BRIDGE RULES AND GRADING CRITERIA
Due WEDNESDAY, May 11, 2011!
BEFORE STARTING TO BUILD:
Look up bridges on the Internet. That’s bridges in general, as well as toothpick bridges. You might also do a search for engineering, designing structures, and so on. There will probably be a big competition again next year using West Point Bridge Designer software. The winning high school students will receive $15,000 in scholarships; some of the winners from a few years ago went to Tuscaloosa Academy! Check out the details: http://bridgecontest.usma.edu/download.htm or google West Point Bridge Designer. Also read Ch. 18 in your textbook. We usually do this as a class, but weather days out have been too numerous.
A. Materials
1. You must use ONLY wooden toothpicks and glue. NO EXCEPTIONS!
2. These must be normal toothpicks, not long craft sticks, popsicle sticks, etc. Try NOT to use the flat, thin toothpicks as they are flimsy and NOT strong enough to build good bridges.
3. There is no maximum OR minimum number of toothpicks you may use. However, remember that the object is to make the bridge as STRONG And LIGHT as possible (that is efficiency). Don't put in any toothpicks unless they make the bridge stronger and able to hold more weight.
4. You should use wood glue (or carpenter's glue). You can find it at any Wal Mart, Hardware store, usually even at drug stores and grocery stores.
5. I highly advise that you sit the whole thing on wax paper, so it will be easier to unstick it if some of your glue drips.
B. Design--Bridge Dimensions
1. You must have a preliminary design drawn within 1 week. I will check your design in class. (WITH DIMENSIONS) (Due to storms, you need to show me a design by Friday, May 6th if you choose to build a bridge!)
2. You do not have to STICK to that exact design, as you may choose to adapt it as you go along.
3. The MINIMUM LENGTH IS 50 CM. You will be counted off if you do not meet this minimum. I highly advise you not to go too much over that length, as it will just add weight and NOT strength. Try to make your bridge 50 cm long. MEASURE as you go with a METRIC ruler.
4. The twp tables will be set apart 30 cm, and your bridge will cross this span.
5. The MINIMUM WIDTH is 5 CM. (This is about the same as the length of one toothpick.)
6. There is NO HEIGHT OR DEPTH RESTRICTION. Make it as high as you need to in order to maximize the strength.
7. There MUST be a place for the BLOCK (2 x 3 x 5 cm) to sit on your bridge! The block is what holds the hook where we will suspend a bucket and add weights until your bridge collapses. You MAY have your OWN block if you like.
C. Other Design Rules:
1. You may NOT glue two toothpicks right together longways along the whole length of the toothpick. They may not overlap longways more than 1cm. There MUST be substantial light that can be seen between ANY and ALL of your toothpicks. You must have every two toothpicks separated by space or by another toothpick going another direction (like stacking logs in a log cabin). May overlap 1 cm!
2. You DO NEED to have crosses, as triangles are the strongest static (not moving) shape. (LOOK UP TRUSSES ON THE INTERNET!) However, the ANGLES between your crosses should be at least 45 degrees. In other words, you cannot use such small angles that you might as well have glued your toothpicks together longways.
3. You must have a ROADBED, or a flat plane on your bridge which a car could cross if it were used as a real bridge. (Skeleton foundation or frame of a road bed. No solid surface.) Could a toy car get from one table to the other using my bridge? In other words, you cannot just clump a bunch of toothpicks together in a glob. ;-)
Grade
1. This is a 150 point grade. It is broken into two 50 point grades, a 15 point grade for using West Point Bridge Designer (and turning in printout of plan), a 20 point grade for data and analysis sheets, and a 15 point participation grade for being involved and helping with the bridge competition.
2. The first 50 POINTS is based on:
a) Did you turn it in on time (or early!)? Your grade will drop 10 points for EACH day the bridge is late, REGARDLESS of the reason. You have AT LEAST TWO WEEKS to get this bridge built and turned in, and you may turn it in early, anytime you like.
b) Did you follow all the rules? Points will be taken off for any rule not adhered to.
c) How much time and effort did you put into the bridge? This is subjective, and depends on my opinion of your bridge.
3. The second 50 POINT grade is based solely on EFFICIENCY.
a) EFFICIENCY = LOAD HELD / BRIDGE MASS
b) This means you add up everything the bridge holds--the block, hook, bucket, and weights. That is the LOAD it holds. Then you divide that by the MASS of your bridge alone. This is your efficiency score.
c) Your bridge's efficiency will be RANKED with the rest of the bridges in your class. The most efficient bridge gets 50/50. The least efficient bridge usually gets 25/50 to 30/50, depending on the class.
4. The last 50 POINT grade is based on:
a) Participation: You must PARTICIPATE in the bridge activity, helping measure, count, clean up, write on the board, whatever needs doing. You must also test your own bridge, and help out while others are testing their bridges.
15 POINTS
b) Using West Point Bridge Designer, and turning in a printout with your bridge plan along with the analysis sheets which I will give you when we start TESTING bridges. (This includes appropriate behavior in the library using computers.) We will do this in the computer lab, but you may FIND IT HELPFUL TO DOWNLOAD THE PROGRAM FOR FREE ON YOUR HOME COMPUTER FROM
http://bridgecontest.usma.edu/downld2002.htm
15 POINTS
c) You must also turn in the analysis form (which I will give you when we start TESTING bridges) with all your bridge dimensions, as well as your bridge's mass, efficiency, etc. You must also sketch your bridge on this form IF it is different from your West Point printout.
In addition, on this form, you must analyze your bridge and tell me all the PHYSICS that went into the planning and testing of your bridge: FORCE, TENSION, NET FORCE, INERTIA, GRAVITY, WEIGHT, MASS, PRESSURE, SHAPES, FORM & FUNCTION, etc., etc. I WILL GIVE YOU THIS FORM. You must include what you would do differently if you built a structure like this again.
20 POINTS
5. THIS ADDS UP TO 150 TOTAL POINTS! (50 + 50 + 50) ;-)
GOOD LUCK, AND HAVE FUN DOING THIS!!!! Although each person must do their OWN bridge, it will probably be more fun if two or three people build their bridges TOGETHER in somebody's carport, etc.