direction as the member nearing the max tension to increase capacity. To explain a bit more clearly, the example only had three of the five slots of the connector use, the other to slots, the ones on the end would not contribute to increasing the strength though as they were only in the x direction and thus can only hold and x direction vector force, but the three that were used either only had a y vector or had a component of them that was in the y direction. This is why adding members increases the tension needed to pull it out, because it is not just that member being pulled in the y direction but some of the pull is being sent to the other member whose vector is in both the x and direction.

    - Kyle Hayes

Week 8- Kyle Hayes

Last week we practiced how to calculate the force on each member of the truss using method of joints by calculating it for a low load simple 7 member bridge. After doing the calculations and following the video tutorial we verified it using Bridge Designer online, and then we used Bridge Designer on our K’NEX design to help analyze the tension and compression of each member which will be used to improve our design as we near the final weeks.

I feel that this method is good for calculation basic tension, but must less reliable when there are many loads that are always moving and changing value rather than fixed to just one joint. Also like many of the other method we used this only calculates for perfect conditions, no live load, no wind or other force, and the members and gussets are perfect fit and perfect condition. So yes, it is a useful tool but not sufficient enough and reliable enough to count for a real bridge.

The one other thing I would like to analyze is the tension of the gussets. What is the max strength of the member-gusset connection, and the strength limit of the two grooved gussets stuck together as they seem much weaker and tend to fail more often than the member-gusset connection in my experience.

This week in class we will be using the data collected from Bridge Designer for our K’NEX bridge and fix our design based on adjusting high and low tension points of our design.

Week 7 - Yilei Jiang

       Last week, we finally tested our bridge and it loaded 34-pounds of sand. At first, the bridge wasn't long enough to fit in a two foot long span. Therefore, we decided to add an extra 2.125" long chord on the base. By doing this, the bridge became symmetrical.
       The bridge started to twist when we added weights because of the structure of our bridge design. We added an extra 5' long chord on the top truss to make the bridge more stable. However, the 5" long chord was beyond the width of the bridge, so it didn't fit too well with the gussets. When we added the load, the bridge started to twist lightly. There were two groove gusset plates in the middle which pulled apart, at first. Then two members from the support points could not hold the load any more, so the bridge collapsed. We planned to fix these problems on our next three-foot bridge design.
        For K'NEX numbers, I would like to know the accurate tension of every piece truss members during the bridge loading. That would help me to design a more serviceable bridge by calculating some trigonometry functions with those databases.
       Next week, we will start designing the three-foot long bridge on the basis of previous designs.

- Yilei Jiang

Week 7 - Kyle Hayes

Last week we tested our two foot span design, our design was two feet long but the span was just shorted so we were forces to add a bit to the length, but over all I don’t think that changed much of the design or the strength. Our bridge’s cross sections were mot all fixed positions so when the weight was added the non-fixed parts were bowing and moving and it caused the bridge to twist sideways and fail because more the sides leaning too much.

For the K’NEX the numbers I would like to know are the amount of force on the bars as the weight is loaded from the middle, as this would help determine the strength limits of that piece and where can be improved and where can be reduced.  My idea for calculating them is to use trig to see how the forces get spread based on its angle but I know that it is more complex than just that.

This week for class we will be using our two foot span bridge and the information we gained from the test to make a three foot span design.

-          Kyle Hayes

week7-xue bai

Last week in class, we fix our bridge, which we were done during weekend. we redesign some part of the bridge to make it stronger. Fist time we want to test the bridge the bridge was too short. We made a bridge that just about 20 inches, and it is not long enough to put on the holder. So we add up our bridge and test it. It comes out to be good. The problem we do not think about is, out bridge twist to one side. That cost our bridge to fall. Next week we would work on our 30 inches bridge. The 30 inches bridge was harder that the one we made now, but I think we could do it.

When we use the west point bridge design, we get the data of which part is easy to fall apart. How many tension and compression it holds and how many present was been used. It really help to find out what parts hold the most force. Which parts need to be stronger and which part could use fewer pieces. If we knows that data, we would make a more effect bridge. The other data may also could be helpful would be how much the bridge can hold. In the time when we build the bridge we could only made it a strong as possible, but we do not know if one piece of our bridge is remove is that cost the bridge any different. This data we may could get from the test data.     

Week 6 - Yilei Jiang

         This week, we built our own design K'nex bridge to see which one was the best one and the good components of the designs.  We decided to build a design which without bottom truss. Besides, it was also the design which had the lowest budget. After we done, I found one thing during the testing that the weakest part of this bridge was those grooved gusset plates. They were always pulled apart when we was adding the weight. Especially, the gussets from two piers of the bridge were so easy to separate.  I thought that the reason was  the bridge had one-side truss. So I suggested to build the bridge with top and bottom truss. However, the testing result was same. Our second design only could hold 20 pounds before it was fallen to pieces. Then we started to think about the reason. And I felt that we could shorten the height of the bridge because it can support well. Our original base was the structure like this" |\|\|\/|/|/|". And now if we change 5"long chords to 1.25" long chords, the bridge's structure will like " |\/|><|/\| ", which I think can be more stable. The other idea is that we decide to use more groove-less gussets to avoid using grooved gussets. That can not reduce the cost but make the bridge into pieces easily.
      
        For the next week, After working with Knex for a week reread we entry of last week and state how our views of the similarities and differences have changed. Then we will test our design on a 20' span. And we will fill out the bridge results recording before we leave the class.         

week6-xue bai

This week in class we start design our first bridge by K’nex. We first try the single structure and it end up becoming too weak and cannot support a lot of weight. Next we try the triple structure. The structure is strong in the middle and weak at two sides. By the end of the class we still work on the bridge. Next week is the first we load our bridge. We would try to get the most weight by the lowest cost.

The K’nex is mostly what I think in the last week. The K’nex do not have enough type of piece to whatever shape you want. The design is really limited. The piece have the same size, it also made the design become limited. If I get the chance to design a real bridge it would be different in many different way. The fist is the cost of the worker would be a new cost of the bridge, which is, not be part of K’nex Bridge. The second one would be the nature. The rain, wind, even sunshine can cost a different effect on the bridge. There also would be so percentage errors that happen on building or design. Make a really bridge is much harder than the K’nex bridge.