In the last week we designed our bridge for initial testing in lab this week. We all designed our own bridge and worked off the one that held the most weight (around 33 pounds). We modified the middle of the bridge to hold more weight, adding a couple more members and gussets, since that is the area the bridge failed when we tested it. Adding up all the parts resulted in a total of $133,000, which is a bit more expensive than our initial design, but hopefully more stable. This week when testing the bridge we will be filling the bucket with sand, a more uniform weight distribution, allowing for equal stress to be placed on more members instead of more weight on less members and gussets.
Our bridge design did not change much compared to our designs last week, so we can't really address that question. However, in response to the other question, designing a K'Nex bridge spanning two feet is a lot different than spanning a steel bridge spanning twenty for a couple reasons. First of all, a K'Nex bridge experiences the most weight and stress on the gussets, since a K'Nex member is relatively strong. Steel bridges, depending on the strength of the welds and members, will be more inclined to have stress throughout the bridge. This is actually a reason why designing these K'Nex bridges are more difficult, because more emphasis needs to be placed on the gussets. Another difference is steel is, of course, a much, much stronger material the K'Nex, allowing it to hold more weight, but then again, no cars are going to be driving over a K'Nex bridge anytime soon. Since steel is also stronger, less material can be used for a given area in the bridge, probably resulting in a better cost to strength ratio.
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