It works because all the members are connected to that one joint, so it disperses the stress between all the members and stands. Every member is crucial though. If i remove any of them, the bridge will be unstable:
I changed the width of some of the members. It is completly symmetrical ,so the width of each member corresponds to the width of its reflection on the other side of the joint. The widths from right to left, go 120, 250, 220, 200, 180, 170, 170, 180, 200, 220, 250, 120 (all mm). The outside ones are further from the joint and therefor incur more stress so they must be wider. If I decrease the one that is 250, even just to 240, that member will collapse:
For each member I decrease, that member will collapse. And regardless of which one it is, it breaks the same way. Watch me change one of the inside ones to get the exact same result, just on a different member:
Since there are so few members, it makes each one all the more critical. The only other thing that can be changed is the members going across the top. These cannot go below 140 mm, but if they do:
Absolute failure occurs. So moral of the story is, thats each member works off the other members and if you change one, it has a big impact on the bridge. Each member plays its part, and if you do not want to wasteful, and be efficient like this bridge, make it so no member can be removed or made skinner.
The last thin there is to see is if i move the joint. If I move it to either side, the imbalance causes it to immediately collapse. If i move it down, there is more stress, because the members are longer, so they cannot handle it. If i move it up, the entire bridge just falls down. I will show you an image of when I move the joint up:
The total cost of the bridge that actually works is $400,000. and there is nothing that can be changed on this design to make it cheaper. Other designs may be cheaper, but this is at its ultimate low.
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