Building Bridges

Building Bridges

Engineer a bridge strong enough to span between two surfaces holding a weight.



Duration: 2 x 45-minute Periods

Class Size: 30 Students

Group Size: 3-4 Students

Work together in teams to design bridge models using only Strawbees and construction pipes. Learn about the shape geometry composing bridges and draft a design on paper. Structure the bridge using the blueprint to build the biggest, strongest bridge to withstand a weight test.

Learning Objectives

  • Understand the basic principles of the geometric shapes used in the construction of bridges and architecture.
  • Learn about a method of physical model making engineers undertake to explain scientific concepts and begin to visualize the factors taken in building a bridge.
  • Be introduced to Civil Engineering, a discipline focused on the development and maintenance of manmade and naturally built environments and constructions.


  • 400 - Construction pipes (24 cm)
  • 500 - 1/2 sized Construction pipes
  • 500 - 1-Legged Strawbees
  • 400 - 2-Legged Strawbee
  • 300 - 3-Legged Strawbee
  • 20 - Scissors
  • 15 - Cardstock Paper
  • 15 - Pencils


  1. Cut large sheets of paper for students to draft the actual size of their bridge designs onto.
  2. To inspire and prepare your students search and print images of a beam, truss, and suspension bridge to use as talking points for this lesson.
    1. Beam Bridge: Tianjin Grand, China
    2. Truss Bridge: Little Belt, Denmark
    3. Suspension Bridge: Golden Gate, USA

Lesson Steps

1. Introduction

10 minutes

Ask your students, "What are challenges you would face as an engineer developing the bridge? Share that engineers analyze the conditions that call for a bridge and determine the design and materials needed for environmental factors. Ask your students how they think geometry helps with the design. Find and share images of bridges around the world and have your students identify what shapes do they see the most then a hypothesis as to why those shapes work.

Students will design a combination of Beam and Truss bridges to place on two surfaces, such as desks, chairs, or tables, and hold hanging weights.

2. What is the Process of Making Bridges?

10 minutes


Let your students know they will brainstorm, think of solutions to potential problems that could come up and act on them by reinforcing their bridge Strawbees! Introduce some aspects of what makes bridges safe, and how complicated foundations, balance, and weight can be when designing and building a bridge.

To build bridges with Strawbees, share with the class the parts that make up the bridge. Assembled altogether the construction pipes will make the structual elements of beams and columns with Strawbees joining them altogether. If constructed well the construction pipes will become capable of resisting tension and compression and will accept the load as long as the weight is distributed.

3. Bridge Drafting

10 minutes


Give your student teams sheets of paper, rulers, and pencils to start drafting their bridge design.

They can use pictures of bridge examples as inspiration for their designs. Students can begin trimming and assembling construction pipes and Strawbees together to ultimately build two sides of the bridge using the same drawing. Members of each group can identify how many beams will intersect at each joint and make Strawbees connectors for each one. The best bridge designs with Strawbees are when they are not loose, especially at the joints.

4. Bridge Design

40 minutes


When students begin to connect both sides of their bridges together, they will need to slip the construction pipe through the head of the Strawbees connected at a joint. To secure it in place they will need to slip a 1-Legged Strawbee through the opening of the construction pipe until you hear a click which means it's locked in place. Make sure to squeeze the opening of the straw for easy insertion of the Strawbee.

5. Testing

20 minutes


Once students are finished making their bridges, it's time to put them to the test! Arrange to have 2 tables separated from each other so they are at least 12-14 inches apart. Students will place their bridge on top of the two surfaces and step back. The weights will be placed by you, clipping on small bags of sand, magnets, or any other type of weight found in your space. For this test students will attempt at 2 different weights of 1 lb & 2 lb. For an additional challenge you can have a 5 lb weight set aside.

6. Reflection on Bridge Designs

20 minutes

At the end, ask your students their thoughts on what was successful for their bridges and what they would do that was different in their design. Poll the class Depending on the state of the bridge, you can have students redesign a new and stronger version of their previous model after going through the process.