The scoring system for any event should be designed to reward the preferred outcome. In developing an event, you have to start out be deciding what the event is about, what you hope to have the kids take away from it, which details contribute to the outcome that you intended.
To me, this event and the other structure events are about the students exploring the limits of all aspects structures, including design, material selection, craftsmanship, and - as evidenced by this board - development of a body of knowledge and collaboration on research. It is limited by the choice of simple materials, to insure broad participation, and by practical limits on staging a tournament, such as the choice of sand and the maximum available load of 15 kg. The take-away here is that those students who really work at this event will have a good understanding of how and why structures do what they do, an understanding that will come through repeated, destructive testing of structures.
There is no significance to holding 15 kg of total load. It is not a design load. Nor is there any significance to holding 10 kg, 5 kg, or 1 kg. Load is load, and what matters is how the structure being tested responds to the load. The 15 kg of load written into this event is a practical limit on what the supervisor is expected to provide. It forces students to build light. Ideally all the structures would be loaded to failure to determine their efficiency and ultimate strength, but no tournament can be expected to provide an open-ended amount of sand. By cutting off the available load, heavy structures with high capacity are self-defeating because they can't utilize their all strength to increase their score. Therefore, students must learn to use minimal resources. Saying that structures must "carry all the load" is a fundamental misunderstanding of the event.
Many years ago, I coached my daughter's Odyssey of the Mind team in a simple tower building problem. She built an 8" tall tower, legs straight up, which weighed 15 grams. The team stacked barbell weights on it, it broke at 960 lbs. We went on to state tournament and got beat by a team carrying 1000 lb. I don't think we need to stage events with massive amounts of weights to load destructively, by allowing structures to score their efficiency at failure with limited maximum load and encouraging team to build light, we accomplish the same thing.
The argument that these structures ought to "carry all the load", because, after all, who wants to be on a structure which collapses - we might be killed - and no good engineer would allow that to happen, is a tired old argument which is not valid in this context. How do you suppose that engineers know how to build safe structures? Maybe it's because someone did the research to learn how structures fail and or they succeed, and how they can best be built with a given set or resources. I think that's what we're doing in this event, we're learning what it takes to make good structures. It's the sort of knowledge that practicing engineers apply to make those real world structures.
In 2004 Towers were required to carry all 15 kg to be in the first tier. At Nationals (in Juniata) the 31st place tower weighed 290 grams and had an efficiency of 52, but it was first tier. The 32nd place tower wieghed 6.46 grams and had an efficiency of 2217. Do you believe that the team that worked harder and learned more was rewarded? Really?
If these structures were actually being judged by the standards of real-world structures, they would be judged with a safety factor of five or more, they would be evaluated for capital cost, serviceablility, longevity, life-cycle costing, aesthetics, and effectiveness at addressing the intended function, whether that is to support traffic, house people, carry power lines, etc. In terms of efficiency, capital cost is likely to be the closest measure, and that depends more on availibility of materials, market conditions, availability of skilled trades to work the materials, suitability of the materials to the climate and specific conditions of the site, and so on. These real world structures would never -that's NEVER - be judged on a measure of load-held vs structure mass.
Structures built for S.O. are not life-preserving structures, and real structures are complex to accurately model or score. These are learning tools, research structures. I am astounded by the amount of information and wisdom shared by the members of this board. I think we've managed to model collaborative research. I wouldn't have it any other way.
Grand haven, MI