Week 9 - Yilei Jiang

       During the last week, we worked on building our three foot span bridge. we didn't change our design a lot because we thought that is the most serviceable way to build. The bridge we had based on the tension and suspension measured by "Method of Joints", also depended on the predicted price. We then tested the bridge using the parameters we will be using in the next week for the official testing of the bridges. It was able to hold decent amount of weight on the first try (about 25 lbs) so we decided to reduce its cost by removing some of the members connecting the two sides of the bridge. We tested it again but the amount of weight it held dropped significantly. So our plan for next week is to re-design the final bridge that can hold decent amount of weight without failing which we will be test during week 9. The only accomplishment this week was to test the same design with different number of members connecting the two sides of the bridge which gave us an idea on how much the connecting pieces contribute to its weight holding capacity.

      We have completed almost 9 weeks of the bridge module which has brought many new things into my perspective. I learned quite a few things from the bridge design tools such as WPBD, Knex, truss analysis etc. that we utilized throughout the term. One of techniques I learned in designing a bridge when our goal is to have the lowest cost is that you can analyze the compression and tension forces using WPBD and try to reach the ratio of 1. This can be done by using different variations throughout the bridge which include changing the member size, material and length etc. while reaching a ‘functioning’ bridge. However, in real world, the bridge would be undergoing a lot of external forces such as wind turbulence etc. The amount of force applied by the vehicles travelling over the bridge would also vary constantly. So to ensure the safety, the bridge would have to be designed such that it can withstand the maximum amount of force. Every members and gusset plates would have to be analyzed in great detail to ensure that they wouldn’t give up under the normally expected force. In this case, the safety would be the first priority, not the overall cost of the bridge.

week9-xue

Last week in class we start work on out 36”inch bridge. The 36”inch bridge has a different rule than then the first one. The 24” inch bridge only have rule on lengths, but the 36” Inch Bridge have limited on high of the bridge. The span of the bridge is also increasing a big amount. That made the second bridge has a lot of different part than the first one. By using the force calculation we find out that the 36” bridge could not be simple as make it longer. It needs a lot of change. We are trying to work the best way thought to make a better bridge. This week in class we are start to text our 36”bridge. The 36” bridge would be a more advance bridge. We have learned a lot of different thing in the class. We also get data from our test information. I am really exciting to see how does our bridge do in the finial competition. I believe this time our bridge would improve.

    This term engineering class I really learn a lot. First I get know different type of the bridge, Especially the truss bridge. We get know about truss bridge, and use it in all our bridge. The first bridge is doing on the west point bridge design. The west point bridge design give an ideally bridge. On the west point bridge design we could test bridge and see the weight that is do on each member. That is very helpful for future design. After the west point bridge design we start our k’net bridge and learn how to calculate the force on each member. How to make a good serviceable bridge in a low cost is our finial goal. In the class we use a lot of thing we use in physic and really life to made the best bridge we can possible make.  

Week 9 - Kyle Hayes

Last week we finished our work on the static of bridge design using the method of joints to solve for the forces in the members. We also worked on finishing up and testing the final design of our bridges, testing numerous small factors and detail to minimize cost and increase strength. Small changes such as changing the length of pieces and changing the gusset type.

What I have learned about bridge designing is that the maximum capacity of the bridge is determined by the maximum pull out force of a gusset and that the tension can be reduced in a member via the force distributing to adjacent members. I learned that the point of failure is at the gussets and usually occurs at the ends as they have to take all the weight to disperse it to the ground. Also I have discovered through testing that having fixed connections are important as free ones cause the bridge to be able to shift and bend and will cause a easy quicker failure. I learned that hollow bars are better to use then solid bars as they have more give and flexibility, and that the most stable shape is the triangle so it is essential to the design of a truss. Finally I learned that the cost of a bridge is directly proportional to the weight of the bridge. There were many other things that I learned but this are some of the most important

This week in class we will be having our in class competition to see what group had the highest strength to cost ratio. All are work and testing comes down to this.

    -   Kyle Hayes

A3 - Yilei

• Free Body Diagram & Calculations

     By using the "Method of Joints", the analysis of the truss bridge is showed below. The bridge has a span of 24", a height of 8" and a load of 15 lb at point C.

• The overall forces can be seen below.

• The  same results of analysis in The Bridge Designer's version. 

       The online Bridge Designer is a program allows to design a virtual truss, and then put a load on it. It will calculate the tensions and compressions of each members itself. 

       When I did this program, I had to use the same scale of all members and angles to correspond the results of my hand analysis.  I made each grid be 2"so that the length should be 12 grids. And the height should be 4 grids. Then I picked up the middle node of the length to put a load on, which was 15 pound in this case. Consequently, I got the most approximating forces equaling the ones calculated by hand.   

• The results of analysis of our two foot span bridge in Bridge Designer program.

        Might because of our design, it was hard to computed via the Bridge Designer program. Our two foot span bridge has a bottom truss. So when I completed the adding process and pressed the calculate button, there's an error came out. It said that we had to followed stable structure is M + 3 = 2*N , where M is the number of members and N is the number of nodes. The simulation will not calculate forces unless this condition is met. Thus, we changed our K'Nex design a lot. Besides, we did looked the K'Nex joint test page and it showed the tension would increase if the bridge is symmetrical. So we did the bridge symmetrically.

        That type analysis of the K'Nex truss bridge can find out the strong and weak parts of the bridge by using the average strength of each joint. So we can change our design to reach the proper number. That can make the bridge more stronger.    

week 8 -Yilei Jiang

       I learnt the "Method of Joints" during last lab which is s a way to find unknown forces in a truss structure. This method also would be used in completion of the A-3 assignment.The method of joints consists of satisfying the equilibrium equations for forces acting on each joint. In the lab, we also discussed some ideas of our next three foot span bridge. We agreed that we would use the new method we learnt to calculate our new design to get the most serviceable design.  


       After the amounts of calculating, I think this method of analysis, the "Method of Joints," is not sufficient for a real bridge for some reasons.  First, a real bridge should be tested and analyzed in many more ways than just testing a downward force on a connection joint. Even this method shows the tension and suspension of every members, a real bridge could not be built of this simple databases. Secondly, A real bridge is not only hold its own weight but also deals with dynamic loads and the things like side pushing from the side and even up drafts from underneath. "Method of Joints" does not show that side.  
    
      I am not saying that the "Method of Joints" is completely useless because it at least shows the force when a truss bridge is under a special circumstance, which is  in equilibrium. If a truss is in equilibrium, then each of its joints must be in equilibrium. That's how this method works. This method is one of many methods that are used to analyze bridges. Of course there should have more different calculation for a real bridge. 
      
      There's one thing I'd like to further analyze, which is the accurate breaking point of the K'Nex gussets when they are   experiencing forces. I think that this information would be useful at our next assignment, which is designing a three foot span bridge.
      
      For next week, we will working on our new bridge and complete the comp2.

week8 - xue bai

Last week in class we start work on the basic calculation of the force that on each member. We learn how to use free body diagram and trigonometry to get the force that is one each member, but it need a lot of calculation. The bridge design is the next thing we learn that could help calculation the force. It was very quick and useful. It is better the calculation by hand. I believe we can do a better job on our second bridge.

Next week we would start to work on our second bridge. By the experience we had on our first bridge and the ability of analyze the tension and compression of each member we can design our second bridge in a better way and made it more effective.

The ability of analyze is very helpful but it also have a lot of limited. Analyze we learn just calculate the force form one side but not all the side. The structure in the middle also can be affecting the finial load. In the first test our bridge is fall down because of the twister. The bridge design did not count the chance of bridge twister. The other part that is also very important is the joins. K’net has a very weak join. It fall apart very easily even the member can support the loads the joins could fall apart and made the bridge fall down. It better to know the limit for the join and how much force is do on it. That could help a lot.  

A3 - XUE

 Free Body Diagram

Angle Calculations

Calculations

Replication of Analysis in Bridge Designer

In order to make sure results of the hand analysis correspond to online Bridge Designer I use every square as a two time two square. The length of the bridge is 36’’. That meant that I use 18 little squares as my base and my high is 10’’. That made my bridge has 5 squares high. So my hand analysis has same angle as the online bridge. Same angle is very important in the calculation. That make sure I have a correct number in my online bridge designer. The online bridge designer also is a tool to make sure my calculation is right. My number of calculation is mostly match to the online one, so my calculation should be right.

We change our bridge a lot to follow the ruler of member add 3 equal twice the nodes. The online Bridge Designer cans only calculation particular member and nodes. That made the calculation it give did not match the number the number we get in the text. But I try my best to get it as close as possible. I put 35 pounds load on the bridge. It should that some member get a lot of forces in other hand some member did not get any of the force. I do not know is that number come out because my changer of the structure or our bridge have this problem in the first time. However get to know force on each member is very helpful in future design. We can improve our design and made it became more effective by that way. Such as cut up the member in the place that have less force or do not have force at all. Add more members to the place, which has a lot of force. In the picture shows that middle has a lot of force. We may add some member in the middle. The online bridge design was very helpful. I hop we can made a better bridge next time. 

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.     

Week 6 - Kyle Hayes

This week we built and tested our individual designs to see what was the best and what were good components of the design. Upon reaching l design and testing it, we found that the ends were the weakest and failed after a few pounds and the grooved gussets were pulled apart easily so to make it stronger at the gusset and cheaper we will use non grooved gussets and to help with support we made the pieces between the gussets shorter. This will make it more stable, compact, and cut cost, but this will require more pieces which will increase the cost a bit but not over the original design.

I feel the same about what I stated last week about WPBD and K’NEX, both are fairly different and the K’NEX is much more restrictive. The difference with Steel and the K’NEX is that the steel would allow for customization of length and gussets and thus give more options it rather than just ten fixed pieces. At the same time give many more options and starts to be a bit like WPBD in that you have price dependent on weight rather than piece and you have to pick solid or hollow and the length and it becomes more complex to figure out the bridges strength.

Next week we will be testing our K’NEX design for the two foot span, followed by going back to improve our design and prepare for the final test with the three foot span.

    - Kyle Hayes

Week 5 - Yilei Jiang

      The lecture I experienced from this week was abundant and useful. I knew four major components of a truss bridge. And I familiarized with my team member how the K'nex from shapes. I basically knew the steps of designing a truss bridge in reality from the K'nex, like making an idea; choosing materials; build as a model;  budgeting; testing; editing and etc. There must have a lot of different in detail when I am doing a real project. And for K'nex, I felt the materials could predetermine how the bridges look like. I didn't feel that when I made a bridge via WPBD. Besides, K'nex is a real and touchable toy and lots of problems will come out. For instance, in WPBD, the truck has such a strong climbing ability. It can still pass the bridge when it is down to the bottom of canyon.  However, it will never happen in reality. So when I test the K'nex bridge, it will collapse if it can hold the weight any more.
       I also listened a speech in class. It was a speech by Mr. Jay Bhatt, our engineering research librarian, about the most efficient way to look for engineering-related books from Drexel Libraries. He demonstrated the way that searches different resources in the class. I felt that that made my study much easier than before.
       For next week, we are processing the K'nex. We will pick the best idea from our  team and build it with K'nex.
     
   

A2 - Jiang

     The idea of my bridge's shape is from the results of West Point Bridge Design I tried last week. During several times of experimentations, I found that it was much easier to make a bridge for doing bottom and top truss at a same bridge. I tried to do only bottom truss, like Deck Truss. However, the bridge always collapsed when the truck was passing. And the bridge even cost me more money when I finally made it without top truss because I have to add more web members to make the bridge be stable.  My original design, which has both of bottom and top truss, its strength and tension were evenly distributed by the short chords I added on the top. 

side view

top view

Bill of Materials - K'Nex pieces

Height: 5.875"

Length: 27.028"

     I used colors to differentiate the various chords I added. The yellow chord is 3.375" long; the red chord is 5" long; the black chord is 1.25" long.

    About the gusset plates, I used three types of those plates. Two of 360' gusset groove plates could connect the top and bottom truss in the middle. And when I thrusted a 90' gusset plate into a 180' gusset groove plate, the mixture gusset could connect the rest of members. 

About changes

      At first, I tried to make a bridge with arch. But end up with failing. May be because the arch bridge can not be done with K'Nex pieces.  So I started to make a K truss bridge and I thought that it shortened the lengths of the compression members compared to the other trusses. The thing I changes of K truss was I added two short chord under the middle K truss. ( like the picture shows below) 

 The reason why I did that is because this two black chords could support the top better. 

What I learned from K'Nex is the material I chose can limit my idea of bridge design. But I also also learned how to those prescriptive chords and gusset plates to build different shapes of truss bridges. 

- Yilei Jiang