Structural Bridge Model

License : CC0 1.0 Universal
Update : 10/11/2025
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A team of civil and mechanical engineering students set out to design, build, and test a scaled model of a structural bridge using the FabLab’s digital fabrication tools — 3D printing and laser cutting. The project’s goal was to analyze how forces are distributed across a bridge structure, understand material efficiency, and test failure behavior under increasing load conditions.

Through this hands-on project, the students experienced a complete engineering workflow — from computer-aided design and simulation to real-world experimentation and optimization. The final prototype became a teaching model used by future classes to demonstrate structural behavior and the impact of design decisions.

Difficulty level :

Medium

Working time :

5 days

Supplies

  • 3D Printer: Prusa i3 MK3S+
  • Laser Cutter: Trotec Speedy 300
  • Software: Fusion 360 (design + simulation), PrusaSlicer, LightBurn
  • Materials: PLA filament (1.75 mm), 3 mm acrylic sheets

Step 1 : Research & Concept Phase

Step 2 : 3D Design and Modeling

  • The structure was modeled in Fusion 360 using parametric constraints, allowing instant adjustment of dimensions.
  • Each element (top chord, diagonals, cross beams, joints) was designed as an independent component.
  • The design was assembled digitally to verify alignment and ensure ease of physical assembly later.
  • Structural nodes and connections were optimized for interlocking fit and reduced adhesive use.

Step 3 : Simulation and Optimization

Step 4 : Fabrication

  • The students divided fabrication by method:
    Laser-cut acrylic beams for precision and speed. 3D-printed connectors and joints for customized geometry.
  • Files were sliced in (for 3D printing) and (for laser cutting).
  • Printing parameters:
    Material: PLA (1.75 mm) Layer height: 0.2 mm Infill: 60% gyroid pattern Print time: 5 hours total
  • Laser cutting used 3 mm acrylic sheets for the main beams, cut in under 20 minutes.

Step 5 : Assembly

  • The printed joints and acrylic beams were assembled on a flat jig to maintain alignment.
  • Connections were secured using press-fit design and screws — no glue required.
  • Once complete, the bridge was inspected with a digital caliper to check tolerances (< 0.5 mm deviation).
  • Aesthetic details such as color-coded members (compression vs tension) were added for educational use.

Step 6 : Load Testing

  • The prototype was mounted on a mechanical testing bench with force and displacement sensors.
  • Incremental weights were added every 500 g until the structure began to deform.
  • Data points (force vs deflection) were recorded digitally, creating a load–displacement curve.
  • Failure occurred at the mid-span joint under a maximum load of 10.5 kg — closely matching simulation predictions.
  • High-speed camera footage captured real-time deformation, providing valuable visual analysis.