4. Engineering Shapes: Columns, Trusses and Domes

 

 

Believe me this one is so much fun!

You are going to learn how to enhance the strength and stability of simple structures.  You will build and test the structures and make predictions on loads.

 

 

 

Now let’s see what Truss, Column and Dome mean.

 

Truss

Some shapes are more stable when put under a load.  When a compression (pushing) force is applied to the structure it should not bend or change shape.  It is difficult to distort a triangle: compression at one joint is balanced by tension along the opposite sides.

 

Column

Columns (long tubes) are used to hold up heavy loads, such as roofs of buildings.  The heavy load pushes on the column, setting it up in compression.  So a good column should be very strong in compression.

 

Dome

A dome is a series of trusses that must support its own dead weight as well as the live load of wind, rain, snow, or ice.  A geodesic dome is a dome formed by joining triangles together.  You can build a giant geodesic dome out of paper. The geodesic dome's strength is due to the fact that triangles are very stable shapes. The geodesic dome's design distributes loads over all the different triangles that compose it. 

 

 

4a Columns

Make a prediction: Can a toilet paper tube withstand the compression caused by your foot?

1.       Place an empty tray on the floor.  Stand an empty toilet paper tube (column) on one end in the pan.

2.    While holding on to the back of a chair with both hands, gradually press straight down on top of the column with one foot.  Continue increasing your weight on the column until it collapses.  Use this scale to rate the column's strength:

a. very weak - it crumbles or breaks with hardly any force.

b. Only fair - it can't withstand much force

c. pretty strong - it takes a lot of force to break it

d.  super strong - We can't break it!

1.      Observe the collapsed tube to see where it failed.  How can you make the column stronger, using only sand and tape?  Repeat step 2 using the second column and your new design.

Compare the ratings

 

 

 

 

 

4b. Trusses

Make a prediction: Which shape: triangle or square will be more stable?  Why?

2.    With your partner, build a triangle and a square from straws and paper clips.  To connect two straws, slip the wide end of a paper clip into the end of a straw.  Hook a second paper clip to the first.  Now insert the wide end of the second clip into a second straw.

3.    Compare the stability of the shapes.  Stand each shape up and press down on the top corner.  What happens? How much does each one bend and twist?  How hard can you press down on each shape before it collapses?

4.    Use 11 gum drops and 25 toothpicks to make a dome. Connect 5 of the toothpicks into a ring using 5 gum drops.

5.    Use 2 toothpicks and 1 gum drop to make a triangle on one side of the base 

6.    Repeat all the way around the base until you have 5 triangles sticking up.

7.    Use toothpicks to connect the gumdrops at the tops of the triangles

8.    Push 1 toothpick into each of the top gumdrops.

9.    Use 1 last gumdrop to connect these toothpicks at the top.

     

 

 

 

 

 

 

 

4c Domes

Make a prediction: Predict how many magazines you think your paper dome will be able to support

1.      Using a sheet of colored paper and starting in one corner, roll the sheet as tightly as you can to form a tube.  When you reach the other corner, tape the tube to keep if from unrolling. Repeat for 34 of one color and another 30 of a second color

2.    Now cut the tubes to make 35 longs out of the first color (23.5 cm) and 30 shorts out of the second color (22 cm). 

3.    Flatten the ends and punch holes in each end for connectors

4.     First connect 10 longs together to make the base of the dome.

5.    Next connect a long and short to each joint. Arrange then so that there are 2 longs next to each other, followed by 2 shorts. (See picture)

 

 

6.    Connect the tops of 2 adjacent shorts together to make a triangle.  Connect the next 2 longs together and so on all the way around.

7.    Connect the tops of these new triangles with arrow of shorts.  (the dome will start inward)

8.    At each joint where 4 shorts come together, connect another short sticking straight up.  Connect this short to the joints on either side with longs, forming new triangles.

9.    Connect the tops of these new triangles with a row of longs.

             

 

10. Finally add the last 5 shorts so that they meet at a single point in the center of the dome.  To test your dome's   strength, see how many magazines you can load on top.

 

 

 

 

 

 

 

 

 

Discussion

How can you make your dome stronger without interrupting the space underneath it?

 

 

 

4. Shapes Report Sheet

 

Group Name: J ____________________