Analysis Desires - Hudson

When testing the bridge last week, we had an inexpensive bridge that only held 18 pounds of sand compared to 45+ pounds of other bridges that were more expensive. When we redid our bridge to make it stronger it only held about 10 more pounds and cost about twice as much, so we reverted back to our old bridge. This process - test, rebuild, test, unbuild - took the entire 2 hour class period. Clearly, this is a rather inefficient method of designing a bridge.

When using WPBD it was easy to see the ratios and the cost in an instant when you changed your bridge and you could change your bridge time after time, start new bridges, continue old bridges, and just all around get more data in two hours than by hand with the knex. For this reason, I think it would be nice to have a simple way of calculating cost-load ratios and it would help to know approximately how much stress certain types of triangles can take before something snaps. This would help tremendously when designing the bridge because if certain triangles at certain angles hold more weight effectively, it would be easier to design a bridge using those triangles and then test it and tweak it than just blindly assembling knex pieces and hoping for the best.

This week I hope my group can figure out basic ways to analyze our bridge design and possibly attach some numbers to it so that between this week and next week we can rebuild and/or tweak our bridge design so that it is more effective overall.

Analysis Desires - Lester

During Week 6 lab each group tested their bridge design using buckets of sand. Our bridge was least expensive, but only held 18 pounds. This does not lead to an idea cost to load ratio. We will modify the design before and during Week 7 to have the ratio be more ideal, then we will once again perform stress-tests on the design. Some extra data would be extremely helpful in this rebuilding process. In WPBD, it was easy to stress-test the bridge over and over. After breaking the bridge would reset without any effort. However, Knex pieces tended to snap and break, or pieces would fly far away and be difficult to recover or reassemble. In short, it is not a good idea to continue testing one bridge endlessly. Having numbers associated with the design would really help the testing process, as physical tests wouldn’t be so essential. The following knowledge would be helpful in the design process.

Knowing the weight that one triangle holds, depending on connection angles, gusset type, and length of members. Finding the amount of pressure that can be put on one gusset plate before it breaks. At the present time, I cannot think of a method for finding these numbers. Perhaps doing independent weight-bearing trials for many different types of triangles and compiling the data for the class to use. If these two pieces of knowledge are known, a design with an efficient cost/load ratio can be made without as much time consuming trails and rebuilding.

Analysis Desires- Durkin

It would be incredibly helpful to be able to determine the amount of stress on each piece of the bridge, specifically the joints as the joints seem to be were the bridges are slipping and breaking most often. In other words knowing the compression force versus strength ratio as well as the tension force versus strength ratio for each member and joint would be incredibly helpful. These would be very help because they would help our group determine which pieces are unnecessary and which are carrying the greatest load.  The unnecessary pieces could then be taken out which would help to reduce the cost of the bridge.  Steps could also be taken to help better distribute the weight on each member and joint of the bridge in order to maximize the carrying capacity of the bridge. 

            This past week our group tested a bridge and found that it was not very stable, since then we revisited the design of our bridge.  After our first test last week we designed a new bridge that was cheaper and more stable which we plan to test and further revise in the weeks to come.  This coming week we will begin those revision after testing the bridge again, we will also be trying to see what has worked for other teams and how we can include those aspects in our own design in the hopes of becoming closer to our final goal of having the bridge with the smallest cost to carrying capacity ratio.