Week 4- Kyle Hayes

This week we gathered our group’s designs and tried to find the best parts of the three and create an even better bridge. we did manage to cut a few thousand dollars in cost, down to around$240000. We wanted to make a bridge that was only either a top truss or a bottom truss which did work and was a bit cheaper that of a bridge with a top and bottom truss. In my personal opinion I prefer the top and bottom truss bridge, although more complicated I found it to be less challenging to make and might give more strength on the actual model. With a bit more experimenting I came to the conclusion to use only hollow bars because they are cheaper and always stronger, the reasoning was explain be a TA that it is because it has a higher moment of inertia and thus will hold more weight. Also that when the bridge is is arched the weight wwill be distributed better and thus arch trusses can suport more weight.

WPBD is a very useful tool to make bridge design and test tension and compression. However I do not like using it for a model for the K’NEX competition. The K’NEX will not be joined perfectly like on WPBD also the K’NEX are all solid made of the same material and can’t be thickened so the fact that these can be changed and the goal in WPBD is to make the cheapest bridge not cost to strength ratio. If the bridge in the model is made solid, out of the same material, and same thickness then this can be more useful but they way it is being used is not very accurate for this assignment.  Two other problems with WPBD are there are no other forces, such as wind or age and rust; WPBD is only for the ideal conditions. The second is that the load added is fix, the weight added is limited to the one truck, which tell if it held or fell and the tension each piece was at, if more weight could be added and to a fixed location it would actually provide a defined weight limit and the cost of the bridge which would give a ratio used in our competition. WPBD is a very nice tool to make designs and see if there geometrically stable but not great when some conditions are fixed and real life is not ideal.

Next week we will use the knowledge gained by the guest speaker and use that to help with the next bridge design. We will also try a final analysis using WPBD before we start building the K’NEX model based on all the information gathered.

         - Kyle Hayes