1. The problem is to design, construct and test the most efficient bridge within the specifications. Back to start of slide show

2. Efficiency The mass of the load (grams) The mass of the bridge (grams) E = Back to start of slide show

3. Materials The bridge may be constructed only from ¼” x ¼” balsawood and wood glue. The wood may be cut, notched, sanded or laminated. No other materials may be used. The bridge may not be painted or coated with any substance. The bridge will not weigh more than 30 grams. Back to start of slide show

4. Construction The bridge must span a gap of 300 mm. (S) The length of the bridge must not exceed 400 mm. (L) The height above the roadbed can not be greater than 150 mm. (H) The maximum width of the bridge will be 80 mm. (W) Back to start of slide show

5. Testing A 40 mm square loading plate will be centered on the roadbed and force will be applied from above. The load will be increased in increments until bridge failure is determined. Failure will be determined when the bridge will not support any more weight or when the bridge deflects 25mm below the load. The bridge with the highest structural efficiency, E, will be declared the winner. Back to start of slide show

6. Kinds of Joints Butt Joint- weakest joint Miter Joint- ends angled (mitered)-moderately strong joint. Lap Joints plain lap- weak edge or middle lap- moderate to strong joint Notched Joint (rabbit, dado, etc)- very strong Lamination- gluing layers together for strength Back to start of slide show

7. Use jigs (holding devices) to help hold or align pieces while gluing. The weight of each piece of wood can vary. Use denser wood in the roadbed. Brace horizontally and vertically to help prevent failure due to torsion. Allow time for glue to set before moving pieces. Use sandpaper to remove fuzz before gluing. Be careful not to round edges. Check for a good fit- avoid gaps and spaces in joints. Laminating may be a good idea. Wood has a critical length- the point at which it will crush rather than break. Each time you divide a piece of wood in half, it takes four times as much force to bend it. Back to start of slide show

8. Keep it simple, straight, level, smooth, well glued. Use quality workmanship throughout! Back to start of slide show