Week 9

This past term my knowledge of bridge design has increased tremendously. Before coming into this class I knew that bridges had to be designed with specific angles, placement of the beams, and width and length of the beams. But after doing calculations by method of joints, and by using the WPBD I was able to see all of the different factors affecting bridge design. Force, tension, and compression are all taken into account when creating a bridge. Also, with the challenge of building a bridge with a low cost per weight lifted ratio, I have learned to think more critically about creating the best design. This class has given me a sample of what the bigger picture is actually like. Despite not being a civil or architectural engineering major, this class has taught me that no matter what we are creating, one little error in analysis can be the difference in saving lives depending on what the creation is.

Last week we had to begin testing our new 3-foot bridge designs. We initially started off with two different bridges, but neither could lift more than 17 lbs so it was not as well as we hoped. Our new goal is to modify our bridge and create the best design for a final testing.

Week 8

This week in class we discussed the forces that we calculated over the week and what they meant. We learned and understood the fact that for each gusset plate, the more chords are attached, the more force can be applied before the chord slips from the gusset plate. Then we received the constraints for our final bridge. The bridge had to be 3 feet long and be hollow long ways on the inside by the dimensions 3 inches by 2 inches. This made the actual designing of the bridge a little bit more difficult since we could not actually have chords cutting across the middle of the bridge. In class we made a bridge that only held 17 pounds. Through out the week the bridge has been modified and will hopefully be able to hold more weight.

Bridge Process

Throughout this term I have learned a lot about bridge design. When I first started WPBD I learned that there are many different ways that a bridge can be build. There are many types of measurements that go into bridge building as Ill. With this I first noticed the tension and compression forces and worked with WPBD so that the forces would not prevent us from having a functioning bridge.

When I started using Knex I became aware of the real building restraints that come with building a bridge. There are only so many ways that the chords can be arranged with the gusset plates. Not all the angles that I wanted to work would work and so I had to adjust accordingly, changing up the size of the chords and where they were placed.

I would have to say that I learned the most from the calculations we did to analyze the forces upon each of the chords that made up the bridge. With the knowledge of these forces it was easier to build the bridge. Since we knew which chords had no force acting upon then we knew that we could remove them. This knowledge helped my group to improve our final bridge design.

Week 9 - Bridge Process

Before going into this class, I had no idea what a bridge design is all about. In fact, I didn’t even know what a Truss Bridge was. But as the term progresses, I have learned so much about bridge design. First of all, I now understand that a bridge design requires many calculations and planning ahead. I have learned how to construct a “serviceable” truss bridge via WPBD along with adjusting the members to lower the cost. Then, I was introduced to K’nex—building a more realistic bridge along with calculations. The most helpful calculations that I have learned in this course is the “Method of Joints”. This truss analysis allows me to understand the tension and compression forces, and how they play a major role in the designing process. In addition, online Bridge Design is also a great tool to calculate the tension and compression forces. Finally, I have learned that it is important to make accurate measurements and calculations because a slight calculation error can become a huge problem in the long run.

Last week in class, we worked on our three-foot-long bridge along with the new constraints—hollow by 3 inches wide and 2 inches tall. We constructed two bridges during class, but neither of them turned out well. The goal for this week in class is to redesign and construct a final bridge within the constraints.

Analysis Process

This week in class we were introduced to the "Method of Joints". It allowed us to perform an analysis of a simple Knex truss bridge. Using the calculations of this method, the forces acting upon the bridge and the force of each of the members were found, and also the tension and compression of each member.  

I believe this method of analysis is insufficient because it disregards the outside forces acting on the bridge such as the weather, deterioration, and the weight on the bridge. Also, the force being taken into account is the vertical force. Forces come in all directions, such as wind would be a horizontal force. I would like to learn more about the impact that adding a new member would have on the bridge, and the strength that each member has, so that we know which member is unstable and causing the bridge to collapse. 

A3 - Varghese

1. Calculations of the "Methods of Joints"

2. Results of the truss analysis

Tension => +
Compression => -
FAy = 44.45 N
FAx = 44.45 N
Tab = -61.02    Tac = 40.83   Tbc = 61.02   Tbd = -81.66   Tcd = 61.02   Tce = 40.83  Tde = -61.02

3. Bridge Designer Replicate

4. Hand Analysis vs. Online Bridge Designer
When conducting a hand analysis it is possible to make a rough sketch where the members are not entirely equal to one another. On the Bridge Designer the length of each member and angles must correspond correctly in order to get the right scale quantities. Bridge Designer also corresponds length 2x2" for each block.

5. Bridge Designer Model of Knex Truss

6. Given the test information about Knex joints, I made some interesting observations regarding the pull of force of connectors and the tests. It gradually begins decreasing towards the midway point, but then increases as it passes the midway point. I also noticed that the pull out force increases with the increase in connectors for each mode. With this information, I can see that the number of connectors to the mode correlates to the pull out force for the bridge sustainability.

Week 7

This week in class we were introduced to the calculations that allow us to analyze each member of our bridge. We spent the majority of the class period discussing the calculations and working on the calculations to make sure that we all understood what that calculations were and what they all meant. We also worked with Bridge Designer. We made the bridge that we had to calculate the forces for and compared the forces we calculated with the forces that came up on bridge designer. The calculated forces and the ones given by bridge designer were relatively similar.
Now we can use this new found information to build our next bridge. This information will allow us to remove the beams that do not have any forces on them as well as add beams to better distribute the forces that are present. 

A3 - Zhu

1. Method of Joints

2. Results of Analysis

3. Online Bridge Designer Replicate

4.

In order for the lengths of the hand analysis to correspond to online Bridge Designer, the lengths of the members must be scaled equally to the Bridge Designer. In Bridge Designer, each grid is 2x2x2 inches. In my case, the length of my bridge needs to be 36 inches; so on Bridge Designer, my bridge needs to cover 18 grids. Then, the amount of load I need to add is measured in Newtons—20 pounds is approximately 90.7 N; therefore, I added 90N to the midpoint of the Truss.

5. Bridge Designer For Knex Truss

The automatic calculation feature on Bridge Designer has calculated the forces on each member of the bridge. According to the logic I used in #4, each grid should be 2'', and the load should be measured in Newtons.

6. Final Analysis - How to use this analysis to improve the bridge design?

The calculated tension force and compression force will enable us to improve our cost to strength ratio of our bridge. If there's too much force on certain members, it means that we have to adjust the location of the pieces and perhaps change the design up a little bit. On the other side, if the members show little to no force, we can eliminate them to lower the overall cost. According to the Knex joints web page, the more members that are connected to a connector, the more stable the bridge. The pull out force increases as the number of members increases. Using this piece of information, I learned that we should change our design a little bit so that most of the connectors have more than one members going in an angle less than 90 degrees.

A3-THOTTAKARA

Hand Analysis of Bridge

 








































 Bridge with all Calculated Forces


Bridge Made in Bridge Designer



To get the results of the hand analysis to correspond to online Bridge Designer we had to try to get the member lengths and angles as accurate as we could without actually being able to measure it out. Also since in my calculations I had changed the units of the load to Newtons for force I had to make sure that I put the Newton value in for the load instead of the pounds. By scaling the bridge on bridge designer to the best of my ability I was able to approximate a theoretical value for all the forces acting on the bridge. Comparing the values I calculated to the values that were given in bridge designer it seems that our calculations are relatively accurate. Some of the forces are slightly inaccurate; this error probably came from the rounding done during the hand analysis. Also, the “scaling” of the bridge on bridge designer could have probably been a little more accurate.

Knex Bridge without Forces




Knex Bridge with Forces


For our Knex truss that was made using Bridge Designer the load that was applied was measured in pounds so all the forces are according to that unit. Other than that it is the same as the other bridge that we made in bridge designer. We approximated the lengths of each beam as well as the angles between the beams as well as we could to get the approximate theoretical force that is applied on each of the beams. This information also tells us with beams have compression forces and which have tension forces.

The information given to us by the hand analysis and the testing information about Knex joints will enable us to be able to build a better bridge. The hand analysis and bridge designer tell us which beams will break because of too much force on them. It also tells us which beams have no force on them. We can remove these beams from our design since they are not significantly helping the bridge. With the testing information about Knex joints as well as the calculation giving us the forces we know how much force it will take for a beam to slip out of its gusset plate. This will help in the aspect that we will know how to most efficiently arrange the beams and gusset plates so that the bridge will be able to hold the greatest amount of weight without collapsing from too much force or from beams falling out of the gusset plates.