A steel building quotation depends on the loads before it depends on the steel price. The same footprint can be quoted at very different tonnages when one supplier assumes a light roof in a low-wind area and another allows for snow drift, a taller eave or a heavier crane.
This guide lists the load inputs a fabricator needs, how they are usually expressed, and what to do when the structural design is not finished yet. It explains general practice; the loads used for fabrication always come from the engineer responsible for the project.
The load types that change the frame
Loads are usually grouped into permanent (dead) loads, imposed (live) loads and environmental loads. Each one affects a different part of the structure.
| Load type | What it includes | What it mainly changes |
|---|---|---|
| Dead load | Self-weight of the frame, purlins, roof and wall cladding, ceiling, insulation and permanent services | Member sizes and the total tonnage |
| Live load | Roof maintenance and access, floor occupancy, storage and movable equipment | Purlins, rafters, floor beams and columns |
| Wind load | Basic wind speed or pressure, terrain and exposure, building height and openings | Lateral bracing, column fixity, anchor bolts and cladding fixings |
| Snow load | Ground snow load with roof shape, exposure and thermal factors, plus drift at steps and valleys | Purlins, rafters and columns in snow regions |
| Seismic load | Seismic hazard, soil class, importance and the chosen lateral system | Lateral system, connections and detailing |
| Crane and equipment | Crane capacity and class, impact, and vibrating or heavy equipment | Runway beams, columns, bracing and foundation loads |
What a complete load brief contains
The list below is enough for a supplier to prepare a comparable structural proposal or to check the tonnage against the engineer's design.
- The design code and edition, for example GB 50009, ASCE 7, EN 1991 or AS/NZS 1170, and the load combination rule if it differs.
- Site location, and the basic wind speed or wind pressure with the terrain or exposure category.
- Ground snow load, roof exposure and thermal condition, and whether drift has to be considered.
- Seismic parameters: hazard level, soil class, importance factor and the intended lateral system.
- Dead loads for the roof and wall build-up, including insulation, ceilings and suspended services.
- Live loads for roof access, floors, mezzanines and storage, including racking loads where relevant.
- Crane capacity, duty class, span and the required clearance, if a crane is involved.
- Any client-specified equipment, solar, sprinkler or collateral load.
- Minimum and maximum service temperature at the site.
Where the load basis appears in the quotation
A load input is not only a design line. It changes what has to be fabricated, inspected and delivered.
| If this is understated | What tends to happen |
|---|---|
| Wind speed or exposure | Bracing, anchor bolts and cladding fixings are undersized; the frame may be adequate in the shop and fail on site. |
| Snow load or drift | Purlins and rafters are overstressed, and a roof that does not drain as assumed can pond. |
| Seismic parameters | Connections lack the required ductility and detailing, even when the member sizes look adequate. |
| Crane duty or class | Deflection and fatigue become the governing check, and the runway alignment tolerance is missed. |
| Dead load build-up | Services, ceilings or a heavier roof finish are discovered late, after members are cut. |
A practical enquiry checklist
- State the code, edition and load combination rule.
- Give the location and the wind, snow and seismic parameters, or ask for a proposed design basis.
- List the dead and live loads you already know, and mark the ones still to be confirmed.
- Describe the lateral system and any movement joints or expansion joints.
- Include crane, mezzanine and equipment data, even if the supplier's scope excludes them.
- Say who is responsible for the foundation design and the anchor bolt setting plan.
- Put the load assumptions in the quotation and repeat them in the approved drawings.
This guide describes general practice for steel structure projects. It is not a design, and it does not replace the specification or the engineer responsible for your project.