Design loads for PEB

Load types acting on a PEB

A pre-engineered building is designed for the specific loads of its site and use, which is why accurate load data at the start of a project is essential. The main load types are:

• Dead load (D / G): self-weight of frames, purlins, girts, cladding and insulation – typically light, often 0.10–0.20 kPa for the roof system excluding frames.
• Collateral (superimposed dead) load: permanent services, sprinklers, ceilings, lighting and ducts, commonly 0.10–0.25 kPa on industrial roofs; solar panels are added explicitly.
• Roof live load (Lr / Q): maintenance and construction load, for example 20 psf (0.96 kPa) reducible in ASCE 7-22 or an area-dependent load with a 0.25 kPa minimum for non-trafficable roofs in AS/NZS 1170.1 (plus concentrated loads).
• Floor live load (L): for mezzanines and platforms, by occupancy.
• Snow and rain loads (S, R): ground snow converted to roof snow with exposure, thermal and slope factors, plus drift at steps and parapets; rain ponding on low-slope roofs.
• Wind load (W): usually governs light PEB frames, cladding and anchor bolts – see wind design.
• Seismic load (E): governs heavy buildings, mezzanines and crane buildings in active zones – see seismic design.
• Crane loads: vertical wheel loads with impact, lateral and longitudinal forces – see crane runway systems.
• Temperature, notional and auxiliary loads: long buildings, imperfections, hung equipment.

Load combinations by region

Each code combines loads with factors that reflect the probability of simultaneous occurrence. The table summarises the main strength (ultimate) combinations; each code contains further cases and companion factors.

US practice also allows ASD combinations (for example D + 0.6W) with allowable strength design under AISC 360-22. National Annexes in Europe may set different partial factors or choose Eq. 6.10a/6.10b.

Uplift combinations such as 0.9D + 1.0W (US) or 0.9G + Wu (AU/NZ) usually govern anchor bolts, purlin bracing and base plates in light PEBs.

Load cases analysed for a PEB frame

Combinations are built from individual load cases. For a typical gable frame the designer runs more cases than the short list above suggests, because the most severe effect on each member comes from a different pattern:

Roof live load and snow are alternative variable loads on the roof and are not normally applied together at full value. Thermal effects are usually controlled by detailing rather than design: steel expands by about 12 mm per 10 m length for a 100 °C change (coefficient about 12 × 10⁻⁶ per °C), so a 120 m building may move tens of millimetres between seasons, which is why expansion joints or flexible bracing layouts are used on long buildings.

Collateral allowances and the weights of typical roofing, flooring and wall materials are listed in collateral loads and building material weights; mezzanine live loads by occupancy are in buildings with mezzanine floors.

Serviceability combinations

Deflection and drift are checked under unfactored or reduced loads, for example wind with a shorter return period. US practice (MBMA, AISC Design Guide 3) commonly uses a 10-year wind for drift; AS/NZS 1170.0 uses serviceability wind Ws; Eurocodes use characteristic, frequent or quasi-permanent combinations with limits in National Annexes. Details are given in serviceability and deflection limits.

Load data the designer needs

1. Project location, applicable building code and edition, risk / importance category and design life.
2. Basic wind speed or region, terrain and topography.
3. Ground snow load and rain intensity (where relevant).
4. Seismic parameters and site class / soil class.
5. Collateral loads, hung equipment, solar panels and future expansion.
6. Crane data, mezzanine uses and any special loads.

World Steel's engineering team establishes these parameters with the client at quotation stage, and the agreed design criteria appear on the drawing set and calculations – see design deliverables.