Building Bridges

Lindsay @ Strawbees

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



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 straws. 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.


1/2 sized Straws
1-Legged Strawbees
2-Legged Strawbee
3-Legged Strawbee
Cardstock Paper


Lesson Split Time

Depending on needs, this lesson can be split and taught in two 45-minute periods. With a 15 minute break seperating two sessions for a break or clean-up. An additional 15 minute session at the end is for clean-up.

Bridging Teams

A large challenge for students is to focus on how to build 1 bridge structure as a team. Encourage groups to take on the following roles: the Joint Maker, creates the joints out of Strawbees pieces, the Beam Maker, the person that measures and trims the straws to size from the drawing, and the Builders, who are responsible for assembling the bridge together.

Stockpile of Cut Straws

Alternatively to letting students cut straws, use a stockpile of trimmed straws, both 1/2 and 1/3 the size of a full length straw, and set aside for students to use for future projects.

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.



Cut large sheets of paper for students to draft the actual size of their bridge designs onto.


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.

Beam Bridge: Tianjin Grand, China Truss Bridge: Little Belt, Denmark 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 straws will make the structual elements of beams and columns with Strawbees joining them altogether. If constructed well the straws 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 straws 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 straw 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 straw 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 seperated 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.


A built structure creating a pathway over an obstacle.
Beam Bridge
A structural path with at least two beams side by side and a deck, or floor, placed on top.
Truss Bridge
A bridge structure composed primarily out of triangular shapes.
Arch Bridge
A structure that pushes loads along curved foundations to dissipate the force toward the supports on the ends.
Suspension bridge
A structure with towers with vertical suspension cables attached to a deck hanging below.
A force that pushes.
A set restriction on what can be done.
The state of being stretched from force.
A twisting force.
The force from a physical body attracting another physical body with mass to its center.
A point in a structure or shape where the parts are combined together.
The physical capability of endurance and resistance of force.
A method of measuring the skill capability of a group or characteristic of something to pass through a set of conditions.

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