The Overloaded Community Garden Shelter
A Year 12 student is designing a shade shelter for a community garden. The brief requires it to seat six people, cost under $400 in materials, and withstand 90 km/h winds. The student's final design uses four untreated pine posts (70 × 70 mm) set 600 mm into the ground, a flat corrugated steel roof spanning 3.2 m with no cross-bracing, and a single bolt at each post-to-beam joint. The client loves the look. The student's testing consisted of standing on the roof frame to check it felt 'solid'. The project is due in four days and the student has $120 left in the budget.
1. Identify the most significant design failure in this project and justify why it matters more than the others.
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The most significant failure is structural integrity under the specified load case. The brief names 90 km/h winds, but the design has no cross-bracing and single-bolt joints, which create a mechanism: the frame can rack sideways because a single bolt acts as a pivot rather than resisting rotation. The flat roof also catches uplift. This matters more than the untreated timber (a durability issue) or the test method (an evaluation issue) because it is a safety failure against an explicit constraint. Aesthetic approval from the client does not satisfy a performance requirement. In design terms, the student has prioritised form over function and has not verified the brief's mandatory criterion.
2. The student wants to fix the design in four days with $120. Recommend a course of action and explain the trade-offs.
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A defensible recommendation is to reduce scope rather than rush a full fix. With $120 and four days, the student can add diagonal bracing using two treated timber offcuts or galvanised strap, upgrade each post-to-beam joint to a bolted bracket, and add a small roof pitch or tie-down straps for uplift. Untreated posts should at minimum be given an end-grain preservative or replaced with treated stock if cost allows. The trade-off is that a pitched roof and treated posts may exceed $120, so the student should document the compromise and present a revised brief scope (for example, a smaller 2.4 m span) to the client. This demonstrates iterative design and honest evaluation rather than pretending the original meets the brief.
3. Rewrite the student's evaluation method so it would actually test the brief.
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A valid evaluation must produce evidence against each brief criterion.
- Seating for six: measure seat width per person (typically 500–600 mm each) against the built shelter.
- Cost under $400: itemised bill of materials with receipts, totalled.
- Wind resistance: calculate or model the load. At minimum, apply the design wind pressure to the roof area, check the uplift force on the fixings, and confirm bracing resists racking. A physical test could be a weighted pull test on the frame in both directions, recorded with a spring scale.
- Durability: confirm timber treatment class is suitable for in-ground use.
Standing on the frame tests only downward static load and gives no information about wind, uplift, or lateral stability. The revised method is criterion-by-criterion, measurable, and documented.