How to construct stairs from cold-formed sections? Engineering high-precision steel stair structures.
The construction of steel stairs requires meticulous planning and the precise selection of materials. Metal stairs manufactured from cold-formed sections combine high structural strength with manufacturing precision, directly impacting the stability of the entire assembly. Unlike traditional hot-rolled sections, CNC-fabricated cold-formed profiles offer dimensional repeatability. This precision is critical when constructing stairs that must meet the technical requirements of the EN 1090 standard.
The choice of the appropriate steel profile determines the load-bearing capacity, stiffness, and durability of the entire structure. Depending on operational loads and the installation site, stairs can be designed using C-channels, hollow sections, or angle profiles as the primary load-bearing structure. External stairs exposed to weathering require enhanced anti-corrosion protection, whereas internal industrial stairs must comply with safety standards for high-traffic utilization.
Steel profile stair construction allows for both traditional welded designs and modern bolt-on systems, which enable assembly without the need for on-site welding. Stairs should be designed with ergonomics in mind—maintaining a riser height of 16–19 cm and a minimum tread depth of 25 cm. This ensures user comfort and compliance with building codes and regulations.
Stair Planning and Design: Choosing the Right Steel Profiles for External and Internal Applications
Stair design begins with an analysis of the building’s structure and the determination of the stair type. Selecting the appropriate steel profile depends on several key factors:
Design parameters to be considered:
- Total rise (vertical height) and the number of risers
- Imposed loads (in accordance with EN 1991-1-1: min. 3,0 kN/m² for residential buildings, 5,0 kN/m² for public facilities)
- Installation site – internal vs. external environment
- Aesthetic and functional requirements
When selecting steel sections for stair structures, it is crucial to match the load-bearing elements to the design loads. Stringers—the primary structural components—are most commonly fabricated from C-channels (C200–C300) with a wall thickness of 3,0–4,0 mm. This configuration ensures high rigidity while maintaining a relatively low dead weight of the structure.
For stair spans exceeding 3,5 m, the use of S350GD steel is recommended. Its yield strength is 350 MPa—which is 51% higher than standard S235JR steel (235 MPa). By utilizing S350GD steel, it is possible to reduce the profile cross-sections while maintaining the same load-bearing capacity, leading to a reduction in structural weight by up to 25%.
Types of profiles used as load-bearing elements:
| Element | Profile | Dimensions | Mass | Application |
|---|---|---|---|---|
| Stringers | C-Channel 200-300 | 3,0-4,0 mm thickness | 5,4-9,6 kg/m | Main load-bearing stair structure |
| Tread Supports | Square Hollow Section 60×60 | 2,5-3,0 mm thickness | 4,3-5,1 kg/m | Tread mounting |
| Balustrade | Rectangular Hollow Section 40×80 | 2,0 mm thickness | 3,5 kg/m | Posts and handrails |
| Brackets | Angle Profile 50×50 | 3,0 mm thickness | 2,3 kg/m | Local reinforcement |
Planning external stairs? Steel profiles exposed to rain and moisture?
A solution incorporating enhanced anti-corrosion protection must be selected. Outdoor metal stairs require the use of a zinc-magnesium coating (e.g.: ZM310), which offers 2–3 times higher corrosion resistance than standard hot-dip galvanization.
The appropriately selected profile directly impacts the safety and durability of the entire structure. The design of steel stairs requires precise structural calculations—beam deflection under load and overall stability must be ensured in both the vertical and horizontal planes.
Cold-Formed Steel Stairs – Lightweight Load-Bearing Structures and the Advantages of LGS Technology
Steel stairs manufactured using LGS (Light Gauge Steel) technology from cold-formed sections are characterized by an exceptional strength-to-weight ratio. The load-bearing structure of stairs made from cold-formed profiles weighs 30-40% less than an equivalent made from hot-rolled structural steel, while maintaining identical load capacity and rigidity.
Cold-formed profiles are produced by shaping steel sheets on continuous roll-forming lines or press brakes. During the manufacturing process, steel sheets with a thickness of 2,0-4,0 mm are cold-bent into shapes such as C-channels. This process preserves the uniformity of the protective coating across the entire surface of the profile.
Lightweight stair structures using LGS technology offer:
- Lower foundation costs for free-standing stairs
- Structural load reduction of 200-400 kg per floor
- Easier transport and assembly
- Faster prefabrication in workshop conditions
Advantages of CNC Prefabrication: Manufacturing Precision and Speed of Stair Assembly
Stair prefabrication utilizing CNC technology ensures manufacturing precision that is impossible to achieve through traditional methods.
Advantages of CNC bending in steel stair production:
- Profile cutting in-line
- Punching of mounting holes
- Sheet metal bending at specified angles
- Tread perforation according to a specified pattern
CNC-prefabricated stairs are delivered to the construction site as complete modules with numbered components. The assembly of such a structure takes 1–2 working days and requires no welding—all connections are made using grade 8.8 bolts. As a result, the stairs can be mass-produced, reducing unit costs by 25–35%.
Stringer
Tread
Connector
Types of steel profiles for stairs – Cold-formed sections: C-channel and angle profile
The most commonly used profiles in steel stair construction are C-channels, hollow sections, and angle profiles. Each of these sections has specific properties that determine its application within the stair structure.
Stair Stringers: The Use of High-Strength Cold-Formed C-Channels
The cold-formed C-channel is the primary profile used for the stair stringer—the main load-bearing element of the structure. Stringers (also known as “cheeks”) made from C200–C300 channels are characterized by an optimal use of material, maximizing the moment of inertia while maintaining minimal profile weight.
Example: C250×80×3,5 mm C-channel technical parameters:
- Moment of inertia Iy = 4580 cm⁴
- Section modulus Wy = 366 cm³
- Mass 8,5 kg/m
Cold-formed C-channel stringers are installed in two configurations:
- Side stringers – C-channels positioned vertically on the sides of the stairs.
- Central stringers – one or two C-channels positioned under the center of the treads
C-channels with a wall thickness of 3,0–4,0 mm made of S350GD steel provide sufficient load-bearing capacity for stairs with a span of up to 6,0 m without the need for intermediate supports.
Open-Mesh and Perforated Treads – Safety and Construction Aesthetics
Open-mesh treads made from perforated sheet metal combine user safety with the visual lightness of the structure. An Rv 5-8 perforation pattern (round holes, staggered rows, 5 mm diameter, 8 mm pitch) provides:
- Weight reduction of 35-42%: Significant lowering of the dead load on the stringers, allowing for a more slender overall structure
- Effective evacuation of water and snow: Essential for outdoor stairs to prevent the accumulation of ice and puddles, ensuring year-round safety
- Anti-slip properties: The punched edges of the holes create a high-friction surface, providing excellent grip even in wet conditions
- Light transmission: Allowing light to flow between the treads in open-work (open-riser) stairs, which prevents the space underneath from becoming dark and claustrophobic
Perforated sheet metal with a thickness of 3,0–4,0 mm made of S350GD steel maintains sufficient stiffness for treads with a width of 800–1200 mm. The mounting of perforated treads to the risers is carried out using M8 countersunk bolts. After cutting, the edges of the sheet are protected by a zinc-magnesium coating, which prevents edge corrosion.
The appearance of stairs with open-work (perforated) treads is minimalist and modern. This type of steel staircase is used in office buildings, industrial facilities, containers, and modular structures.
Construction Elements: Square and Rectangular Profiles in Balustrade Systems
Square and rectangular profiles are closed sections used in balustrade systems and as risers. The closed cross-section provides uniform strength in all directions.
A stair balustrade made of closed sections consists of:
- Vertical posts: 50×100×3 mm rectangular profile spaced every 1000–1500 mm
- Handrails: 40×80×2,5 mm profile or Ø42 mm pipe
- Infill: Ø12 mm bars, mesh, or tempered glass
A 60×60×3 mm square profile used as a riser provides rigid support for the treads. Fastened to the stringer with Grade 8.8 M10 bolts, it creates a durable connection capable of transferring stair loads without the need for welding.
Step-by-Step Stair Assembly – How to Build Metal Stairs Without Welding?
Building metal stairs through bolting is a solution that combines assembly speed with functionality and the possibility of disassembly. Installing stairs without welding avoids damage to the anti-corrosion coating at weld points, prevents thermal stress, and eliminates the need for welding work on the construction site.
Stair Support Structure – Bolted Connections vs. Welding (Eliminating Thermal Stress)
The load-bearing structure of the bolted stair system relies on Grade 8.8 bolts, which provide strength comparable to welds. M10-M16 Grade 8.8 bolts have a tensile strength of 800 MPa, which is sufficient to transfer loads in stair structures with spans of up to 8 m.
Bolted metal stairs are characterized by a modular design. In the event of damage to a single tread, it can be replaced without interfering with the rest of the structure. This is a significant advantage in industrial facilities.
Ergonomics and Standards: Designing Step Height and Stair Incline
The step height and the incline of the stair flight must meet ergonomic requirements:
Riser height
- Stairs in residential buildings: 16-19 cm (optimal 17,5 cm)
- Stairs in public buildings: 14-17 cm
- Industrial stairs: 16-20 cm
Tread width: min. 25-28 cm. The pitch of the flight is determined by the formula: 2h + s = 60-65 cm. Stairs with a pitch of 30-35° are the most ergonomic and safe.
Installation of balustrades and modular finishing systems for steel stairs.
The stair balustrade is a component ensuring safety of use. The balustrade must withstand a horizontal load of 1,0 kN (residential buildings) or 3,0 kN (public buildings).
Balustrade installation:
- Rectangular section posts 50×100 mm every 1000-1500 mm.
- Mounting to stringers or step edges using M12 bolts.
- Handrail at a height of 900-1100 mm.
- Infill: vertical bars every 100-120 mm (max. clearance for a 100 mm diameter sphere).
System finishing includes handrail end caps, profile end plugs, anti-slip strips, and optional LED lighting.
Stairs with balustrad
Perforated stairs
C-type treads
Finishing and protection of stairs – S350GD steel and modern zinc-magnesium coating.
Finishing and protection of stairs have a direct impact on the durability of the entire structure as well as its aesthetics. Steel stairs must be protected as early as the production stage.
Corrosion protection: Durability of metal stairs in harsh outdoor conditions.
The durability of metal stairs under atmospheric conditions depends on the corrosion protection system. A coating such as ZM310 is a zinc-magnesium protective layer with the following composition:
- Zink (Zn): 93,5%
- Aluminium (Al): 3,5%
- Magnesium (Mg): 3,0%
- Layer thickness: 310 g/m²
Treść wiadomości Gemini
The corrosion-resistant zinc-magnesium coating works on the principle of cathodic protection. Salt spray chamber testing shows that it withstands 2000 hours without red rust, while standard galvanizing lasts only 720 hours.
The durability of the entire structure is ensured by a zinc-magnesium coating as the primary protection for all structural components. Metal stairs with a zinc-magnesium coating do not require renovation during the first 20 years of operation.
Cut edge corrosion is a typical problem with perforated treads. The zinc-magnesium coating protects the edges thanks to the cathodic effect.
Material strength: Why does S350GD steel dominate in stair construction?
S350GD steel is a high-strength structural steel for cold forming. Advantages of S350GD steel over S235JR steel:
- Yield strength: +51% (350 MPa vs 235 MPa)
- Wall thickness reduction capability: from 4,0 mm to 3,0 mm
- Structural weight reduction: 20–25%
- Maintaining the same load-bearing capacity and stiffness
The steel stair structure made of S350GD steel is characterized by low weight and high load-bearing capacity. The stiffness of the structure also increases – a higher modulus of elasticity allows for reduced deflection under load.
The entire stair structure made of S350GD profiles can be given a minimalist character – thinner profiles look lighter and more elegant. Stainless steel is an alternative for extremely aggressive environments, but the costs are 4–5 times higher.
Application in modular construction: Steel stairs as a container frame element
Steel stairs in modular construction constitute an integral part of the building structure. A residential or office container requires stairs adapted to the modular structure – lightweight, quick to assemble, and relocatable.
- Lightweight structure made of cold-formed profiles – maximum weight of 200 kg per floor level
- Bolt assembly – disassembly capability
- Modularity – segments matching the grid
- Integration with the container frame
External stairs require reinforced protection – a zinc-magnesium (ZM) coating plus optional powder coating. The modular system allows for rapid assembly (4–6 hours), transport in segments, and easy expansion.
The stability of the entire structure requires special attention in the case of self-supporting stairs. Stringers made of C200–C250 channels using S350GD steel provide sufficient stiffness for stairs up to 6 m in height.
Prefabrication of stairs for modular construction occurs simultaneously with container production, which reduces project lead times by 30–40%.
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