🎯 Learning intentions
- I can cut and fit diagonal members to convert rectangles into triangles.
- I can explain why each diagonal is either in compression or tension.
- I can document each diagonal's role in my build journal.
✅ Success criteria
- Truss #1 has all diagonals glued in place.
- Build journal photo is labelled with compression (red) and tension (blue) members.
- I can explain the word 'triangulation' in one sentence.
Do Now · 5 min
Look at your truss with top chord + verticals. It has rectangles. Push sideways on one vertical. What happens?
In your folio: "A rectangle can be ___. To make it rigid, I need to add a ___."
I Do · ~10 min Teacher demonstration
Teacher demo — cutting and fitting a diagonal at 45°.
- Measure the diagonal distance from one corner of the rectangle to the opposite corner (use ruler or dry-fit a stick).
- Mark with pencil. Cut with scissors.
- Dry-fit. If correct, glue ends with PVA.
- Hold 30 seconds. Clamp with tape if needed.
Then — for a Pratt truss:
- Diagonals slope DOWN toward the centre.
- Diagonals are in TENSION (blue).
- Verticals are in COMPRESSION (red).
We Do · ~15 min Guided practice
Together — colour-code one rectangle of your truss. Red dot on the compression member, blue dot on the tension member. Mark which corners push and which pull.
You Do · ~35 min Independent pair work
Add ALL diagonals to truss #1 (35 min).
- Starting from one end, measure and cut each diagonal individually (they may vary slightly).
- Glue one at a time. Don't batch — each needs to sit square before gluing the next.
- Tape as needed. Work methodically.
- Once all diagonals are in and dry, push gently on the corners. Truss should be RIGID — no flex.
- Take photo 3 for journal. On the photo in Google Docs, draw red dots on compression members and blue dots on tension members.
Differentiation
🪜Support
Pre-cut diagonals provided with lengths written on. Ms Gao checks each diagonal fit before glue.
🎯Core
Cut and fit all diagonals; colour-code force type in journal.
🚀Extension
Add double-diagonal (X-bracing) in the centre two bays — predict how much extra strength this will give.
Exit Ticket · 5 min
- What does triangulation do to a rectangle?
- In a Pratt truss, are the diagonals in compression or tension?
- How does your truss feel now when you push on it — rigid or wobbly?
📚 Resources for this lesson
Before you leave Quick check-in
🚩 Stuck or confused?
Click this button to flag to Ms Gao that you need a 1-to-1 next lesson. Your message is copied — paste it into a Google Classroom private comment.
📄 Export journal so far
Save your journal as a .txt file to upload to Google Classroom for Ms Gao's Friday review.
📓 Open journal + export