Week 10

Last week was the week where our final bridge designs were tested, the goal of the all the designs was to have the lowest cost to weight ratio. Our bridge won the competition with a ration of $8,542 per pound. The lab period was used for only the competition this upcoming lab period we'll have a closing discussion of what we did during the term.

I believe that this term was very beneficial towards my major, it helped me consider different situations that I will eventually encounter in my academic as well as my professional career. This simple way of modeling bridges is an easy way of viewing one of the most basic ideas in engineering, trusses. These hollow structures are everywhere, from the crane that is building the new business building to the chair im sitting on. I think that by constantly experimenting with different structures I was able to better understand the forces that are constantly affecting a bridge. I think one of the least beneficial things of the course was the fact that we could only use a simple truss design. I would have enjoyed it if we were able to use arches and hanging bridge designs. This would have been a perfect introductory course on bridges and basics to civil and structural engineering. Other than that I think that this freshman design project was a good experience, I learned a lot about bridges and the way they can be built and can fail. 

A4-Weldon/Hidalgo/Almendariz

Bridge Report

Figure 1: Final bridge design.

Background
                The bridge design competition is a lab module that tests different truss designs. The lab brings together computer modeling, physical modeling, forensic analysis, static analysis, and teamwork to build a bridge. The design process starts with computer modeling using programs like West Point Bridge Design and then the design process moves to physical modeling using Knex pieces to build the bridge you had earlier designed. The analysis tactics are used at certain intervals to help increase one’s understanding of how to build the bridge to its full potential. The main goal is to build a bridge with the lowest cost to weight held ratio.

Design Process

            As we started to build our final bridge design we started out by modeling it after our first 24’’ design. It was a simple truss design with two levels of trusses the top one shorter than the other.  One of our main goals was to replace the 360° grooved gusset plates with alternatives that would eliminate the weakness created by the connections between two of the gusset plates. With the help of the analysis of tensile pull out forces of the Knex pieces we wanted to optimize the amount of force each of the gusset plates experienced

(http://www.ce.memphis.edu/3121/projects/Project_1/fall_11/knex_pullout_force_f11.html). As we continued to work on our design our first attempts were failures. We tried several modifications one of them was to use the normal 360° gusset plates buy connecting the members sideways rather than the conventional way. This didn’t work as we planned because we didn’t consider it twisting sideways which it did.

The role of the individual projects such as West Point Bridge Design, Truss Analysis, and Individual Knex Design is that each helped to bring different views and discovers to the group. It allowed us to work off both what we discovered on our own and what others in our group discovered. This made it so many ideas could be brought forth and combined to make the best possible design. For example with the truss analysis it quantified the specific forces that act on a bridge. This helped better our design by purposefully orienting the direction of the grooved gusset plate connections a direction that counteracted the forces acting on the bridge.

In choosing our final design we decided to go two ways and combine them. The first one was to create a very dense truss that was expected to be expensive but also that had a higher resistance. The second was the original “arch” truss design, which had proven to be effective in the first competition. The only component that was constantly being modified was the under truss, this structure wasn’t a complete idea when construction started it was more of an idea of how different gusset plates and connectors could be combined. Eventually we came to the final design by using the 360° gusset plates in any way we could. The load at which we predicted the bridge to fail was 40 lbs, we predicted this because of our previous experiences with the bridges, our first bridge’s load at failure was about 30 lbs and since we used the same set of pieces we didn’t expect our bridge to resist more than 40 lbs. 

Final Design

          Below is the plan view of our design the tilted rectangles and blue circles are 360° gusset plates, all the white circles are two 360° grooved gusset plates connected to each other. 

Figure 2: Plan Drawing

In figure 3 a visual depiction is shown of how the gusset plate was used in the middle of the truss.

Figure 3: Individual truss section

        Our final Design was not very conventional because it included an intermediate truss which helped distribute the downwards force experienced by gravity. The truss helped resist more tension that is felt in the bottom part of any bridge. Below is a separate drawing of the truss that went in between the main structure.

Figure 4: Intermediate truss

       Figure 5 and 6 are elevation views of our bridge. This particular view was challenging to draw because of the intricacy of the design.

Figure 5: Elevation drawing

Figure 6: Elevation view.

Below is the bill of materials.

Figure 7: Bill of Materials 

Testing Results            
           Our bridge was able to hold 102.6 lbs before failure occurred. The bridge failed at the gusset plates at the center of the bridge. The bridge split right down the middle. The failure was not caused by a member slipping out of a gusset plate as was observed earlier. Instead the plastic connector itself cracked from the force created by the weight. The crack of this one gusset plate caused the other gusset plates on the same plane to slide out. As Figures 8 and 9 show the split was right down the middle where most of the force was experienced. 

Figure 8: View of area that broke.

Figure 9: Bridge after failure.

Conclusions

            The group’s final bridge design model behaved completely different than expected.  Originally we predicted the bridge to hold about 40 pounds and not have a good cost to weight ratio.  As stated previously the main focus when designing the final bridge model was it’s strength.  We decided to completely ignore the concern of keeping its cost down and let our creativity focus on the structure and strength of the bridge.  We tried dividing the weight resistance equally throughout the bridge to avoid putting excess tension on a single portion.  This way we were able to build a nonconventional bridge with an interesting structure.  Although we focused on the bridge strength we underestimated its strength by hypothesizing that it wouldn't hold more than 40 pounds.  Our biggest concern was the fact that the bridge had so many members and connections.  We thought that connections would create weak spots that would weaken the bridge.  Therefore we were expecting it to collapse by braking in the middle.  During the competition the bridge had a surprising behavior proving our hypothesis wrong.  The bridge ended up being able to hold 102.6 pounds.  Throughout the competition we didn’t see any bending or twisting in the structure of the bridge.  Although we were able to pull the biggest weight resistance we didn’t expect it to be able to have a good cost to pound ratio.  By ignoring it’s cost during the development of the design we ended surpassing all the other bridges cost by pulling a cost of $826,500.  Due to its high cost we didn’t expect at all to be able to pull a reasonable cost to pound ratio and predicted it to be $21,913.  It is for these reasons that we were surprised to know that our bridge won the competition by pulling the best cost to pound ratio.

Future Work

           Although our bridge design model was successful and won the competition.  If we were given the chance to modify and improve we would make some changes to lower its cost.  We would increase its scale by using bigger members to create the same 36” and not modify its structure and shape at all. This way we would use a less members and connectors reducing its cost significantly and either keeping or improving its strength.  We think that connections create weak points in the bridge and by decreasing their number the bridge would strengthen the bridge.  Further more experimentations and testing would need to be perform to see the effect of this change in its strength.  Also we misused 360 gusset plates in the sides of the bottom level of the bridge. Figure 10 shows the inner design if the white gusset plates had been replaced by yellow 180 plates the cost would have been lowered significantly. We would not make major changes any changes in the design and structure of the bridge model because we think its not necessary.    

Figure 10: View of bottom section before top is added.

Figure 10: Cross section of bridge.

Week 10

Week 10

            In the previous lab section we got the chance to test the group’s final bridge model.  All groups competed against each other to try to attain the best cost to cost to pound ratio.  Our group didn’t expect to win the competition originally because we knew that our bridge was really expensive and we didn’t predict it to hold more than 40 pounds of weight.  It was shocking to first see that the bridge was been able to hold so much weight and it wouldn’t collapse and best of to see that we were able to pull the best ratio of all the class.  Our bridge was able to pull up a cost to pound ratio of $8542.88.

            I found this Engineering design project to be my favorite of all the year.  I liked the way that the course was structured throughout the whole term and dividing every assignment in a really easy and effective time manner.  This was really helpful because it divided the workload in reasonable time amounts that will not pill up everything for the last minute.  I found all the material explored in this course worthwhile and really interesting.  I think that the way that they were set and their structure were essential for us to have a basic understanding of bridges and be able to design one.  Although I had some little knowledge about bridges I did learn some really interesting and important material through this course.  I think that the most significant piece of knowledge that I learn was by using WPBD.   I found this program to be really interesting an efficient by letting us know what work the best for bridges.  I was able to test different bridge designs that I though about and was able to know which structure worked the best.  The least beneficial topic explored was the one about teamwork because I think that teamwork skills are learning through each experience.  I don’t have any significant suggestion for the improvement of this design project.  I think that all of it was really well structured and planned.   

Bridge

This is the bridge that was used for the final competition.

View of the cross section.

View from the side.

     Our bridge was constructed of 773 Knex pieces. The total cost reached $876,500.00. The bridge finally gave out at 102.6 lbs. Failure was dude to a gusset plate snapping. We believed that failure would occur at the center because this is where the weight is centered and this was the location of the broken gusset plate. The cost per weight ratio came to $8,542.88 per pound.

Week 10

     During last week's lab period we tested our final bridge design. The bridge was tested to how much weight could be held. The goal was to have the least cost per pound held. Our bridge had a ratio of $8,542.88 per pound.
     In the upcoming week our team will have completed our A4 assignment. In lab we will go over an overview of what was done and taught during this term.
     Major accomplishments for our group was that our bridge held the most weight and had the best cost to weight ratio.
     I do not believe there are any issues facing the team now that the term is coming to a close.
     Yes I do believe I learned something worthwhile about each of the topics for the course goals. I feel that I learned more on teamwork, which is very essential to the design process. I also learned a lot about planning, computer modeling, static analysis, and physical modeling. Each step took in the lab helped lead to the next and give us a better understanding of what we were designing and building.
     I think that the static analysis was the least beneficial to this lab process. I believe this only because we are limited by the Knex pieces. Observing how angles affect the way the weight is distributed across the bridge is good knowledge to acquire, but does little to help with the design of our Knex bridge. If I showed X formations against other formations that could be designed with the Knex pieces it would be more helpful.
     The most beneficial for me was the actual physical testing of the bridge. This was the most helpful because it brought together everything that was taught to you before that point. Also because it allowed you to see that a certain cross section between the two vertical sides had to be constructed or else the twisting would occur. Physical modeling and testing gave you the ability to fully view your bridge and see how added weight affected it.
     My only suggestion is allow for more testing of the physical bridges before the final test.

By Robert Weldon

Week 8

Week 8

         Week 8 lab was really productive for the team for being able to put all members ideas into a final design.  Also it was a great opportunity for the team to test different 2 feet bridge designs that were brainstormed.  We were able to see main weaknesses and strength of each design.  The results from these experimentations will be considered for the design and construction of the final bridge design.

         I had found this engineering design project really interesting and enjoyable.  Each part of the module was has it’s own important significance and has teach me really interesting and important basic knowledge about bridges.  During the first part of the project when we were able to play around with WPBD I was able to see what structures had a successful strength.  Also I was able to play around with the building materials to be able to bring the cost down of the bridge while keeping its strength.  During this process I was able to get a better understanding of what structure designs seem to be more successful.  I learned that triangles do an excellent job distributing forces.  It is important to consider the fact that this are not the only forces a conditions to which a bridge has to survive.  We were then introduced a way to be able to calculate the tension that each member of the bridge.  It is important to mention that each method and program used during this project had their own strengths and limitations.  Finally the most challenging part of this lab was to actually put all of our ideas and knowledge into designing a bridge that would have a good cost vs. strength ratio.  

Week 9

Last week during our lab period we were asked to begin our final bridge design. Throughout the period we brainstormed and tested what worked and what didn't work. We constructed two designs that we had in mind, both of these designs were drastically different than our first design, they both involved using more single connector plates rather that the ones that have to be connected to each other to be functional. We implemented these plates by conecting the membranes differently, the memebers were connected on their side rather than their ends. Unfortunately this didn't work as planned, the bridge failed because it twisted and bent sideways. Although these designs didn't perform as we wanted them to we learned more things about how the Knex pieces can be used. As we come closer to the end of the term I can look back and actualy see how much I have learned about how to design a bridge. Many of the things that I took for granted for example the number of connections that were used in the design have a direct effect on how the bridge can support a certain load. I have also learned that the way the members are positioned also affect the distribution of the stresses of each member. The most crucial thing that I learned was how the bridge bent when it was loaded. This helped us decide on putting an extra truss in the middle of the original truss.

Week 9

     In the prior week our group was instructed that the gusset plates were able to become stronger with the increased number of connections. We then constructed a new bridge that partially followed our old design, but used far less amount of materials. The bridge proved to be to week and failed by twisting. The design was altered to strengthen the connections between the two sides of the bridge. This design wasn't able to hold as much weight and failed due to weak gusset plates.
     In the next week we are going to move the support that protects against twisting to the top of the bridge instead of the bottom. We will also test the bridge to see what its max load is.
     Major accomplishments for this week are having a bridge that follows our initial design, but with less materials than what we first tried. The bridge failures are also a promising factor as it shows that the bridge can vertically hold the weight; it just has a tendency to slide and twist on itself.
     The issues that have arisen are that the bridge it structural weak when horizontal forces are put on it. The problem with fixing this issue is that the solutions cause for a weaker bridge in the vertical forces. The best solution will allow for no twisting while at the same time not sacrificing vertical strength of the structure.
     What I have learned from the bridge design process is that everything aspect of design for a real bridge must be considered so catastrophes don't occur and no one is harmed. I learned that all truss designs are built out of triangles as these don't shift as squares and more sided shapes would. The forces on all the member can be broken down to see exactly what forces act on each member. The forces include tension and compression forces. I also learned that the weakest points on a bridge are the connections.

By Robert Weldon

Week 8

In the previous Lab we were given the chance to start playing around with online Bridge Design and work on the A3 assignment.  In the next lab we would making analysis and calculations for the angles and triangles been used with Knex.  We hope that the information provided by this analysis will help us improve our design.  We hope to be able to maximize the strength of the bridge and minimize its cost.

Both the hand and online Bridge Design calculations are not sufficient analysis for building a real bridge.  It is important to mention that there was several significant limitations found with online Bridge Design.  These limitations are expressed in A3-Almendariz.   As stated before, there are much more forces and derivable that need to be considered for building a real bridge design.   Unfortunately these calculations are only made for the side part of bridge and the calculations for a third dimension is ignored.  Also in order to build successful bridge we need to consider much more outside factors than the downward force resistance.  We need to consider what materials we would use, in order get a good ratio between price and strength.  Also we need to consider the weather, type of ground, wind forces, etc. from the location where the bridge is going to be built.  There needs to be a further study, calculations and testing to be made before been able to come with a successful real bridge design.  

A3-Almendariz

1.

2.

Member	Force (N)
TAC	22.23
TAB	-31.44
TBC	31.44
TBD	-44.46
TDC	31.42
TDE	-31.44
TCE	22.23
Total Weight	44.45

3.  

4.  Using Online Bridge designer is an easier and faster way to calculate the forces for a bridge design than calculating them manually as before.  Although the program was really versatile for calculations, there were some important restrictions found.  Online Bridge designer had restrictions involving the weight added, the scaling of length of trusts and their angles, and position of nodes.  There was a small window for choosing the load been added, it is limited to multiples of five.  We would not be able to know exactly the length of each trust that we are using and the angle between them.  These restrictions made it difficult to know were was the right position for placing the nodes.  In order to be able to correspond the results from part 1 to bridge design we would need the right scaling for each component and be able know and plug exact numbers for each components.  It is important to note that although online bridge design had it’s restrictions, the calculations given were reasonable close to the calculations done by hand before. 

  5.

While trying to replicate our bridge design in online Bridge design program a big restriction was found.  Online Bridge Designed required relating the numbers of nodes to the number of members.  Our original bridge design had to be altered in order to get it working with the program.  We were forced to take some members out and a node out.  It is for this reason that these calculations are not accurate.

6.  The data provided by the results from the testing of Knex Joints are really useful for the final design.  The results from the testing showed that that the more joint socked we used, it would create a stronger structure.  We are able to know and give an estimate of how much force each connector will be able to resist before it collapses.  We would consider this data for improving our next bridge design by trying to maximize it’s force resistance.    

Week 8

     In the prior week's lab, we learned what the Method of Joints is. Through the Method of Joints we began to construct the tension and compression forces that appear on a given bridge with constraints as to the height, length, and load on the bridge. This analysis helps to show what angles create better triangles that can hold more weight.
     In the coming week our team will begin to analysis the triangles and angles used in our Knex bridge, same with the member lengths. We hope to find that we can cut costs in certain areas, and increase the overall integrity of the Knex bridge.
     The major accomplishment of the week for the team was successfully able to learn and understand the Method of Joints and apply it to the constraint given 2-dimensional bridges and a 2-dimensional version of our team's Knex bridge.
     Issues that may arise in the up coming weeks include unable to find the right members or members combination that increase the strength of our bridge. It may be that our bridge is already built to its full potential and nothing else can be done. It may also be hard to decipher our analysis of our Knex bridge using the method of joints.
     The Method of Joints is not a sufficient form of analysis because it does not account for multiple loads on the bridge in areas other than the middle of the structure. It also does not account for horizontal forces such as wind and rain, which can add to the forces acting on the bridge. It would be a sufficient form of analysis if outside factors and change in the loads could be accounted for. To further analysis the bridge, tension and compression strengths of each member will need to be known to know what their breaking point is. What may help assist in this analysis is a more advanced program than WPBD, but one that measures the same information.

By Robert Weldon

A3-Weldon

 Method of Joints

     The necessary steps for converting the hand analysis that was done to a format that Bridge Designer can use to give you the same results is a method of scaling. Bridge Designer gives you a grid to work on, you can set any number of inches to each square that fits the user. I set each square equal to 2 inches. Doing this made it possible for me to find the correct ratio of distance for all the nodes.

     One problem that we found using Bridge Designer was that it required the user to relate the number of nodes to the number of members used in the bridge design. Our bridge had more members than nodes so we were unable to test our actual design, but a similiar version was used.
     This information about the method of joints greatly helps with the final design of our Knex Bridge. We will be able to see what the angles of the connectors produce in terms of tension and compression of the certain member that is in that location. We can then compare this information to the failure point of each size of Knex to see which piece will be best suited where, while still maintaining the design of the bridge and increasing its integrity.

By Robert Weldon

Week 8

During las week's lab we were introduced with a way of analyzing the forces on each part of a truss. This method is called the joint method analysis, this method basically analyzes the force on each junction. Using basic trigonometry the forces of tension and compression can be calculated. We spent the whole lab period doing calculations and figuring out how these forces will help us produce the best design possible for the final project. This week our focus will be to collaborate, and use the joint method analysis to improve on our current design and see how the design changes with the added length.

This method of analysis will be useful but not in all the situation we may encounter. Unfortunately this method of analysis only considers the front part of the truss, ignoring its third dimension. This method is also a very simplistic way of considering how the force acts on the truss. It considers the force to be even at a certain point and fails to consider it coming from more than one point, this will change the results of tension and compression forces. The material which the bridge is constructed is also very important when considering the forces that it will actually support. A detail that will have to be kept in mind is how the actual KNEX react with the forces that are added to them.