Actions terminology, permanent and variable loads, imposed loads by occupancy category, snow loads (EN 1991-1-3), and wind pressure (EN 1991-1-4) — from characteristic values to design input.
EN 1991 uses the term action in place of the everyday "load" to encompass forces directly applied to a structure AND indirect effects such as temperature, settlement, or shrinkage. The key classification:
| Term | EN Symbol | ASCE 7 Equivalent | Description |
|---|---|---|---|
| Permanent action | G | D (dead) | Self-weight, superimposed dead, soil pressure, prestress effects |
| Variable action | Q | L, S, W (live, snow, wind) | Occupancy imposed, snow, wind, temperature, crane loads |
| Accidental action | A | Extraordinary (blast, impact) | Explosion, vehicle impact, flood — low probability, high consequence |
| Seismic action | AE | E (earthquake) | Treated separately under EN 1998 (EC8) |
The suffix k (e.g., Gk, Qk) denotes the characteristic value — the value with an accepted probability of not being exceeded during the design working life. For imposed loads, this is the 98th percentile 50-year value. Load factors γG and γQ then produce design values Gd = γG · Gk and Qd = γQ · Qk.
Permanent actions Gk are determined primarily from material densities (EN 1991-1-1 Annex A) and structural dimensions.
| Material | Density (kN/m³) | US Equivalent (pcf) |
|---|---|---|
| Normal-weight concrete (RC) | 25.0 | 157 |
| Prestressed concrete | 25.0–26.0 | 157–163 |
| Lightweight concrete | 9.0–20.0 | 56–125 |
| Structural steel | 78.5 | 490 |
| Aluminium alloys | 27.0 | 169 |
| Timber (softwood, dry) | 4.0–6.0 | 25–37 |
| Masonry (clay brick) | 16.0–22.0 | 100–137 |
| Water | 10.0 | 62.4 |
Imposed loads qk depend on the use category of the floor area. EN 1991-1-1 Table 6.1 defines categories A through K.
| Category | Use | qk (kN/m²) | Qk (kN, point) | ASCE 7 Equiv. (psf) |
|---|---|---|---|---|
| A1 | Residential floors | 1.5–2.0 | 2.0–3.0 | 31–42 psf |
| A2 | Stairs (residential) | 2.0–4.0 | 2.0–4.0 | 42–84 psf |
| B | Office floors | 2.0–3.0 | 1.5–4.5 | 42–63 psf |
| C1 | Congregate — tables | 2.0–3.0 | 4.0 | 50 psf |
| C2 | Fixed seats, theatres | 2.5–4.0 | 4.0 | 60 psf |
| C3 | Without obstacles, corridors | 3.0–5.0 | 4.0 | 80 psf |
| C4 | Gymnasia, dancing | 4.5–5.0 | 7.0 | 100 psf |
| C5 | Crowds — large surfaces | 5.0–7.5 | 4.5 | 100+ psf |
| D1 | Retail — general | 4.0–5.0 | 4.0–7.0 | 75 psf |
| D2 | Retail — department stores | 4.0–5.0 | 7.0 | 100 psf |
| E1 | Storage — general | 7.5 | 7.0 | 250 psf |
| H | Roofs not accessible | 0.4–1.0 | 1.0 | 20 psf min |
Snow loads depend on site altitude and the National Annex ground snow map. The design snow load on a roof is:
| Location (example) | sk (kN/m²) | Flat roof s (μ=0.8) |
|---|---|---|
| UK London (zone 1, <100m) | 0.5 | 0.40 kN/m² |
| Germany Hamburg | 0.85 | 0.68 kN/m² |
| Turkey Ankara (1000m) | 1.2–1.5 | 0.96–1.20 kN/m² |
| Germany Munich (Alpn. foothills) | 2.0 | 1.60 kN/m² |
| Norway Oslo | 4.5 | 3.60 kN/m² |
Wind loads in EC1 are calculated from peak velocity pressure qp, derived from a reference wind velocity vb adjusted for orography, terrain roughness, and height. Pressure coefficients cpe then convert peak pressure to surface pressure.
| Cat. | Description | z0 (m) | zmin (m) |
|---|---|---|---|
| 0 | Open sea | 0.003 | 1 |
| I | Open country, few obstacles | 0.01 | 1 |
| II | Open with scattered obstacles (reference) | 0.05 | 2 |
| III | Suburban / forest | 0.3 | 5 |
| IV | Urban, at least 15% covered by buildings >15m | 1.0 | 10 |
For buildings ≤ 15 m height or where h/b ≤ 4 and fn > 1 Hz, the structural factor cscd = 1.0 (conservative approximation). For tall, slender, or dynamically sensitive structures, a detailed dynamic analysis per EC1 §6 is required.