======Popsicle Bridge======


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**Safety: **{{$demo.safety_description}}\\
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**Alternative titles:** Which Bridge Holds the Most Weight?
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====Summary====                   
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====Procedure====  
  - Select materials (e.g., popsicle sticks with wood glue and binder clips, or plastic straws with tape) and build at least two truss-style bridges.
  - For glued bridges, clamp joints and allow a full cure before assembly steps continue; keep both side trusses parallel and square when adding cross pieces.
  - Weigh each finished bridge to the nearest gram to enable strength-to-weight calculations.
  - Set up two equal-height supports, place a loading block at midspan, and suspend a container below the deck with rope or a hook.
  - Add weight to the container steadily (sand, water bottles, or metal weights) while observing for deflection, creaking joints, or buckling; continue until failure.
  - Record the total load at failure and identify the first point or member to fail; photograph the intact and failed bridge.
  - Compute strength-to-weight ratio as (mass of breaking load)/(mass of bridge) and compare across designs.
  - For fair tests, change only one variable at a time (design, material, span, or joint method) while keeping all others constant.




====Links==== 
Making a Popsicle Bridge & Testing It! - StructurePlanet: 
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📄 The Effect of Bridge Design on Weight Bearing Capacity - Terik Daly and Andrew Olson: [[https://www.sciencebuddies.org/science-fair-projects/project-ideas/CE_p011/civil-engineering/the-effect-of-bridge-design-on-weight-bearing-capacity]]\\

📄 How to Test Your Model Bridge - Garrett Boon: [[https://garrettsbridges.com/testing/how-to-test-your-model-bridge/]]\\


====Variations====
  * Set as a challenge for groups of students to do with limited materials.
  * Keep design constant but change material (popsicle sticks vs. straws) and compare strength-to-weight.
  * Keep materials constant but change bridge type (Warren vs. Howe vs. Pratt) to see which performs best.
  * Build identical designs with different spans to study how length affects capacity.
  * Compare joint methods (glue vs. tape vs. lap joints) on otherwise identical bridges.
  * Use a top-loading method (stacked weights) and compare results to the hanging-bucket method.




====Safety Precautions====
  * Keep feet, hands, and faces clear of the loading zone; loads can fall suddenly.
  * Use sturdy, equal-height supports and stabilize the test area to prevent tipping.
  * Lift weights with proper posture and avoid overreaching around the setup.




====Questions to Consider====
  * Which bridge had the highest strength-to-weight ratio, and why? (Likely the design that best channels forces into compression/tension along straight members with strong joints.)
  * Where did failure start, and what does that reveal about the load path? (Failure often begins at highly stressed joints or slender compression members that buckle.)
  * How does increasing span length change capacity? (Longer spans increase bending moments and typically reduce load capacity for the same cross section.)
  * Why is it important to keep supports level and load applied at midspan? (Uneven supports or off-center loading introduce asymmetry and premature failure.)
  * How could you improve your best design for the next iteration? (Stronger joints, thicker or doubled members in compression, better lateral bracing, or optimized truss geometry.)