2) Bridge Builders – Load & Strength 🌉

🏎 Bridge Builders – Load & Strength STEM Project 🎩

This STEM challenge requires you to design and build a model bridge using limited materials. You will test its ability to withstand a load and analyze the forces (tension and compression) acting on the structure. This project focuses on principles of structural engineering and material science.

The project is divided into two main phases: Quarter 1 for Design & Trifold Preparation and Quarter 2 for Building & Testing your model.

---

💡 Phase 1: Concept & Design & Trifold Preparation (Quarter 1)

This critical phase involves defining the entire experiment, documenting the design plan, and preparing all non-data sections of your trifold display. You must prepare sections 1 through 5 below for your Quarter 1 deadline.

1. Hypothesis and Research Question

What structural design or material arrangement do you think will yield the strongest bridge?

• Research Question: “How does the arrangement of materials (e.g., truss vs. beam) affect the maximum load a bridge can hold?”
• Hypothesis: If we use a triangular truss design instead of a simple beam design, the bridge will hold a greater load because the triangular structure distributes the forces of compression and tension more efficiently across the entire span.

2. Materials and Variables

List all items needed for the build and identify the elements that will be controlled or measured.

Materials You'll Need

• Balsa wood strips or dry spaghetti (structural material)
• Glue (wood glue or hot glue)
• String or wire (for hanging weights)
• Measuring tools (ruler, scale/balance)
• Weights (e.g., small buckets, sand, coins, washers, or water bottles)
• Two stable supports (to span the bridge gap – tables, blocks, or chairs)
• Small tray / plastic lid or cup to hold the weights while testing
• Safety goggles and table covering (newspaper/cardboard)

Variables

• Independent Variable: Bridge design (e.g., simple beam vs. triangular truss design)
• Dependent Variable: Maximum load held (mass before failure)
• Constants: Span distance, type of structural material, type of adhesive, approximate amount of material used, and testing method.

3. Procedures (Design & Documentation)

Your Quarter 1 procedure focuses on the trifold content. The actual building steps are performed in Quarter 2.

1. Write your project title: “Bridge Builders – Load & Strength”.
2. State your research question and hypothesis clearly on your trifold.
3. Draw a labeled diagram of at least two bridge designs you will compare (for example, a simple beam bridge and a triangular truss bridge). Indicate the expected areas of tension (pulling) and compression (pushing) on each design.
4. Explain in a short paragraph how triangulation (using triangles) increases structural stability and why engineers prefer triangles in bridges.
5. Create a simple data table template for Quarter 2 (for example: Bridge Type, Trial Number, Maximum Load Before Failure, Observations).

4. Expected Results

Based on your research and knowledge of physics, what do you expect to happen?

You should find that designs incorporating triangles (trusses) are significantly stronger than simple rectangular or beam structures, allowing the bridge to support a greater load before failure. Failure is likely to occur where the force is concentrated (the center of the span) or at weak joints.

5. Expected Conclusion (Pre-analysis)

How will your results theoretically support your hypothesis?

The experiment should support the hypothesis by demonstrating that the truss design is superior in load-bearing capacity. This is because triangular elements efficiently transfer the vertical load into horizontal forces, minimizing bending and maximizing the strength-to-weight ratio.

---

🛠 Phase 2: Working Model (Quarter 2)

In this phase, you will execute the plan you designed in Quarter 1 by building and testing your bridge models.

Construction and Testing Procedures

1. Prepare Your Workspace & Safety
   • Cover your table with newspaper or cardboard.
   • Put on safety goggles and keep hot glue guns away from water or spilled glue.
2. Build Your Bridges
   • Using your Quarter 1 designs, construct at least two bridges:
     • Bridge A: Simple beam or basic design.
     • Bridge B: Triangular truss design.
   • Cut the balsa wood/spaghetti into the required lengths based on your diagram.
   • Glue the pieces together carefully at each joint. Use small amounts of glue and press firmly so joints are strong.
   • Allow the bridges to dry completely (at least several hours or overnight) before testing.
   • Label each bridge clearly: “Bridge A” and “Bridge B”.
3. Measure Each Bridge
   • Use a ruler to measure the span length (distance between supports).
   • Use a scale/balance to measure the mass of each bridge in grams.
   • Record these measurements in your data table.
4. Set Up the Testing Rig
   • Place two stable supports (e.g., two stacks of books or blocks) on the table with a gap between them.
   • Lay the bridge across the gap so that the ends rest securely on each support.
   • Attach a hook, string loop, or small rod at the center of the bridge to hang the load tray (a small bucket, cup, or plastic lid).
5. Test Bridge A (First Design)
   • Hang the empty tray or cup from the center of the bridge.
   • Gradually add weights (sand, coins, washers, or water) slowly and evenly.
   • Watch carefully for bending, cracking sounds, or sudden failure.
   • When the bridge breaks or can no longer safely hold more weight, stop the test.
   • Measure and record the total mass supported at the moment of failure (tray + weights).
6. Test Bridge B (Truss Design)
   • Repeat the same testing procedure for Bridge B using the same type of weights and tray.
   • Again, add weight gradually until failure and record the total mass supported.
7. Repeat Trials for Accuracy
   • If possible, perform at least 3 trials for each bridge type (build multiple copies or reset the test with similar bridges).
   • Record all values in your data table and calculate the average maximum load for each design.
8. Analyze Strength-to-Weight Ratio
   • For each bridge, calculate: Strength-to-Weight Ratio = (Maximum Load Supported) ÷ (Mass of Bridge).
   • Compare which design is not only stronger, but also more efficient (strongest for its own weight).
9. Document with Photos
   • Take clear photos of each bridge before, during, and after testing.
   • Print and attach them to the center panel of your trifold as visual evidence.

---

📜 Trifold Display Board Instructions

Your final project will be presented on a standard trifold display board (approx. 37 inches high and 48 inches wide when fully open).

Board Size & Suggested Layout

Organize your board to be easy to read from left to right and top to bottom.

Panel	Suggested Content
Top Center	Project Title (Big and Bold)
Left Panel	Question / Problem, Background / Introduction, Hypothesis
Center Panel	Materials, Procedures (steps), Photos / Diagrams, Graphs / Tables (your data)
Right Panel	Results (what happened), Conclusion, Reflection / What you learned

Design Tips for a Professional Look

• Title: Use a short, clear title that can be read from across the room.
• Clarity: Print all text on white or light-colored paper.
• Font Size Guidelines:
  • Title: 72 pt or bigger
  • Headings: 32–48 pt
  • Body text: 18–24 pt
• Aesthetics: Keep it neat—align boxes, use rulers, and avoid crowded text. Use 2–3 matching colors for borders and headings.
• Visuals: Add photos, labeled diagrams, and charts (your data) to make the board engaging.

---

🎬 Helpful Videos

Bridge Building Tutorial – Popsicle Stick Truss Bridge

Use this tutorial to see step-by-step how to build a strong truss bridge using simple materials similar to your project.

Trifold Design Tutorial

Tip: Plan your layout on scrap paper first, then print, cut, and finally glue everything onto the board.