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# Bridge Building Challenge

<div style="text-align: center;"><img src="imgs/img_in_image_box_1782_52_2405_248.jpg" alt="Image" width="25%" /></div>


Goal: Design and build a model bridge that spans a given distance and holds the maximum load possible using the provided materials. Your bridge must be strong, stable, and efficient!

Materials:

Popsicle sticks

Wood glue

String or tape

• Cardboard base (supports)

## Constraints:

- Small weights (for testing)

- The bridge must span 30 cm between the supports.



Only the provided materials may be used.

The bridge must be no wider than 10 cm.

Build time: 60 minutes.

Testing will be done by placing weights at the center of the bridge until it fails.

## Think Like an Engineer!

Common Bridge Shapes

A bridge must resist different types of forces and distribute the load to the supports.

<div style="text-align: center;"><img src="imgs/img_in_image_box_1342_1254_1640_1388.jpg" alt="Image" width="12%" /></div>


Triangular Truss

Compression: squishing force

Tension: pulling force

→ strong and stable

<div style="text-align: center;"><img src="imgs/img_in_image_box_1341_1449_1633_1564.jpg" alt="Image" width="11%" /></div>


Howe Truss

Shear: forces sliding across each other

→ good for heavy loads

Bending: caused by the load pushing down on the bridge

<div style="text-align: center;"><img src="imgs/img_in_image_box_1314_1603_1679_1765.jpg" alt="Image" width="14%" /></div>


Arch Bridge

→ compression only

## Load and Strength (Algebra)

Load (L) is the total weight the bridge holds. If the bridge holds 5 weights and each weight is 20 g:

 L = 5w 

where w = weight of one mass

L = 5(20) = 100 g

Your goal is to MAXIMIZE L (the load) before failure!

Example Calculation:

If your bridge holds 8 weights (20 g each) and the span is 30 cm:

Convert to Newtons (1 g ≈ 0.0098 N)

 P = 160g×0.0098 ≈ 1.57N 

 M = 7.5P = 7.5(1.57) ≈ 11.78N· cm 

Stress (σ) is the force on a material

divided by the area (A) of the material.

 L = 8(20) = 160g 

 σ = F/A 

If a stick has a cross-sectional area of 0.2 cm2 and the force on it is 12 N:

 σ = 12/0.2 = 60N/cm2 

Stronger designs spread the load across more members, reducing stress.

Bending Moment (M) at the center of a simply supported beam with a center load:

where P = load

 M = PL/4 

 L = spanlength 

For our bridge, L = 30 cm

Good design

Balance of Strength, Stability, and Efficiency!

 S0,M = (P(30))/4 = 7.5P(N· cm) 

Testing Procedure:

1. Place the bridge on the supports.

2. Add one weight at a time to the center.

3. Record the total load.

4. Continue until the bridge fails.

5. The team with the highest load wins!

☆ Plan carefully. Build strong. Test fairly. Improve together! ☆