Proctoring

[baker]

Boy, did this block deal separate those that read the rules and those who thought they did.... 1/3 of the teams were tier 3. Most of the tier 3 bridges were too short.

[Unome]

Boy, did this block deal separate those that read the rules and those who thought they did.... 1/3 of the teams were tier 3. Most of the tier 3 bridges were too short.

Same thing happened at Chattahoochee's invitational; I recall maybe one tier 2 and many tier 3's.

[Schrodingerscat]

I helped at a tournament this weekend, and I thought I'd share two rules of thumb we used that might help others:

1. A few bridges bended A LOT to the point that you couldn't visually tell whether it was touching the table within the clear span area. We made the judgment by sliding a strip of paper under the bridge inside the clear span area.
2. Since a load block is also 2cm thick, a spare one can be used to eyeball the 2cm rule. I believe we gave teams a little bit of leeway on this, but competitors: as said earlier, risk of tier 3 is almost never worth the gain of pushing margins.

Finally, in terms of problems we saw with competitors' bridges: quite a few were too short to span the entire length, a couple were designed assuming that the test support were wider than 5cm, and we required a few bridges to be loaded closer to the center than for which had been designed.

[dholdgreve]

I helped at a tournament this weekend, and I thought I'd share two rules of thumb we used that might help others:

1. A few bridges bended A LOT to the point that you couldn't visually tell whether it was touching the table within the clear span area. We made the judgment by sliding a strip of paper under the bridge inside the clear span area.
2. Since a load block is also 2cm thick, a spare one can be used to eyeball the 2cm rule. I believe we gave teams a little bit of leeway on this, but competitors: as said earlier, risk of tier 3 is almost never worth the gain of pushing margins.

Finally, in terms of problems we saw with competitors' bridges: quite a few were too short to span the entire length, a couple were designed assuming that the test support were wider than 5cm, and we required a few bridges to be loaded closer to the center than for which had been designed.

All great points, Mr. Cat!
A couple of additional thoughts:
There is no need to put your bottom chords all the way down at the bottom of the "rafters" and risk them touching inside the clear span area, or rubbing on the edge of the 5 CM block... Raise them up a bit (no more than 1/4") and be safe.
Regarding the 2 CM rule, yes we use the small side of a spare loading block as well... works great.
Nothing in the rules says the 5 CM block needs to set right on the bearing zone line. If your bridge is just a hair longer than needed, and you run into trouble with the 2 CM rule at the one end, you can move the 5 CM block back off the line and scoot the low end right up to the line to try to get under the 2 CM height restriction.
If you re using an automatic loader, DO NOT push the bucket around, back and forth, left and right, to try to keep the sand loading evenly... KEEP THE CHAIN PERFECTLY VERTICAL! It does not matter if the bucket tilts a little so long as the chain stays vertical. Pushing the bucket side to side to try to load the sand evenly causes the chain (and eyebolt... and loading block) to shift the load from one side to the other. This will cause the bridge to fail early.
That being said, make sure that when you hang the bucket, you hang it high enough that it will allow the bucket to tip a little and not contact the floor, even if the bridge deflects a little ... plan ahead.
If using an automatic loader, start slowly, allowing the bucket to tip whichever direction it needs to, but then quickly build to "wide open"(not immediately, but over the course of 10 seconds or so) Many bridges will only carry a load for a specified time... Get as much sand in the bucket as you can within that time period.
Read the rules... and build to them... I hate to see teams that have spent hours building a bridge, only to be tiered down due to a construction violation.
Finally, respect your build... The rules specifically say that once checked in, the bridge cannot go back into storage. You are to patiently wait for your turn to test I was amazed at how many kids I saw twirling the bridge, holding one end while tapping the other end on their other hand, chair, or partner. Cyanacrylate glue will dry very brittle... It is unforgiving. Handle this the way you'd handle Grandma's good China! Any jarring or sudden shock may cause the glue joint to crack before it is even tested. Also FWIW, this is a very easy "tell" in determining if the bridge was truly built by the team member... Competitive bridges take from 2 to 5 hours to build, depending on the design... Even the most inexperienced builders respect the bridge much more when they build it... If a team is disrespecting a bridge, it is highly likely that student did not build it.