Design codes
Structural design to Eurocode in Struxt3D
How Struxt3D applies the Eurocodes: EN 1990 combinations, EN 1991 loads, the EN 1998 spectrum and EN 1992, 1993 and 1995 member checks, with a worked example.
The Eurocodes are the European family of structural standards: one code for the basis of design, one for actions, and one per material. When you choose Eurocode as the design code, Struxt3D takes its load combinations, imposed loads, wind pressure, seismic spectrum, material grades and member checks from that family. This tutorial lists exactly what the app uses, walks through a design, and checks a few numbers by hand so you know what the results mean.
Struxt3D uses the recommended values of the Eurocodes. Your country's National Annex can change partial factors, ψ factors, wind and seismic parameters. Treat the results as a sound first design, then confirm the nationally determined parameters for your site.
Which Eurocode parts Struxt3D uses
| Part | Topic | Used for |
|---|---|---|
| EN 1990 | Basis of structural design | Ultimate combinations (eq. 6.10), the seismic combination (eq. 6.12b), ψ factors |
| EN 1991-1-1 | Imposed loads on buildings | Floor live loads by use |
| EN 1991-1-4 | Wind actions | Peak velocity pressure, terrain category II |
| EN 1992-1-1 | Concrete structures | Beams, columns, slabs, walls, footings |
| EN 1993-1-1 | Steel structures | Steel members, including lateral-torsional buckling; cables (6.2.3) |
| EN 1993-1-8 | Design of joints | Bolted and welded steel connections |
| EN 1995-1-1 | Timber structures | Glulam members (kmod 0.8, γM 1.25) |
| EN 1998-1 | Earthquake resistance | Type 1 design spectrum, behaviour factor q, directional combination |
Load combinations
Struxt3D builds the combinations for the load cases your model has. Each wind direction (+X, −X, +Y, −Y) gets its own combination. With earthquake on, the X and Y response-spectrum results are combined as ±(EX + 0.3EY) and ±(0.3EX + EY) (EN 1998-1 4.3.3.5.1), so every seismic row below becomes four combinations.
| Combination | Source | Meaning |
|---|---|---|
| 1.35D + 1.5L | EN 1990 eq. 6.10 | Gravity, imposed load leading |
| 1.35D + 1.5L + 0.9W | eq. 6.10, ψ0 = 0.6 on wind | Imposed load leading, wind accompanying |
| 1.35D + 1.05L + 1.5W | eq. 6.10, ψ0 = 0.7 on imposed | Wind leading |
| 1.0D + 1.5W | favourable permanent load | Uplift and overturning |
| D + 0.3L + E | eq. 6.12b, ψ2 = 0.3 | Seismic design situation |
| D + L (service) | characteristic | Deflection checks only |
Earth pressure (on retaining walls) takes the dead-load factor. The seismic mass includes 30 % of the live load (ψ2 = 0.3). See Loads and load combinations for why combinations exist at all.
Imposed loads
The Floor use you pick in Supports & loads sets the live load on every floor panel. Roofs and bridge decks get their own value.
| Use | qk (kN/m²) |
|---|---|
| Office | 3.0 |
| Residential | 2.0 |
| Retail | 4.0 |
| Storage | 7.5 |
| Roof (not accessible) | 0.4 |
| Footbridge deck | 5.0 |
Finishes and services (1.5 kN/m² by default) are added to the dead load, together with the self-weight of members, slabs and walls. Concrete weighs 2500 kg/m³ including its reinforcement.
Wind
EN 1991-1-4 starts from the basic wind speed, a 10-minute mean speed (26 m/s by default). Struxt3D turns it into a peak velocity pressure with the exposure factor of terrain category II (open country):
Look up vb,0 for your site in the National Annex wind map and type it into Wind speed. Direction, season, orography and other terrain categories are not applied. Read more in Wind loads.
Earthquake
Turn on Earthquake and Struxt3D runs a response-spectrum analysis in X and Y with the EN 1998-1 Type 1 spectrum (3.2.2.5, β = 0.2). You give the design ground acceleration ag (in g, already multiplied by the importance factor γI), the ground type, and the structural system, which sets q.
| Ground type | S | TB (s) | TC (s) | TD (s) |
|---|---|---|---|---|
| A rock | 1.00 | 0.15 | 0.4 | 2.0 |
| B very dense sand, stiff clay | 1.20 | 0.15 | 0.5 | 2.0 |
| C dense or medium-dense sand | 1.15 | 0.20 | 0.6 | 2.0 |
| D loose soil | 1.35 | 0.20 | 0.8 | 2.0 |
| E surface alluvium on rock | 1.40 | 0.15 | 0.5 | 2.0 |
| Structural system | q |
|---|---|
| Ductile moment frame (DCM, αu/α1 = 1.3) | 3.9 |
| Ordinary moment frame | 1.5 |
| Braced frame | 4.0 |
| Walls or core | 3.0 |
| Elastic (no ductility) | 1.0 |
The spectrum is floored at 0.2ag beyond TC. Modes are combined with CQC. The response spectrum tutorial explains the method.
Materials and sections
| Material | Grades offered (default first) |
|---|---|
| Structural steel | S355, S275, S460 (E = 210 GPa) |
| Concrete | C30/37, C25/30, C40/50, Ecm = 22 ((fck + 8)/10)0.3 GPa |
| Reinforcement | fyk = 500 MPa, γs = 1.15 |
| Glulam | GL24h, GL28h, GL32h |
Steel beams come from the IPE range (IPE 200 to IPE 600, then HEB 600 to HEB 1000), columns from HEB 160 to HEM 500, and tubes from metric CHS and SHS. Steel resistance uses γM0 = 1.0, and column buckling uses the EN 1993-1-1 buckling curves. Concrete uses αcc = 0.85 and γc = 1.5.
Member and element checks
- Steel members are checked to EN 1993-1-1: section classification, resistance, flexural and lateral-torsional buckling and the interaction equations 6.61/6.62. See steel beam design and steel column design.
- Concrete beams, columns, slabs, walls and footings follow EN 1992-1-1, with the EN 1992 stress block, minimum and maximum reinforcement, shear links and punching. See RC beam design.
- Timber members use EN 1995-1-1 6.2/6.3 with kmod = 0.8 and γM = 1.25.
- Steel connections (fin plates, end plates, base plates, gussets, splices) follow EN 1993-1-8.
Deflections are checked under the service combination D + L against span/250 by default; change the limit in Design › Design settings….
Worked example: a four-storey office frame
- Open the template. Click Open the template above, or pick Multi-storey frame in the app.
- Choose the code. In Materials, set Design code to Eurocode. Grades switch to S355 and C30/37 and the sections to IPE/HEB.
- Set the loads. In Supports & loads, pick Office, keep finishes at 1.5 kN/m², wind at 26 m/s, and turn on Earthquake with ag = 0.22 g, ground C, ductile moment frame.
- Run. Press F5 to analyse, then F6 to design. Open File › Calculation report… to see each check with its EN clause.
Check 1: the gravity combination on a slab
With a 200 mm slab: self-weight 2500 × 9.81 × 0.20 = 4.91 kN/m², plus finishes 1.5 kN/m², gives gk = 6.41 kN/m². The office load is qk = 3.0 kN/m².
Pick 1.35D + 1.5L in the results' load selector and compare a slab's reaction with this value times its tributary area.
Check 2: the wind pressure at 10 m
Check 3: the spectrum plateau
The Modes table gives the periods. A mode at 0.9 s reads 0.162 × 0.6 / 0.9 = 0.108 g.
What you still need to check
- National Annex values: γ factors, ψ factors, the choice between eq. 6.10 and 6.10a/b, wind and seismic parameters.
- Snow, thermal, accidental and construction loads: not generated; add them by hand as extra loads.
- Wind details: terrain categories other than II, orography, cscd, internal pressure and local zones.
- Seismic details: capacity design, P-Δ (θ), accidental torsion, the Type 2 spectrum and the vertical component are not included.
- Fire, fatigue and durability classes beyond the default cover.
The accuracy and limitations page lists what the solver itself assumes.