Bridge Div C question

[RandomStudent123]

Is there a maximum amount of weight they will put on your bridge? (Div. C)

[mklinger]

Is there a maximum amount of weight they will put on your bridge? (Div. C)

15kg is the maximum load your bridge will have to hold

[mnoga]

Usually, the amount of sand in the hopper is between 15.1 and 15.2 kg, or at least that is the recommended amount for the event. That ensures that if a little sand is left in the dispensing tube due to low flow, the bucket/sand/block/chain in total should end up weighing more than 15kg.

If your bridge is built to hold about 15.2 kg and it stays intact, then likely you can use it again at a future event and it will again hold above 15kg.

[pumptato-cat]

I'd be a bit careful on assuming whether the bridge will hold the same weight twice.
I pre-tested a bridge last year that held 15kg twice, and at states, it broke at 14.6kg. I'm not sure why that happened, but definitely don't assume your bridges will consistently perform.

[BobaTeaTastesGood]

Usually, the amount of sand in the hopper is between 15.1 and 15.2 kg, or at least that is the recommended amount for the event. That ensures that if a little sand is left in the dispensing tube due to low flow, the bucket/sand/block/chain in total should end up weighing more than 15kg.

If your bridge is built to hold about 15.2 kg and it stays intact, then likely you can use it again at a future event and it will again hold above 15kg.

How many times have you been able to successfully reuse bridges? I'd like to collect my own data, but all of our barely-above-15 bridges break during unloading etc.

I believe it's held that you shouldn't reuse bridges or bridge parts, and I've never reused old bridges in competition or anything like that. Usually I keep winning bridges as souvenirs/models lol. Is this a sound strategy (at least to keep a good, reused bridge as a backup)?

[kjlokesh]

This year non of our bridges broke (Div B) in the competition. Surprisingly it didn't break after we tested again at home. Bridges weight range from 4 to 4.5 grams. Our trail bridges broke consistently during practice (< 15kg) , weight ranges from 3.5g to 4g. I remember years back a team at Centerville invitational said they always test the build before competing.

If the build quality is good then you may use the bridge at least 2 runs.

[mklinger]

This year non of our bridges broke (Div B) in the competition. Surprisingly it didn't break after we tested again at home. Bridges weight range from 4 to 4.5 grams. Our trail bridges broke consistently during practice (< 15kg) , weight ranges from 3.5g to 4g. I remember years back a team at Centerville invitational said they always test the build before competing.

If the build quality is good then you may use the bridge at least 2 runs.

This can be a very complicated thing. My experience, in general, it depends on how close the device is to its maximum (eventual) failure load. If you are testing only to about 70% the failure load, it should be able to be used indefinitely. We've pre-tested devices over 10 times with this condition for example and even over the span of more than 1 year between tests. The closer you get to its ultimate breaking load, the more chance there is to do damage during the test. One technique is to try and listen very carefully during testing to see if you hear any creaking. That can be a sign of damage, although it's not a guarantee.

Also, remember, each test, especially if it's not one right after the other, will be set up slightly differently with the loading block not in the exact position it was before, so that may induce some difference between one test and another.

This is the main reason why the 5kg bonus for holding 15kg is a big challenge even for the very top builders. You have to decide if you want to guarantee holding 15kg by overdesigning, have a reasonable chance - maybe test to 11kg multiple times, or just take your chances and hope it holds everything like a previous build did. I talk about this in my 5900 Div B bridge building video a lot if you want to check it out: https://youtu.be/LI5n4PJFTCg

Good luck!!

Marc