Week 9 Term Review

This past week we completed our final three foot bridge span and tested it. In the coming week we will work on A4 and submit it before class in week 10. The only major accomplishment this week was that our bridge was able to hold 5 more pounds that we had anticipated. We are facing no major issues as a team.

I think that each goal was met and exceeded through the course, if I were to pick one goal that I wish we had more time to explore or would have gone more in depth with I would say it would be forensic analysis. The least beneficial goal was the planning, I understand the need to plan and using the tools we were given at the end of the course I can see why planning is useful however going through the course I thought that planning was not beneficial and most of our discoveries were obtained by trial and error. Once we had these discoveries and were given the mathematical tools our discoveries were confirmed and we were able to understand why. I also feel that bridge designer was good for the simple bridge but it did not meet my expectations when it came to the group knex design. The most beneficial parts of the course were the physical modeling and teamwork aspects because we were able to test a variety of ideas and then collaborate to make what we felt was the best design. In the future I would give a better introduction to WPBD also I would have a block of wood to resemble the car to make sure that all designs meet the given specs.

Week 8: Bridge Process

This past week the group built a bridge that spans 3' and has a hollow tube of 3"x2" running through the center of the bridge to meet the criteria for the second KNEX bridge design.  Using what was learned from the truss analysis the group put together a bridge to use for the test.  The group did some practice tests on the design and made changes to better the bridge.  This next week final adjustments will be made to the bridge and it will be tested using the same set up as the 2' bridge.

Each week this term was a learning experience.  I have had some experiences with trusses and how they work through building buildings but this course certainly taught me many things about trusses and bridge designs.  I realized how important a efficient cost ratio is for engineering projects.  WPBD helped me to get started with this concept, but the hands on experience with the KNEX certainly showed how many ways a goal can be met and how different the cost ratios can be.  The truss analysis helped me to better understand how trusses displace a force.  This will be helpful for me moving forward, and I feel that it gives me an advantage over other students who have not had this opportunity yet.  Through the movies and background history provided in class I realize the importance of engineering and safety.  One little mistake can cost hundreds of people their lives.  It certainly makes me double check my work when I am creating designs and ideas.  After learning all this it makes me wonder how the bridges that are in existence now will hold up with the weathering and increased loads applied to them by traffic and things done in an effort to help preserve them.  There is a trade off in safety measures and added weight and cost.

Week 8: Bridge Process

In the past week our group has been working on building the best 3' span bridge possible. We have experimented with many different design options and we think we have found one that will perform  satisfactorily. In our week 9 lab we will test this bridge to see the results of our efforts. Through designinf these bridges I have learned that the bridge design process is not as simple as throwing together a structure and seeing if it holds up. I have learned about the different loads that a bridge faces over the course of its life such as compression forces and tension forces resulting from the load, and also lateral forces caused by elements such as wind. Some of the main things that i have learned though is that the one smallest issue with a bridge can cause catastropic failure. Bridge designers learn from these failures though. While hopefully these failures do not occur on a full scale active bridge, the use of breaking scaled down bridges is the best way to learn about how to improve them.

Week 8 Bridge Process

This past week we have worked to complete a bridge designed to span a 36” opening, and worked to determine ways that our bridge could be improved using the analysis tools we have at our disposal. This coming week we will work to further improve our design to have the best possible bridge ready to test in week 9. Overall I would say that we had no major accomplishments this past week. As a team the only issues that we faced were disagreements on how to improve our bridge and prevent it from racking.

Throughout the term, each week brought something new to the table and something that I had not seen before. We started out using modeling programs that helped us to learn to maximize the tension and compression forces that a gusset plate feels. In maximizing the forces that the gusset plate feels you are able to use the smallest size members possible, in many cases this lowers the total cost of the design.  In looking back at the videos the bridge failures shown in class it is clear that a bridge designer plays an important role in keeping people safe, if even one small aspect of the bridge has a flaw it can lead to a catastrophic failure and significant loss of life. I have also learned that when designing a bridge that is most efficient, that the bridge should be able to handle a load that will change over time; just as we have seem with local bridges the weight of paint is added on as the years go by and our vehicles continue to increase in size as a result increasing the load that the bridge must carry. Bridges are subject to more forces than meet the eye, there is the typical gravitational force but what many people don’t realize is the tension and compression in each member as well as the overall impact of the elements and external factors on the bridge.

A3: Fitzpatrick

1) Calculations of forces in the truss members using the Method of Joints

Truss bridge being used in calculations



The figure above shows the calculations neccessary to obtain all of the forces on the truss. They are place into an Excel doc for easy accessibility 

2) Truss analysis results

Note that the forces are equally and evenly spread across the bridge



 3) Truss analysis via Bridge Designer

4) In order for the forces on Bridge Designer to match the forces from the method of joints, one must correctly scale the bridges to the same size. If either bridge is longer or shorter than the pther in any way, the results are not going to be the same, because they are simply different bridges

5)

Once again, if this bridge in Bridge Designer is scaled exactly the same as out Knex bridge, the forces on each of the members should be near equal. If the design has been sone correctly, the forces from one side should be symmetrically equal to the forces on the opposite side. While this is usually true, something must have happened when creating this bridge in Bridge Designer, because it continues to show a force of zero on one section of the bridge, which cannot be possible while under a load from the center of the bridge.



6) The method of joints analysis is a good way to maually determine an idea for a load capacity for a bridge. breaking the desgin down into single specific pieces gives one a better chance at not making a mistake. One of the most vital things we can do to assure a better bridge is to use gusset plates with at least 3 joints on them. These joints are stronger than all the others when it comes to the load testing. While these are more epensive than other joints, they are well worth it in the long run. This program is  help when it comes to doing this.

A3: Miller

1) Calculations of forces for the truss members using the Method of Joints.

Truss Bridge used for the Method of Joints

This shot shows the calculations done in excel to determine the forces on each member.

2) Results of Analysis
Forces Acting on Each Member

Members symmetrical to one another have the tension and compression force acting upon them.

3) Replication of Bridge Analysis done in Bridge Designer

4) In order for the hand analysis to show the same results as the Bridge Designer calculations the bridge must be scaled to the same size.  In Bridge Designer each individual square is 2"x2".  The drawing that I did in the Bridge Designer does not have the same lengths as the hand drawn one I did the calculations for.  It does however have very similar results.

5)

The forces in the KNEX bridge will be fairly similar to the forces calculated by the bridge designer analysis.  The member lengths are a little different and there are less sections than the real bridge.  The forces felt by the 2 middle sections should be relatively realistic when compared to the KNEX bridge.  The 2 outside sections are showing unrealistic numbers.  While this is not the full bridge formation it should give us the general idea we need to help improve our bridge design.

6) Using the method of joints analysis allows the determination of tension and compression on individual members of a bridge for a given load.  Using this information it is possible to apply the KNEX connection strenghts to determine a failing load for the bridge.  The connectors with 3 members attached to them have the highest pull out force at an average of 35.6lbs.  Connectors with only 2 members attached suffer almost a 10lbs. decrease in strength which leaves them at 26.5lbs.  The weakest attachment to a connector is 1 member.  The pull out force for this is 20.7lbs.  With this data it is obvious that connectors should be loaded with at least 3 members to assure the highest pull out force.  There is also a possibility to determine pieces that are not giving the bridge any structural support by analyzing the results of calculations and using the pull out test information.  These pieces can be removed to decrease cost.

A3- Parker

1) Calculations of forces in  the truss members using the Method of Joints.

Truss Bridge That was used in Method of Joints

This image shows the calculations that were made to determine the forces on each member, these formulas were derived by hand when solving the truss and were imputed into Excel so that hand calculations are not necessary as the bridge constraints change.

 2) Results of the Analysis above

As you can see above members symmetrical to one another have the tension or compression force acting upon them

3)  Replication of Bridge Analysis using Bridge Designer

4) In order for the hand analysis to correspond to the analysis compiled by Bridge Designer one must scale their bridge so that the forces correspond with the values calculated by Bridge Designer. In the drawing above, each block represents 2" in length, and the nodes correspond to the connecters on the hand drawn bridge so the bridge in the image corresponds to the bridge that the analysis was preformed on, not surprisingly the results of the two analysis's are similar.

5)

The forces in the knex bridge should be similar to the forces in the bridge designer analysis. The member lengths are similar therefor the forces felt should the similar for the center two sections. the forces shown in the diagram for the sections on the outer sides of the diagram are showing non-realistic forces. The bridge design above while not a full bridge, provides a glimpse at the final product, a bridge constructed using the same sections as shown above held 49.4 lbs, this analysis is showing forces in that are far beyond the tolerances of knex with a smaller load. Also the load that I used for the knex bridge was 15 lbs, when creating an analysis multiple times I was shown a picture that did not seem right, tension and compression of zero on one section and on the symmetrical section the forces are to strong to be possible.


6) Using the method of joints analysis one is able to determine a number for the tension and the compression of members of the bridge for a given load. When viewing the information about the strength of knex connectors one is able to use the analysis to determine under what load the bridge is expect to fail and at which connector. Looking at the tensile pull out force chart it is clear that connectors with three members attached to them have the highest pull out force (avg 35.6lbs). Connectors with two members attached to them have an average pull out force of 26.5 lbs this is almost a 10 pound decrease in strength from the connectors with three members attached to them. Lastly the weakest connections are the ones that only contain one member; these have an average pull out strength of 20.7 lbs. Using this information the goal of the bridge design is to maximize the number of connectors that have three members attached while reducing the number of connectors with only one member attached. Using the analysis provides the number of pounds of force a given member has acting on it and paired with the information from the table it should now be possible to determine what members in bridge are adding cost and no structural advantage.

Week 7: Analysis Process

During the past week we experimented with some 3' bridge designs, in an attempt to come up with the best one possible. in addidtion to this search, each of us are also working on a truss analysis to help us better understand the loads and forces that a bridge goes through. By doing this, we will be better prepared and more knowledgeable when creating our 3' bridges. In the nextr week we plan to revise our plans and come up with a satisfactory final design that will hopefully perform well in the load test.

The method of joints system is a good way to better visualize and understand the physics behind a bridge design. It helps point out potential weak spots in a design and then show why it is weak. One of the biggest factors in a good bridge is its ability to resist outside force, such as wind, in addition to the loads traveling across it. This is something that the method of joints system lacks. Though this system may help one develop a structurally sound bridge, it cannot help in the question of how it will withstand outside force. If a bridge cannot handle all of these outside forces the design is no good.

I would like to see the effects of a bridge in the outside world. It is the only sure fire way to know if a bridge is going to make the cut. Obviously this is not possible to do in a full scale experiment, but it would be very intriguing to be able to run some sort of proportional small scale test. And even so, this is not a fully fail proof experimentation because it will still be hard to test the lifespan of a bridge. Not only does a bridge design have to hold up to brutal conditions, but it also has to last a long time. Finding a way to do this would be the only way to sucessfully perform a full test on a design.

Week 7: Analysis Process

This past week the group worked on the 3' KNEX truss bridge.  In this process each member is also working on a truss analysis for a sample bridge and for our own KNEX truss system.  This should help us analyze the truss and make adjustments to strengthen it.  This next week the group will look deeper into the analysis and come up with a final design for the groups 3' KNEX bridge.

The method of joints is a great way to get a general idea of how a truss system works.  I feel that it would not be a great way to analyze a large scale bridge.  Nature plays a large role in affecting how a bridge holds up.  The method of joints does not take into account the lateral movement perpendicular to the joints.  In a real world situation the wind would cause a large difference in these calculations.  On a small scale and to give a person a general idea of how a truss works the method of joints is a great tool.

I would like to be able to analyze how a moving load affects a bridge.  It would also be useful to be able to see how the material of a bridge decays over time.  Bridges should be built to last a long time and be safe.  It is important to see how the bridge would deteriorate over time.  Including wind forces would also be a large benefit.  In a real world bridge this would have to be calculated.  It would be useful to see what needs to be added to our bridges and ideas to make them actual models of a real life possibility.

Week 7: Analysis Process

This past week we have continued to work on our final knex bridge design, we have also been working to complete a truss analysis of a sample bridge and apply the same logic to our knex bridge to improve our design. In the coming week we will continue on the truss analysis and design of our knex bridge. This week we had no major accomplishes. The only issue that I see is related to post A3, I don’t believe that Bridge Designer will allow us to submit what Dr. Mitchell is asking of us.

I believe that the method of joints is sufficient for small scale or low load bridges such as foot bridges across a wet area. I do feel that while it provides good insight about what should be changed in a bridge design it does not take into account all of the forces acting upon the bridge. The method of joints should work great in a situation where effects related to nature are negligible; wind is a major factor in bridge design. The bridge needs to not only stop the wind from pushing it over but it also needs to be able to support the load of cars while wind is acting upon the bridge.

I would like to analyze how a bridge preforms over time with an increasing load on the bridge. The load of the bridge changes each time the bridge is repainted or the bridge deck is surfaced, the load also changes as the vehicles we drive change. A bridge does no good if it only lasts 5-10 years because there is no tolerance for maintenance to be performed.  As  the vehicles we drive change so does the load on the bridge and how the bridge handles on windy days. A bridge of cars is going to handle different on a windy day than a bridge full of tractor trailers since the trailer are going to be more impacted by the wind. I feel that we need a method that incorporates weather related stresses as well as stresses ove time.

Week 6: Analysis Desires

In our week 6 lab we load tested our 2' span bridges. Before the test we made a few minor modifications that helped with our cost. In the load test, our bridge exceeded our expectations. It was able to hold 48 pounds of sand, including the bucket, before ultimately failing. The bridge failed at one of the gusset plates near the middle of the bridge. We had actually predicted that it would fail in this area, so it was not a surprise to us. We plan to keep this in mind in our next design.



For the 2nd bridge design, we must fabricate a 3' span bridge that is hollow in the middle so a roadway can be placed through it. This will pose a little more of a challenge for us, because we will not be able to add cross bracing in the middle of the bridge, something that greatly increases the rigidness of the structure.



One thing that I believe would greatly help in the Knex design process would be the ability to see all of the forces acting on the bridge. If a script was generated that could hook up to a bridge and record the changing forces on the bridge, it would be very difficult to test without again. The ability  to see all of the forces in the bridge allows one to have a better idea of what parts are weak and failing or what parts are holding strong. This is unfathomable for a small scale Knex project though, because a machine capable of all that would take a large sum of time and money to create. This would be unnecessary for a small scale project like this one because of the time and money involved in something like that would make our design too expensive

Week 6: Analysis Desires

This past week the group took our 2' KNEX bridge design and made a few modifications before the load test. The group wanted to try to decrease the cost and still provide the strength that the original design had.  Our bridge managed to hold 48.4lbs which was the highest in the class.  However our cost/breaking weight was not the best in the class.  Our bridge was not the highest costing bridge in the class but it was among the top costs.  In the next test we will try to make modifications to the design to lower the cost without forfeiting the strength.  The bridge failed at the gusset plates.  The group predicted that the gusset plates underneath the load plate would break.  This was a close prediction.  The plates at the edge of the load plate on the underside of the bridge truss pulled apart.  The KNEX bridge structures week points are in the gusset plates dealing with tension.  They tend to pull apart or snap the small connection points.

If possible it would be great to be able to calculate the tensions on each individual connection on a gusset plate.  It is obvious that the plates close to the load plate on the underside of the bridge experience the most tension.  Trig functions may be able to help break down the forces along different cross members.  The fact that all connections are made at either 45degrees or 90degrees should allow for easy calculations.  I am not sure how to account for the decrease in forces toward the end of the bridge or how much force the slight bending of each individual beam takes out of the overall force.  The compression forces do not seem to be a problem.  The beams are much stronger than the gusset plates and are less likely to bow.  It is also important to figure out how the cross members from side to side strengthen the bridge.  Bridges will fail easily by racking from side to side.

The rules for next week has changed some.  The group must complete a 3' bridge with a hollow section 3"x2" for traffic to travel through.  This provides a whole new set of challenges and lots of modifications to do from the original design.  The group will get together and try to use what we have learned from the first load test to create a bridge with a better cost/breaking weight ratio.

Week 6:Analysis Desires

This week we made a few minor modifications to our bridge as we had thought about ways to improve our design before testing. This week in lab we tested our bridge to see how much weight it would hold and ours held 48.4lbs of sand, the most in the class, the cost associated with building our bridge was also amongst the highest in the class which results in a poor cost to strength ratio. This coming week we will refine our design and begin to work toward a working three foot bridge. With the success of our first bridge we have a good starting point for the second design, we just need to work on reducing the cost. As a team we are facing no issues and as an individual I am happy with our progress in the class.

With our bridge constructed using Knex it would be nice to be able to know the forces that each beam is experiencing, specifically the compression of the members that causes them to bow out. Another quantity that would also be useful to us is the force that each joint of the gusset plate is experiencing and what they are capable of handling. When the bridge fails the beams are not breaking, in some cases they are bowing out however the beam is not the point of failure, the gusset plate is the point of failure. Every bridge fails at its weakest point and in the case of Knex the weakest link of the bridge is the gusset plate, in order to determine the load that a bridge can handle we need to know the forces acting on the gusset plate. In order to calculate the force that each gusset plate is experiencing I think that we need to break the force down into its components via trig functions and add the forces but I am not sure how to take into account that the load is being spread across the structure and is not being focused to one particular point.

Week 5: Knex Process

In our week 5 lab we spent the whole class building and modifying a test bridge, looking for the strongest, yet most cost effective design. We tweaked and modified our design multiple times before we came to a design we are content with, and we are excited to test it. In our next week of lab we plan to break this bridge and then analyze what area of the design was first to fail. This will then allow us to better our design even further for the future.

There are definitely some major differences between designing a bridge with Knex compared to designing one with real bridge materials. A few of the biggest differences would be the cost of the materials obviously. Steel costs much more than plastic. Another difference between Knex and a real bridge is the ability to vary the length, size, and strength of the materials. While with the Knex pieces are set at a pre cut length, steel can be cut, bent, and modified to fit any design imaginable. One similarity between Knex and a real bridge is that the principles of truss bridge design stay close to the same, hence the reason we are using them in this course.

Week 5: KNEX Process

This past week the group began constructing different KNEX trusses systems.  The group worked together to create several designs to test and learn from in order to create a better design.  These KNEX bridges are all 2'.  The final design will have to be 3'.  The group has not had any problems designing a strong bridge but the cost is on the high side in order to achieve a good cost/load ratio.  The group will look at ways to lower this ratio in the next weeks.

My views on the differences and similarities of the KNEX and WPBD have not really changed.  KNEX has the disadvantage of only 45degree increments and WPBD doesn't account for the horizontal forces applied to a bridge.  They both are great tools at looking into truss systems for bridges and testing them.

There are many differences between a KNEX bridge and a 20' steel bridge.  The different number of materials and different design possibilities are endless for a 20' steel bridge.  The KNEX bridges are limited to the few pieces given and to the 45degree joint increments.  The way the steel bridge joints are fastened at the gusset plates have huge variations in options as well.  The KNEX bridge does have a few advantages though.  The KNEX bridge can be tested and rebuilt without any cost.  A 20' steel bridge costs a lot of money to make and it must be right the first time.

Week 5 Knex Process

This week in lab we shared our designs with our team members and we decided upon the best bridge design and we constructed our design. This coming week we plan to test our design and to make improvements with the pieces that we have. Each of us have also agreed to look into other designs and think of ways that we make improvements to our design for the class competition. Major accomplishments this week include designing a bridge to test and fully assembling our design.  The biggest issue we face is quite minor and that is agreeing on who will be responsible for the bridge.

My views on the similarities between West Point Bridge Designer and Knex have not really changed after working with Knex for a second week. I still feel that they are similar in that they can both be used to replicate a bridge. The difference between the two is that you are limited in the options that each has to offer, I also believe that they differ in the forces that they take into account, West Point Bridge Designer is solely based on tension and compression whereas Knex allows us to view forces that act horizontally on the bridge.

The differences between working with Knex and a real bridge are immense. The shear number of options for materials on a full size bridge is overwhelming such choices that have to be made are the strength of the concrete used for the footings, what material will be used in the webbing, how the materials will be fastened together whether it be welding, riveting, or bolting, then you have a decision with what material will be used to cover the driving deck of the bridge. I think that Knex are able to give us a good idea at how to go about designing a large scale bridge but I feel as if there are factors that are still out of our league to discuss. The possibilities are endless when making a bridge out of steel because the steel can be bent, cut or shaped however is desired, with Knex we are limited in what we can do because of beam length and the angles that the gusset plates allow us to use.