We're continuing with truss bridges. This project needs more accurate taping, which might be a tad difficult for primary students. However, I've done this project with a group of 3rd graders, and they were able to build sufficient truss bridges.
Step 1: Gather Your Supplies
- A bag/box of straws
- Small cups
- Paper clips
- Weights – pennies, paper clips, etc. Anything is OK as long as they weigh the same. You want to compare how much different bridge designs can support
Step 2: Cut the Straws & Tape the Pieces Together
- Cut a bundle of pieces to same size (~2 1/2 inches long). Leave some for different lengths. These will be cut to size.
- Tape four pieces together to make a square. Tape uniformly across all places. Create enough square to span an opening that is 10 inches wide.
Step 3: Put the Sides Together
- Created bottom of the truss bridge first, then continued to build the sides of the bridge. (These squares measure to 11 inches in length.)
Step 4: Finish Your Truss Bridge
- After creating several squares, put cross bracings diagonally (cut these to size).
- Put the top pieces last and enclose the truss bridge.
Step 5: Test Your Bridge
- Place the truss bridge between two desks, tables, chairs, etc.
- Hang a small cup in the middle of the bridge (use hole puncher and paper clips) and load it with pennies, paper clips, etc. to weigh it down and test its strength.
Step 6: Failure & Improvements
- Different size straws, too much tape on one side, etc. will create imbalance and weaknesses in the bridge structure.
Remember, Engineering is all about failing and trying, again. So, try and try, again.
This bridge was very strong. I ran out of buckets and couldn't hang more to test how much more this bridge could support. But, my guess is that it would have supported another two or three mini-bucket full of coins.
Build your own today and test it for yourself.