Week 8: Analysis Process

During this past week in engineering lab, my group and I worked a lot with numbers and calculating stress and compression of each joint and chord using trigonometry and a method called “method of joints”. For this, we first did our calculations by hand using a lot of physics and math to find the tension forces at each gusset plate. We then entered the dimensions and weight applied given to us into an online system created to calculate all of our hard work in the click of a button. Although the numbers we got from the online system didn’t match our numbers identically, we soon found out that they were simply multiples of the numbers we calculated. This coming week my group will create a new bridge that can span 3 feet, with the ideas that we have learned from our previous bridge.

            I think that this method of joints would be sufficient for calculating for a real bridge. In the real world the bridges we build have to be tested somehow, and a lot of the times, hand calculations would need to be done for them. I would like to further analyze maybe the different ways that this tension and stress can be relived, and how the design of the bridge can affect the forces acting on the bridge.

Kelsey McSorley

Week 7: Bridge Results and Analysis

        This past week in lab we tested our first truss prototype.  Melissa and I had toyed with the bridge design for some time before deciding on a simple design that consisted of one through truss with X’s in elevation and horizontal members in plan view. We felt that, although rough, we would see how the bridge performed to determine our next steps in design. Our initial plan was to focus on keeping the cost low, however we found that the weight supported did not exceed expectations as we hoped. Therefore, last minute alterations were made. Right before testing, we added a deck truss that followed our gusset pattern and included X’s on the outer plates, to prevent the bridge from failing from middle compression. The reason for this addition, from conclusion of trial and error, was that the weight needed to be dispersed to the outer edges. Although our theory succeeded in testing, our results were not impressive. Our final bridge cost $320,000 and supported 19 pounds.  Ultimately, our bridge failed at an outer gusset point, which was disappointing because much of our design was contingent upon the success of our gussets.

        

        For this week, our team needs to analyze our bridge designs through testing with thorough tension and compression measurements in order to modify and refine our final product. WPBD was a great tool because it provided us with those calculations, which allowed us to make modifications that affected both cost and strength efficiency. 

Chelsea Moss

Video of Bridge Testing: Week 6

Week 7: Bridge Results

This past week in lab we got to test the 2 feet bridges we built. Our bridge had a fairly simple design, following a concept I learned from the WPBD; Simple is better. It was a basic X truss across the sides that included an under truss. The idea behind the under truss was that It would help disperse the weight to the outside members. The under truss worked exactly as I expected. Our bridge broke right where the under truss ended. Our bridge only held 20 lbs. I was disappointed with our bridges performance but I was proud that it did not cost an extraneous amount, only $320,000. Another thing I noticed was that many of the bridges experienced the same failures. The Knex gussets are the weakest point on the bridge and through much testing I noticed that the arrangement of the gussets on the bridge mattered and could affect the failure point by several pounds. All the gussets alternated sides starting from the center covering the weaker point

I truly liked our final design but I knew deep down that it just wasn’t going to hold a lot of weight. I spent many hours testing a building bridges but it was hard to do without knowing where the compression and tension forces were and their magnitude. When working with WPBD one could look at the numbers given in the tension and compression columns and deduce where changes could be made to make the bridge strong and where beams were not being utilized at all.  This information can easily be found using trig. I know a main factor in tension and compression calculations are the angle in the triangles. So I would assume in the calculations the angles would be essential. Other than that I am not completely sure and can’t wait to learn Wednesday!

Melissa Mercado

Week 7 Assignment: Analysis desires

During this week in lab my group came in with a design that had been previously tested but we knew we needed to make stronger. The first thing we did was added a deck truss to our original design because we knew that the weak spot on the bridge was the gusset plates in the middle. The deck added support for that area and gave it extra strength. When we tested the bridge we found that it held more weight with the deck, in the end holding about 19 pounds. The cost of our current bridge is about $320,000 so getting the cost down is also something that we need to do. This coming week we will be brainstorming our ideas about the 3 foot bridge we will be designing in the upcoming weeks, taking the things we learned about our previous bridge and working from there.

If I could know any numbers for this project I would definitely want to know the compression and tension forces (just like in WPBD) at each gusset plate. It seems like many of the problems are found at the gusset plate and so that’s where I think the most research and calculations would need to be performed. I would also want to know maybe if there is a way to calculate the maximum weight that a bridge could hold with certain values.  

Kelsey McSorley

Week 6: K'NEX Build Process

      Unfortunately, due to personal health issues and concerns, I was unable to participate in last week’s lab. Melissa, Kelsey and I met and filled me in on last week’s instructions. From what I understand, both of them built individual, full-scale bridges, while keeping in mind the final objective of the most successful cost to weight ratio.  Although I was unable to participate in this lab, I collaborated with Melissa over the week to enhance her bridge. Through trial and error, we discovered that the angle in which the gussets are arranged provided a more stable product. Our meticulousness in this effort also promoted symmetry throughout our entire design. In testing, I believe this change was able to add three more pounds to its stable condition without adding any more components.

      My opinions about WPBD compared to K’NEX remain the same. Both provide very different methods of construction. WPBD provides a virtual experience, whereas K’NEX is completely tangible. WPBD operates in a way that uses proposed materials and beam sizes to appear as realistic as possible. The results from testing have induced accuracy within the force/compression readings, which, upon careful analysis, can be used to further success in future designs. K’NEX, on the other hand, is limited in its materials but can be physically tested to its limit and thus analyzed from its breaking point. Also, one major difference in provided materials is that WPBD lacks gusset plates. Gusset plates are essential to a bridge’s construction as they join members of a bridge together yielding stability. 

Chelsea Moss

Week 6

This past week during lab we got to experiment with the Knex a second time. We were asked to build a bridge that we thought had the best cost to weight ratio. Kelsey and I designed separate bridges. I decided that I was going to try and create a simple design with the smallest length of members to lower cost. I did not have time to test my bridge during class but I did bring my bridge home to experiment and fix it. This week I have been working on a new design that will lower cost but maintain strength.

My opinions about the differences between the WPBD program and Knex have not changed. However, I see many differences between working with and designing a real bridge and a Knex bridge.   Knex limit the types of beams, members and gussets you can use. When building a real bridge a person can use any types of beams, gussets and members they want, in any shape or color. Plastics also react and bend differently than steel which is the most common material used in bridge construction. The differences between the materials also determine how they will react to outside forces like inclement weather and wind gusts. Also when someone isemplyed to design a bridge they are often given a time contraint I feel these are the greatest  and most important differences.