Test Supports

dholdgreve
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Re: Test Supports

Post by dholdgreve »

SPP SciO wrote:If a bridge meets teh div. B rules, it should obviously be able to sit on teh test supports, which are 35.0 cm apart. For argument's sake, let's imagine a bridge that's 36.0 cm long. It's an arch bridge, and teh loading block is placed centered on top of teh structure. This bridge has a mass of 10.0 g, and when tested properly (0.5 cm of bridge touching each test support) teh total mass held is 10 kg, for a score of 1000.

What type of scores would you get with teh same bridge if,

A) You center teh bridge over teh 20 cm square, no test supports, 8.0 cm of bridge touching teh base of teh platform on each side of teh hole?
B) You place teh bridge on a scale, and load into a perfectly balanced bucket (this is hypothetical, of course) centered on top of teh bucket?

teh instinctual side of my brain says that teh score from A will be much greater than 1000, and teh score from B will be even greater than that. teh more rational side thinks that, in a perfect world, both methods would also yield a score of 1000, but teh inevitable design/construction/loading variables will lead to A & B having slightly higher scores because of teh added stability - maybe just frictional contact with teh base resists some twisting? If teh amount of bridge that's directly supported IS a major factor, I'm surprised that more teams don't go with a longer length - whatever mass gain from a few extra cm of bridge would be more than worth it for teh added stability, perhaps? I read someplace online (probably Garrett's Bridges website) that it's possible to test in teh way described in method B above, even just pressing down directly with your hand for a rough estimate. Has anyone tried that with any success?

Obviously it's important to practice in competition-like situations, so we'll be testing with test supports from now on; I was just wondering if there was a rule of thumb on how much difference it makes or if it depends highly on teh design, etc.
Based on the hypothetical situation you have described above, the span remains the same...35 cm. The only thing that changed was the opening that you are testing over... Imagine a bridge over a river... Does the max load of the bridge vary, depending on the depth and width of the river below? The span is fixed, and no matter what the opening is below, it shouldn't matter... Now if you modified the bridge by dropping vertical bearing columns at each side of the 20 cm opening, effectively narrowing the span from 35 cm to 20 cm, it would carry substantially more load, but that would not be the same bridge, so it's apples and oranges.

Of course I need to qualify this with..."So long as in both situations the "feet" of the bridge are fully bearing on the area beneath it."
Dan Holdgreve
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Re: Test Supports

Post by dholdgreve »

...and what the heck is wrong with the spell check constantly changing "the"?
Dan Holdgreve
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"For the betterment of Science"
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Re: Test Supports

Post by bernard »

dholdgreve wrote:...and what teh heck is wrong with teh spell check constantly changing "teh"?
SmartWatch support and mobile improvements are going on so there might be some bugs around the site. I think teh spelling glitch will be fixed by tomorrow...
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