Elevated Bridge B/C

[jazzy009]

thats what i figured. its mostly superstition

[geraldatwork]

For the most part event judges have become wise to the wood drying tricks. Students used to get a few tenths off the devices using a hair dryer then quickly rush to submit the bridges or whatever to impound where they would be weighted. By the next day or a few hours later they would retain the moisture. Now it seems in most cases the devices are "officially" weighed just prior to testing.

[dholdgreve]

But without an impound, like this year, it's still possible to dry it down then rush it to the check in station!

Several years ago, at the Ohio State competition, there were two bridges that were were weighed to the .01 grams, then tested. The two bridges weighed EXACTLY the same, to the 1/100 of a gram, and both carried the full load... There was actually a tie for first place! Both bridges were re-weighed after being tested, and one had gained back .03 grams because it had been artificially dried down just before impound, while the other remained constant. Sometimes it can work against you!

[dholdgreve]

If you do plan on drying the bridge down, I think the most effective method would be to place the bridge in a box slightly larger than the bridge, cut a 1-1/2" diameter hole in the one end, then insert the business end of a hair dryer in it and plud it in. The hot, dry air can take up to .5 grams off a bridge on a humid day! (For a very short time)

[geraldatwork]

But without an impound, like this year, it's still possible to dry it down then rush it to the check in station!

Several years ago, at the Ohio State competition, there were two bridges that were were weighed to the .01 grams, then tested. The two bridges weighed EXACTLY the same, to the 1/100 of a gram, and both carried the full load... There was actually a tie for first place! Both bridges were re-weighed after being tested, and one had gained back .03 grams because it had been artificially dried down just before impound, while the other remained constant. Sometimes it can work against you!

I would think that drying wood makes it more brittle and easier to snap under load if it was dried just prior to testing and didn't have a chance to rehydrate. Think of when you want to have curved wood in a bridge. You put it in the tub it absorbs water and you can bend it without breaking. Or tree limbs in the forest, newer "green" wood is hard to break where older dry limbs snap easily. In your example above, both bridges held all of the weight and the one that was dried won. However if you accept the fact that dry wood is more brittle and more likely to snap, the bridge that won was probably over built to hold the 15kg and could of come in lighter. In reality both bridges may have been over built.

[gandhiji]

well i just tested my bridge that weighed 11.2 grams and it held 8.9 kg, for an efficiency of 790...do u think that would be good enough for a medal in a small state like delaware???

[dholdgreve]

But without an impound, like this year, it's still possible to dry it down then rush it to the check in station!

Several years ago, at the Ohio State competition, there were two bridges that were were weighed to the .01 grams, then tested. The two bridges weighed EXACTLY the same, to the 1/100 of a gram, and both carried the full load... There was actually a tie for first place! Both bridges were re-weighed after being tested, and one had gained back .03 grams because it had been artificially dried down just before impound, while the other remained constant. Sometimes it can work against you!

I would think that drying wood makes it more brittle and easier to snap under load if it was dried just prior to testing and didn't have a chance to rehydrate. Think of when you want to have curved wood in a bridge. You put it in the tub it absorbs water and you can bend it without breaking. Or tree limbs in the forest, newer "green" wood is hard to break where older dry limbs snap easily. In your example above, both bridges held all of the weight and the one that was dried won. However if you accept the fact that dry wood is more brittle and more likely to snap, the bridge that won was probably over built to hold the 15kg and could of come in lighter. In reality both bridges may have been over built.

Actually, the one that was dried was the one that gained the weight back. The one that was at its equilibrium was the winner, as it didn't gain any. That was the year that a Tier 1 placement REQUIRED that all 15 Kg be held for 5 seconds, so neither were substantially overbuilt... I think both weighed 6.03 grams when the competition began, if I remember correctly. As for green wood versus dry wood, I'm not sure I can agree with your assumptions... I'll buy that dry wood is more brittle than green wood, but it also way lighter! As far as straight out compressive forces, I think alight weight, dry, brittle piece will provide a higher efficiency than heavy, wet, green piece Any other thoughts on this one?

[croman74]

well i just tested my bridge that weighed 11.2 grams and it held 8.9 kg, for an efficiency of 790...do u think that would be good enough for a medal in a small state like delaware???

From scores posted on this site that people have had, for regionals you could probably win. For states, you might be able to sneak in a medal.

[bob3443]

well i just tested my bridge that weighed 11.2 grams and it held 8.9 kg, for an efficiency of 790...do u think that would be good enough for a medal in a small state like delaware???

i got a bronze medal in NJ state's with an efficiency of 770.

[Dark Sabre]

What are you building your test bases with?

I spent the better part of an hour looking around Lowes for nice solid and flat pieces of wood, but wasn't terribly happy with what I ended up with :\
(judging a regional Saturday)