Test Supports

abox
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Re: Test Supports

Post by abox »

Could someone just post a diagram of the test supports and lines? Much appreciated ;)
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Re: Test Supports

Post by retired1 »

You are making this far more difficult than it is.
You have a platform with a specific sized hole in it. It has a center line for the hole-Front to rear. This has 2 parallel lines at a specified distance for B or for C.
Next you have 2 blocks of a specified size that have the inside portion touching the respective line to give the required distance between the support blocks.
Your bridge simply sets on top of the 2 blocks. The blocks are not part of the bridge, they are part of the test stand.
If in doubt, draw your own picture based on the rules and it will become readily apparent.
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Re: Test Supports

Post by skyman »

I made this quick Sketchup Model of the testing apparatus. I believe everything is correct, but comment if anything seems incorrect. In my model I drew the 15 cm edges of the Test Supports perpendicular to the center line. Are we allowed to rotate the Test Supports so that the 15 cm edges are parallel to the center line?
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Re: Test Supports

Post by sjwon3789 »

@skyman is that correct? Im still confused w/ the rules with test supports. Before I saw that, I interpreted the rule as the bridge having a length of 45cm, with test supports being apart by 39cm (since each of them are 3cm). Looking under rule 3.b., it says the test supports will be at either end of the bridge. So wouldn't this mean the test supports can be however long, like 39cm, or longer?

If the diagram that skyman drew is correct, would that mean the optimal length of the bridge would be 51cm? Since it would lie on the test support as much as possible. My friend is saying it should be like 45.5cm so I'm getting really confused.

When the rule says "the bridge must span an opening of 45cm," is that saying it should be a length of 45cm, or greater than 45cm?


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Re: Test Supports

Post by chinesesushi »

sjwon3789 wrote:@skyman is that correct? Im still confused w/ the rules with test supports. Before I saw that, I interpreted the rule as the bridge having a length of 45cm, with test supports being apart by 39cm (since each of them are 3cm). Looking under rule 3.b., it says the test supports will be at either end of the bridge. So wouldn't this mean the test supports can be however long, like 39cm, or longer?

If the diagram that skyman drew is correct, would that mean the optimal length of the bridge would be 51cm? Since it would lie on the test support as much as possible. My friend is saying it should be like 45.5cm so I'm getting really confused.

When the rule says "the bridge must span an opening of 45cm," is that saying it should be a length of 45cm, or greater than 45cm?


Thanks!
Skyman's diagram is beautiful and correct.
As for your second question, the bridge does not have to lie across the entire width of the test support. Making it longer also makes it heavier, and depending on the design of your bridge, making it longer may have a negligible (or negative) effect on your efficiency score. Your friend is correct if your bridge allows for each side to only extend 0.25 cm on the test support because the shorter length allows for a lighter weight.
The opening is 45 cm, the bridge's length should obviously be slightly longer to be able to support itself. Like retired1 said, the rules are clear and you might be overcomplicating it. :mrgreen:
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Re: Test Supports

Post by SPP SciO »

How different would results be, if you tested your bridge across a 20x20 opening, without resting on the test supports? In other words, will the platform actually support some weight?

Looking at a google image search I can only infer that either, it hardly makes a difference, some event supervisors ignore the test support rule, or this is something new and most pics are >1year old - most bridges seem to be resting directly on a table.

Our team has tested pretty haphazardly; we haven't built and tested enough to be worrying about those details (construction techniques and designs pose enough of a challenge). Is this a major deal? Our div b bridges clear the span by about 0.5cm on each side but adding weight with that little surface area of contact seems awfully precarious. Hoping it's one of those things where physics trumps intuition.
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Re: Test Supports

Post by DoctaDave »

Testing across the 20x20 cm hole instead of the test supports makes a HUGE difference. The span is 4/7ths of what the B div rules state, meaning the mass of the bridge can effectively be cut down to 4/7ths of the original mass.
An ES cannot ignore the rules of the test supports. The whole point of bridge building is to design and build a structure that can support a load across a specified span, which is either 35 or 45 cm. It would defeat the purpose of the event to change the testing apparatus parameters given by the rules. Also, if the bridge doesn't span the given distance of 35 or 45 cm your team gets tiered, which means you get placed below all the teams that had no construction violations, and at this point in the season with only states and nationals, (and maybe a few more regionals?) left, getting tiered is basically getting last, or close to it at least.

In a nutshell, don't use the 20x20 cm hole to test, use the test supports.

Also the .5cm on each side should be enough to support the entire bridge on the test supports. If you've tested it so far with just .5 cm of overhang on the test supports and it hasn't yet failed, it should be fine in the future as well.
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Re: Test Supports

Post by bernard »

SPP SciO wrote:Looking at a google image search I can only infer that either, it hardly makes a difference, some event supervisors ignore the test support rule, or this is something new and most pics are >1year old - most bridges seem to be resting directly on a table.
If you look at the video on the Science Olympiad TV channel, for the first bridge shown, without the tests supports it would have a span of only 20cm. For older pictures/videos, you might be looking at Elevated Bridge, where test supports weren't necessary because of the rules.
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Re: Test Supports

Post by dholdgreve »

SPP SciO wrote:How different would results be, if you tested your bridge across a 20x20 opening, without resting on the test supports? In other words, will the platform actually support some weight?

Looking at a google image search I can only infer that either, it hardly makes a difference, some event supervisors ignore the test support rule, or this is something new and most pics are >1year old - most bridges seem to be resting directly on a table.

Our team has tested pretty haphazardly; we haven't built and tested enough to be worrying about those details (construction techniques and designs pose enough of a challenge). Is this a major deal? Our div b bridges clear the span by about 0.5cm on each side but adding weight with that little surface area of contact seems awfully precarious. Hoping it's one of those things where physics trumps intuition.
I think it depends on the design... If you have designed your bridge to span a 350 mm space, then place it over a 200 mm space, I doubt it makes any difference at all... especially if you are top chord bearing, where the load is being transferred directly down columns with ends bearing on platform.

If you have designed the bridge to span only the 200 mm opening, obviously the requirements are much less.
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Re: Test Supports

Post by SPP SciO »

If a bridge meets the div. B rules, it should obviously be able to sit on the 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 the loading block is placed centered on top of the structure. This bridge has a mass of 10.0 g, and when tested properly (0.5 cm of bridge touching each test support) the total mass held is 10 kg, for a score of 1000.

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

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

The instinctual side of my brain says that the score from A will be much greater than 1000, and the score from B will be even greater than that. The more rational side thinks that, in a perfect world, both methods would also yield a score of 1000, but the inevitable design/construction/loading variables will lead to A & B having slightly higher scores because of the added stability - maybe just frictional contact with the base resists some twisting? If the 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 the added stability, perhaps? I read someplace online (probably Garrett's Bridges website) that it's possible to test in the 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 the design, etc.
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