Monday, May 23, 2016

Bridge Building Series - Truss Bridge 2

Truss Bridge 2 – Straws & tape (A challenge project)

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.

Supplies:
·         A bag/box of straws
·         Tape
·         Scissors
·         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
    
Instructions:
1.      Cut a bundle of straws to same size (~2 1/2 inches long). Leave some for different lengths. These will be cut to size.
2.      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.


Created bottom of the truss bridge first, then continued to build the sides of the bridge. (These squares measure to 11 inches in length.)



3.      After creating several squares, put cross bracings diagonally (cut these to size).


4.      Put the top pieces last and enclose the truss bridge.
5.      Place the truss bridge between two desks, tables, chairs, etc.


6.      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.
Same amount as beam bridge

Added more coins
Added another bucket full of coins.
7.      Different size straws, too much tape on one side vs. the other side, etc. will create imbalance and weaknesses in the bridge structure. Try to balance taping, straw usage, etc. on all sides.


This straw and tape truss bridge was much stronger than I expected. I think I could have added another bucket of coins, but I ran out of bridge space. Maybe you can build a longer bridge and test how many buckets of coins your bridge will hold. Of course, the longer the bridge span, weaker the bridge. So, you might have to consider the bridge span vs. support strength of the abutment.

Remember, Engineering is all about failing and trying, again. So, try and try, again.