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Built-up timber beams in action

A hands-on exploration of transverse shear, connection behavior, and experimental beam response

Wooden beams connected with metal screws.jpg

Overview

This activity brings a built-up beam problem from Strength of Materials into the Structural Design Lab. Student teams design, draw, fabricate, and test a double-web girder made from a wood core and plywood side panels connected by mechanical fasteners.

Why This Activity Matters

This activity helps students move beyond textbook calculations and observe how a real built-up beam behaves under load. It highlights the importance of connection details, force transfer, stiffness, and experimental response.

Activity Status

In Development

Main focus

Transverse shear. Shear flow, Connection Behavior

Course Connection

Statics, Strength of Materials

Tools / Platforms

AutoCAD, Hand Calculations, Physical Testing, Reaction Frame and Load Actuactor

Activity Type

Design-Build-Test

Team Format

Groups of 5

Mode

Physical

Key Deliverables

Construction drawings, Load Prediction, Fabricated Specimen, Reflection Report

Technical Snapshot

  • Structural system: Double-web built-up timber girder with solid-wood top and bottom chords and plywood web panels

  • Planned test span: 8-ft simply supported beam

  • Cross-section concept: Two ½-in plywood webs connected to 4 × 6 timber members at the top and bottom

  • Loading configuration: Concentrated midspan load applied through the Structural Design Lab loading system

  • Primary design variables: Mechanical-fastener type and longitudinal fastener spacing, s.

  • Force-transfer mechanism: Fasteners transfer longitudinal shear between the plywood webs and timber chords

  • Analytical basis: Bending stress, transverse shear, shear flow, and fastener force calculated from q.

  • Responses studied: Load capacity, stiffness, connection slip, deformation, and observed failure mode

  • Experimental comparison: Predicted maximum load compared with the measured test capacity and behavior

The Design Challenge

Student teams develop and test their own built-up double-web girder specimens by varying connection details, with fastener spacing serving as the primary design parameter. Some groups may also compare screw-connected and bolt-connected configurations. Each team prepares AutoCAD construction drawings, selects materials, predicts the maximum load the beam can carry, fabricates the specimen, and tests it under midspan loading in the Structural Design Lab.

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The completed girders are evaluated experimentally using the lab’s loading system, and the measured behavior is compared with analytical predictions. Students then reflect on the relationship between theory and experiment by documenting observations, test results, failure behavior, and lessons learned.

 

Full details regarding group variations, specimen geometry, materials, connection type, analytical prediction, fabrication, testing, and final deliverables are provided in the Structural Design Lab Activities Handbook.

Related Photos and Project Examples

Selected images from related fabrication, testing, or previous project examples.

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