Machinery Shed Engineering
Machinery sheds demand the most from structural engineering — large clear spans, heavy point loads, wide openings, and often open-fronted bays that create maximum wind uplift. Here's how we design them.
Engineering Challenges
Machinery sheds are the most structurally demanding shed type for several reasons:
- Large clear spans — typically 18–30m to accommodate headers, tractors, and implements without internal columns obstructing access
- Open-fronted bays — many machinery sheds have one or more open faces for drive-through access, creating dominant openings that dramatically increase internal wind pressure coefficients (up to +0.7 Cpi)
- Heavy point loads — overhead cranes, hoists, and monorails for lifting equipment create concentrated loads the frame must be designed for
- High eave heights — 4.5–6m clear to accommodate tall machinery, increasing wind exposure and column bending moments
- Wide roller doors — 4.5–6m wide doors create large unbraced openings in the wall framing that require portal or jamb framing
Typical Design Approach
Most machinery sheds use portal frame construction — rigid frames with moment-resisting knee connections that provide clear spans without internal bracing in the frame direction. For spans over 18m, portal frames are almost always the most economical and practical solution.
Key design parameters:
- Frame spacing: 6–9m bays (wider = fewer frames but heavier sections)
- Column sections: typically 310UB/360UB for 18–24m spans, welded plate sections for 24m+
- Rafter sections: haunched UB sections with deeper sections at the knee (highest bending moment zone)
- Purlins: Z-sections at 1.0–1.5m spacing, designed for wind uplift plus dead load
- Bracing: tension rod or tube bracing in the longitudinal direction; portal action in the transverse direction
Crane Beam Design
Many machinery sheds include overhead crane beams or monorail tracks for lifting headers, engines, and heavy equipment. The crane beam design must account for:
- Wheel loads — the weight of the crane plus the lifted load concentrated at two or four wheel points
- Lateral surge — horizontal forces from the crane accelerating, braking, and slewing
- Fatigue — repeated load cycling if the crane is used regularly (AS 4100 fatigue provisions)
- Deflection limits — stricter than typical shed members; span/500 for crane runway beams to ensure smooth crane operation
- Column design — columns supporting crane beams must resist the additional bending, axial, and lateral forces from crane operation
A 5-tonne overhead crane on an 18m span shed adds significant forces to the columns and footings that aren't present in a standard machinery shed.
Typical Specifications
| Parameter | Typical Range |
|---|---|
| Clear span | 15–30m |
| Eave height | 4.5–6.5m |
| Bay spacing | 6–9m |
| Roof pitch | 7.5°–15° |
| Frame type | Portal frame (hot-rolled steel) |
| Column sections | 250UB–460UB or welded plate |
| Cladding | Colorbond 0.42–0.48mm BMT |
| Footing type | Pier footings with thickened slab edge |
| Engineering cost | $3,200+GST (flat fee) |
Frequently Asked Questions
What's the maximum clear span for a machinery shed?
Portal frames can economically span up to 30–35m. Beyond 35m, alternative systems like truss frames or multi-bay arrangements become more cost-effective. Most farm machinery sheds are 18–24m clear span, which comfortably accommodates modern headers and wide farm equipment.
Does an open-fronted shed need more engineering?
Yes. Open-fronted sheds create a dominant opening that increases internal pressure coefficients under wind load. This means higher uplift on the roof and higher horizontal forces on the columns compared to an enclosed shed of the same size. The frame, connections, and footings all need to be designed for these increased forces.
Can I add a crane beam later?
Only if the original design allows for it. Adding a crane beam to a shed not designed for one typically requires column, footing, and connection upgrades — often as expensive as building it right the first time. If you think you might want a crane in future, tell your engineer upfront so the design can accommodate it.
How much does a machinery shed cost to build?
Construction costs vary widely: $120–$250 per m² for a basic open-fronted shed, $180–$350/m² for enclosed sheds with concrete floors. A typical 24m × 18m (432m²) machinery shed might cost $80,000–$150,000 to build, plus $3,200+GST for engineering.
Do I need council approval for a machinery shed?
Almost always yes. Any shed over the exempt threshold (typically 10m²) requires a building permit with engineering documentation. Rural/farming zones may have more relaxed planning requirements, but the building permit and engineering are still required.