Design a steel stair with landings

A stair looks simple, but it is a small 3D structure in its own right: sloping beams, landings at two levels, posts and connections that all have to work together. The Stair template builds a dog-leg (half-turn) steel stair — one flight up to a half landing, a second flight back to the floor landing — repeated for as many storeys as you need.

#How the stair carries load

People on the treads load the flights. Each flight spans on plan between landings on two stringers — the inclined steel beams at its sides. The stringers sit on the landing beams that frame the half and floor landings, and those beams sit on posts at the landing corners, which take the load to the ground. At the bottom, the first flight bears on pinned supports.

Two things make stairs different from floors: the live load is higher (crowds on a stair are denser than in an office), and stairs are lively — a light, long flight can bounce under footsteps. Deflection and stiffness often govern the stringers, not strength.

#Step 1 — Pick the template

1. In the gallery choose Buildings › Stair.
2. The default is a two-storey steel stair with pinned bases.

#Step 2 — Set the size

Parameter	Section	Default	Range
Storeys	Height	2	1–6
Storey height	Height	3.2 m	2.4–5 m
Flight length on plan	Stair	2.8 m	1.8–5 m
Flight width	Stair	1.2 m	0.9–2.4 m
Landing depth	Stair	1.4 m	1–2.5 m
Gap between flights	More options	0.2 m	0–1 m

Each flight rises half a storey (1.6 m by default) over its plan length. Check the geometry against your building rules: with a 175 mm riser a 1.6 m rise needs 9–10 risers, and with a 280 mm going the flight is about 2.5–2.8 m long on plan.

#Step 3 — Materials and sections

1. Choose the Design code and steel Grade.
2. Pick sections for Stringers, Landing beams and Posts. Channels or rectangular hollow sections are common for stringers; small hollow sections for posts.
3. The flights and landings are modelled as floor panels, analysed as plates with the Floor slabs thickness. The default 200 mm represents a heavy concrete-filled tread; for open steel treads use a thin value (the minimum is 80 mm), so the self-weight is not overstated. Add the actual tread weight to Finishes and services if needed.

#Step 4 — Supports and loads

1. The foot of the first flight is pinned by the template. The Bases choice (fixed or pinned) applies to the posts. Pinned posts are normal — make sure the stair is then restrained sideways (by the building or by bracing); the analysis will tell you if it is unstable.
2. Floor use sets the live load on the flights and landings. There is no "stair" use: codes ask for more on stairs than in offices (for example 3–4 kPa in Eurocode national annexes, 4.79 kPa in ASCE 7). Pick the use whose load is closest — Retail gives 4.0 kPa (Eurocode) or 4.8 kPa (AISC / ACI).
3. For an internal stair, switch Wind off. For an external stair leave it on: without cladding, wind acts as drag on the members.

#Step 5 — Analyse

Press Run analysis (F5) and check:

1. Displacement under the service combination: the largest is at mid-flight on the stringers. Rule of thumb: keep it under span/360 and, for comfort, a few millimetres.
2. Moment: the stringers act as inclined simply supported beams; landing beams carry the stringer reactions as point loads.
3. Axial in the posts — the posts under the half landing carry the most.
4. Look at Vibration modes if earthquake is on: the first vertical mode of a flight should be well above 5 Hz. You can read frequencies in the Modes table.

#Step 6 — Design

1. Press Run design (F6) with Size members for me on. The stringers and landing beams are checked for bending, shear, lateral-torsional buckling and deflection; the posts for buckling.
2. The steel connections at the post bases, the landing beam ends and the stringer ends are designed too. Show Steel connections (3D) and click a joint to see its plates, bolts and welds.
3. Generate the Calculation report and the Shop drawings — assemblies and parts for fabrication.

#Typical problems and fixes

• Unstable structure. With pinned posts and pinned flight feet, a free-standing stair can sway like a mechanism. Fix the post bases or add bracing, as the message suggests.
• Stringers pass strength but fail deflection. Use a deeper section — stiffness rises with the cube of the depth.
• Unexpectedly heavy design. Check the Floor slabs thickness: a 200 mm plate on every flight adds about 5 kN/m² of dead load.

#Rules of thumb

• Steel stringer depth ≈ span / 15 to span / 20 (span measured on plan).
• Natural frequency of a flight ≥ 5 Hz (vertical) to avoid perceptible bounce.
• Comfortable stair: 2 × riser + going ≈ 600–630 mm.