Supports and loads
Set bases, pad footings, floor use, finishes, wind and earthquake inputs in Struxt3D's Supports & loads step. Self-weight and code combinations are added for you.
The Supports & loads step, titled How is it held and loaded?, is the last of the setup steps. It sets how the structure is held at its base and what acts on it. You never enter self-weight or load combinations: Struxt3D works out the weight from the sections and densities, and builds the combinations from your design code. The panel only shows the sections that apply to your model.
Bases
Choose Fixed or Pinned for the column bases. A fixed base holds all six movements and rotations; a pinned base holds the three movements and lets the column rotate. This applies to every support the template marks as a base — supports you set node by node keep their own type. The section is hidden for templates whose supports are set by the structure itself, such as rollers on a bridge or soil springs under a raft.
Supports show in purple on the model. To learn when to choose which, read Supports, joints and member end releases.
Foundations
For models on point supports, Pad footings sizes a concrete pad under every support from its reactions when you run the design. It is on by default, with two inputs:
| Input | Default | Meaning |
|---|---|---|
| Allowable bearing | 200 kPa | The soil pressure allowed under service loads (50–1000 kPa) |
| Depth of the base | 1.0 m | How far the underside of the footing is below the column base (0.3–5 m) |
Footings are not designed on rafts, wall line supports or offshore structures. See How to design a pad footing.
Floor use
For models with floors, choose the occupancy: Office, Residential, Retail or Storage. Each button shows its imposed (live) load in kN/m² from your code:
| Code | Office | Residential | Retail | Storage | Roof |
|---|---|---|---|---|---|
| Eurocode | 3.0 | 2.0 | 4.0 | 7.5 | 0.4 |
| AISC / ACI | 2.4 | 1.92 | 4.79 | 6.0 | 0.96 |
| KDS | 2.5 | 2.0 | 4.0 | 6.0 | 1.0 |
| CSA | 2.4 | 1.9 | 4.8 | 6.0 | 1.0 |
| NSCP 2015 | 2.4 | 1.9 | 4.8 | 6.0 | 1.0 |
| AS/NZS | 3.0 | 1.5 | 4.0 | 5.0 | 0.25 |
Roofs take the roof load and footbridge decks the footbridge load of the code. With NSCP 2015, a live load over 4.8 kPa (Storage) also raises the live-load factor in the wind and seismic combinations from 0.5 to 1.0 (f1).
Other loads
Finishes and services
A superimposed dead load on floors, roofs and decks — screed, ceilings, ducts — from 0 to 10 kN/m² in 0.25 steps; 1.5 kN/m² by default. It is added to the Dead case with the self-weight.
Wind
The Wind switch adds four load cases: Wind +X, Wind −X, Wind +Y and Wind −Y. Set the Wind speed (10–90 m/s) for your site. Codes that use a mean wind speed (Eurocode, KDS, CSA) ask for the basic wind speed; codes that use a gust (AISC / ACI, NSCP 2015, AS/NZS) ask for the 3-second gust — the note under the switch says which. Defaults: 26 m/s (Eurocode), 50 (AISC / ACI), 28 (KDS), 25 (CSA), 69 (NSCP 2015, about 250 km/h) and 45 (AS/NZS).
Clad structures get pressure on their cladding (windward and leeward); open structures such as towers, racks and trusses get drag on each member. See Wind loads.
Earthquake
The Earthquake switch, off by default, adds a response-spectrum analysis in X and Y: the vibration modes are found and combined by CQC. The inputs follow your code:
| Code | Inputs |
|---|---|
| Eurocode | Ground acceleration ag (g), ground type A–E |
| AS/NZS | Hazard kp·Z (g), site class Ae–Ee |
| AISC / ACI, KDS | SDS and SD1 (g) |
| CSA | S(0.2) and S(1.0) (g) |
| NSCP 2015 | Seismic zone (4 or 2), soil profile SA–SE, and in zone 4 the seismic source type (A, B, C) and the distance to it in km. The resulting Ca, Cv, Na and Nv are shown below the inputs. |
For every code you also choose the Structural system — Ductile moment frame, Ordinary moment frame, Braced frame, Walls or core or Elastic (no ductility) — which sets the behaviour factor (q, R, RdRo or μ/Sp) shown beside it. Read Earthquake design with response spectrum analysis for what these mean.
Combinations
The note at the end of the section counts the strength combinations your code gives for the cases you switched on — for example 6 strength combinations from AISC / ACI, plus D + L for deflections. The full list, with factors, is in the analysis results and the calculation report. Loads and load combinations explains how they are built.
Template loads
Some templates add loads of their own, which do not appear as inputs here: earth pressure on a retaining wall (Earth case), wave and current drag on an offshore jacket (Wave), water in a tank, a crane's wheel loads. You can add point and line loads by hand in the workspace — see Editing the model.
Show on the model
The chips at the end — Dead, Live, the wind cases and any template cases — draw that load case's loads on the model in orange, so you can check where they act. The legend under the view names the case shown.
Slab and wall thickness
The thickness of slabs and walls is set in the previous step, Materials, because it belongs with the sections.
Run the analysis
The step ends with Run analysis. It solves the model and opens the workspace on the results — see Running the analysis. You can come back to this step any time from the Setup card or Define › Supports and loads…; changing anything here clears the results until you run again.