The 13 th Annual Strongsville Truss Structure Competition indianalandmarks.org

The Basics You will work in groups of 1  3 students to build TWO balsa wood bridges. –If you chose to work in a group you must work with someone taking regular physics. –you will have the option after you build and test the first bridge to leave your group. You will not be permitted to change groups, but you can leave your group and go solo. You will RESEARCH the concepts of stress and strain as well as different bridge/truss styles. This research will help you to design and build a (hopefully) strong/efficient structure that is made of an inherently weak material. Your teacher will eventually break your bridges

Why 2 bridges? You will learn SO MUCH about the bridges (and stress and strain) when you see them break. We want you to actually learn from this experience and improve upon what you have already done (with bridge 1)

But, what if I’m awesome…and can’t improve? First of all…you can improve! But, we have a plan for that. –If your first bridge is truly awesome you can opt out of the second bridge… Check the rules sheet.

The Basics Yes…we said TWO (2) Bridges. Bridge 1 – Due February 21 –Must submit diagrams (see rules sheet) –Must meet all required dimensions –Must hold a minimum of 12.5 pounds –Will be graded based on 3 things: (1) met specifications and diagrams (2) held minimum weight (3) efficiency ratio* »See rules sheet for details

Bridge 1 - rubric GRADING Bridge 1 Tier 1Tier 2Tier 3Tier 4Tier 5 Specifications met? Yes = 15 / 15 No* = maximum points available 10/15 (but could be lower – depending on violations) *still “ testable ” Yes = 15 / 15No = maximum points available 10/15 (but could be lower – depending on violations) *still “ testable ” No and NOT testable. Non-Droppable Zero! Minimum weight held Yes = 7.5 / 7.5 NO = 0 / 7.5 NOT testable. Non-Droppable Zero! EfficiencySee Ratio Scale for your points. Maximum points available are 7.5/7.5 NOT testable. Non-Droppable Zero! Maximum score available CAN earn up to 30/ 30 points CAN earn up to 25/30 points CAN earn up to 22.5/30 points CAN earn up to 17.5/30 points Non-Droppable Zero!

What’s this “ratio” thing about? Your bridges will be judged on a ratio of how strong they are to how heavy they are. It would be very easy to build a very heavy bridge that can hold a lot of weight….that’s not the goal. You want a high ratio of weight held to weight of bridge. You want to build an efficient bridge…light but strong!

What’s this “ratio” thing about? Efficiency Ratio = weight held (Lbs) x 456 (grams/Lb) Mass of structure (grams) We have to convert to a common unit.

The Basics Yes…we said TWO (2) Bridges. Bridge 2 – Due April 9, 2013 Must submit updated diagrams (see rules sheet) –Must meet all required dimensions –Must hold a minimum of 22.5 pounds –Will be graded based on 5 things: (1) met specifications (2) modifications to original design (3) minimum weight held (4) efficiency ratio »See rules sheet for details HEADS UP…this is VERY EARLY in 4th quarter!

Bridge 2 - Rubric

The Dimensions You have some room to design as you like, but you are limited in the dimensions a bit. base = span = exactly cm Top must be between and cm Minimum Total height = cm Max below roadway = 7.00 cm In addition….your bridge MUST BE cm wide (outside to outside) at all points and can be no more than 80.00grams.

More details… To test/break your bridge we will insert a wood block into the side of the bridge. You MUST leave an opening in the side(s) of your bridge so that the block fits! Testing Block Length of block (9.8-cm) – this goes ACROSS the width (10.00cm) of your bridge Height of block Width of block Length of testing block = 9.8-cm (careful this is narrower than the bridge) Height of testing block = 3.1-cm Width of testing block= 6.3-cm

Even more details… To test your bridge you will place it between two lab tables as shown below. Two meter- sticks will be stacked up and clamped to the table to give your bridge something to push against (anchor it) 1 inch 1 1/8 inches 7/8 inch span = cm Your “roadway” must be “level” with the table. No higher than 1.0- inch Remember that you also have the option to build underneath the roadway. Max = 7.0-cm

One more thing… What do you build this out of? ¼ inch thick BALSA wood Or thinner! You can buy the planks or the sticks…it doesn’t matter to me (but it will matter in $$$) Make sure that you buy BALSA wood, not BASS wood. Any one-part glue. Be careful with the glue…some glues are really heavy.

What? Here…let us show you…. PLEASE NOTE… The bridges in this show were tested using the honors testing block. Regular physics students need to be aware that their bridges will be tested with a smaller rectangular block. However, the regular testing block will also be placed on the road way in the center of the span. When constructing your bridge, pay attention to where the block will be placed.

Length = 60 cm You can build beneath the road/deck of the bridge, but make sure that it fits! The Testing Set Up Honors testing block!

The Testing Set Up Again, this is the honors testing block! Pay attention to the dimensions of the testing block – if it doesn’t fit IN the bridge, the bridge cannot be tested! Length = 60 cm

The other side of this bridge was open; allowing the block to slide in from just one side. Good Idea or Bad Idea? Length = 60 cm

This bridge was made using I- beams. You can NOT use I-beams!

Length = 60 cm 7-cm under “roadway”

Remember… Your design must allow for the bus to travel down the length of the bridge as well as the testing block to fit across the center of the bridge. If the bridge does not have a clear passage way, points will be deducted. This bridge DOES allow for passage down the bridge.

These designs do NOT allow for travel down the bridge. This bridge DOES NOT allow for passage down the bridge. They blocked off the ends!

You are NOT permitted to place the testing block on TOP of the structure. This is NOT a LEGAL test  This resulted in a non-droppable zero! The testing block must go on the “roadway” which can be no higher than 1-inch above the table top.

Don’t get too attached….

Legal Truss Systems The following are common truss systems. You may use variations of the following: King Truss Warren Truss Pratt Truss Lattice Truss Whipple Truss You cannot just build a box (“box truss”) – that is NOT the intension of the project and will earn you a non-droppable zero! Hint…LOOK online and around the real world at some bridges. Don’t try and come up with something new…adapt what’s already out there to fit the needs for this project.

Legal Joints Single overlapping joint 1in

Legal Joints Double overlapping joint 1in

You are NOT permitted to “stack” joints. You may NOT stack/overlap more than 4 pieces! You may have a double overlap with UP TO 4 pieces. This IS legal as long as the overlap is within the ½ inch allowance! This IS NOT legal! You may not “stack” the beams!

Legal Joints Butt joint This is when two pieces of wood are “butted” up against each other (end to end) 1in

Legal Joints Gusset Plate This is a SMALL square of wood that protects the joint underneath. This can be placed over any of the (legal) joints mentioned. NOTE THE DIMENSIONS! Gusset Plate no bigger than 1-in 2

You are NOT permitted to “stack” joints. This is a legal gusset joint This is NOT legal! This is two butt-joints protected by a gusset plate.

Good joints! Gusset plate Pieces are notched so they fit snugly. This is strong as long as you don’t cut through too much of the board.

NO I-Beams I-beams are NOT permitted!

NO H-Beams H-beams are NOT permitted and they are dumb.

NO Lamination! Lamination is the stacking of pieces of balsa wood as shown below. THIS IS NOT PERMITTED! 1/4” or less You must be very careful with your joints. If you have too much area overlapping it will be considered lamination.

All members must be structural in nature. You can NOT add members just to meet the requirements! Something like this will result in a disqualification! Come on…really?

You ARE permitted to measure the dimensions of the desk edge and build your structure so that it fits the gap. Note – the meterstick will be placed 1.0-cm away from the edge of the table.

Building Tips Choose your wood wisely! –Make sure that you purchase BALSA wood! –Choose wood that is straight and dry! –Balsa is inherently weak, but try to choose pieces with few flaws Cut your pieces with a sharp X-acto ® knife OR use a miter box and small craft saw. Give yourself PLENTY of time to build! Create actual size “building plans” that will allow you to easily put your members together. Put a piece of wax paper over the plans then place objects directly over top to ensure that all pieces are cut to the appropriate size and glued in the correct manner. The wax paper keeps the glue from sticking to your actual plans.

Important Information Bridge 1 Due on February 21, 2013 You must have your plans (printed) and bridge in class and ready to impound. NO LATE BRIDGES WILL BE ACCEPTED! Bridge 2 Due on April 9, 2013 You must have your adapted plans and bridge in class and ready to impound and test Testing will begin in class on Monday! NO LATE BRIDGES WILL BE ACCEPTED!

Internet Resources This site will help you design your bridge. It also has links to sites that will “calculate” how your bridge will perform. This site has a link to download the West Point bridge design software. There is a LOT of information on the web for this stuff…remember this is a RESEARCH PROJECT so do some RESEARCH!

Good Luck!