Hay Shed Engineering
Hay sheds present unique engineering challenges — open sides for ventilation create maximum wind exposure, stacked bales generate significant stored loads, and fire risk demands adequate separation.
Engineering Challenges
- Open-sided design — hay sheds are typically open on 1–3 sides for ventilation and access. This creates dominant openings with internal pressure coefficients of +0.7, maximising roof uplift forces
- Stored hay loads — stacked hay bales generate significant vertical loads on the slab and horizontal thrust against any enclosed walls. A single round bale weighs 400–600kg; a stack of square bales can impose 2–5 kPa on the floor
- Wind on exposed bales — wind acting on exposed hay stacks transfers load to the frame through friction and direct pressure, creating additional forces not present in an empty shed
- Fire separation — hay is combustible. Building regulations require minimum separation distances from boundaries and other buildings. Spontaneous combustion of improperly dried hay is a real risk
- Height — hay sheds need significant eave height (5–7m) to accommodate multi-tier stacking, increasing wind exposure
Key Design Features
Ventilation vs. Wind Protection
Hay must be ventilated to prevent moisture buildup and spontaneous combustion. Open sides achieve this but create the worst-case wind loading scenario. The structural engineer must balance ventilation requirements against wind forces — often by providing open sides on the prevailing leeward faces and partial cladding on the windward face.
Column Protection
Hay shed columns are routinely struck by machinery during loading and unloading. Design considerations include:
- Concrete-filled RHS columns at ground level for impact resistance
- Steel guard rails or bollards at vulnerable corners
- Increased column section sizes to provide a safety factor against vehicle impact
Stored Load Calculations
The engineer calculates the maximum stored load based on the hay type, stacking arrangement, and shed dimensions:
| Hay Type | Bale Weight | Floor Load (stacked) |
|---|---|---|
| Small square bales | 20–30 kg each | 2–4 kPa (stacked 4–6 high) |
| Large square bales | 400–600 kg each | 3–5 kPa (stacked 3–4 high) |
| Round bales | 400–600 kg each | 2–3 kPa (stacked 2–3 high) |