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