2015 Competition Guide
Every year we see some pretty common design errors that we'd like to warn you about but, before we go too far, we need to warn you that this is FREE advise and might be worth what you pay for it. There is no substitute for THINKING about what you are doing in light of all that great training that you've been receiving in your engineering courses. Statics really is true as are the concepts learned in your structural mechanics, structural analysis, and materials courses. One of the great objectives of this competition is to help you connect what you learn in class with real life.
This year there are some substantial changes in the rules regarding connections. You will want to review the "Post Construction" page for more details on this.
So, that said, here are the tips.
Scoring is based on three parameters: Lightness, Stiffness, and Speed. These are combined to determine Economy, Efficiency, and ultimately Overall Cost. Before getting too deep into your design you should run some scenarios to decide which is the critical parameter. Knowing this will have a big effect on which way you go with your design.
One way to do this easily is to download the scoring spreadsheet and create entries for your various designs. You will need to estimate things such as weight, time of construction, and stiffness and compare the resulting scores. By the way, if you do this and find an error in spreadsheet PLEASE report it ASAP so that the spreadsheet can be updated.
Every year teams lose out on great rewards by a matter of a sixteenth of an inch or less. One year an apparent national champ lost out because the penalty associated with their base plate extending a sixteenth of a inch outside the footing knocked them out of the top ten. That REALLY hurt. It wasn't fun for the judges either.
Teams often push the clearance limits and then something happens during construction so that things don't line up too well and a big penalty is assessed. It is STRONGLY recommended that you think twice (or more) before you commit to building a bridge that is intended to precisely meet the spatial limits. It generally won't hurt your overall performance to leave a quarter inch or so to spare.
The Rules Committee comes under pressure regularly from competitors and sponsors to outlaw expensive steels, such a Chromalloy because there is a perception that somehow these steels give an unfair advantage to chapters with money to spend. When the rules committee can find a way to outlaw such material that is enforceable we probably will. Writing an enforceable rule restricting the type of steel has proven to be difficult.
These expensive steels seem to be used primarily because they can be obtained in lighter sections. They have generally the same stiffness (i.e. same Modulus of Elasticity, E) as other steels so they don't have a real impact on stiffness. In fact going to lighter sections may have a detrimental impact on stiffness (because of reduced AE or EI). They do come in higher tensile strengths than some of the other steels however the strength levels required by most members is minimal so there's not a huge savings here either. You might also note that if member strength is based on buckling then tensile strength is a non-issue and higher strength steels have no advantage over lower strength steels in this case. In the end, we find some very competitive bridges at the national competition that do not use these steels.
With all this in mind, the Rules Committee issued the following suggestion in August 2006:
Buying Steel Economically
Each year the rules are modified by the rules committee. Frequently we encounter teams which have not pick up on nuances of changes found in the current year's rules and acquire significant penalties. Careful attention should be paid to this year's rules.