Specification guide for the Counterbalanced Stair
The counterbalanced staircase is based on straight flights in the following configuration options:
All flights are in one line, with a landing at least every 17 steps (Belgium), or according to local specifications.
- Crossed stairs, Parallel to Façade
All flights are parallel to the wall. The staircase is composed of two crossed flights per story, one access landing per exit, and one intermediate landing in between two stories.
- Crossed stairs, Perpendicular to Façade
All flights are perpendicular to the wall. The staircase is composed of two crossed flights per story, one access landing per exit, and one intermediate landing in between two stories. The intermediate landings are braced to the wall to improve stability.
Flights are laid out in a square, alternatively parallel and perpendicular to the wall. In between two flights a landing is placed at each corner of the square. Each story has one access landing, three intermediate landings and four flights.
Only materials not subject to corrosion can be used. These include extruded profiles and plates of high resistance aluminum alloy, anodized 10 micron, natural mat finishing, and fasteners of stainless steel, A2-70 DaN/mm2.
No protective treatment, painting or maintenance is required, except when exposed to aggressive environments.
Welding is not allowed. Only 45° corners of landing frames, if applicable, can be reinforced via welding.
Steel is excluded, except for fasteners and in case of extreme span. In this case, an adequate isolation between steel and aluminum is applied to prevent electrolytic coupling.
The staircase can be factory painted in any RAL color via polyester powder coating.
The staircase is partly pre-assembled in the factory, using bolts and rivets. Final assembly of the staircase is executed on the construction site. The staircase is fixed to the wall with bolts and aluminum alloy profiles.
The stringboards are made of hollow profiles of 208mm x 30mm x 2mm with double chambers. The slope is 37° or 45°, with other angles available on request. They make up straight flights that have a useful width between 60cm and 120cm.
The steps are made of aluminum alloy extruded profiles. They have an anti-slip tread:
- Steps can be based on extruded profiles, covered with anti-slip tread plates, with five-bar patterns, and a thickness between (2.5mm to 4mm.
- Steps can be based on profiles with extruded longitudinal grooves and machined transversal grooves.
- Steps can be based on extruded profiles covered with anti-slip tread plates with perforations between 9mm and 14mm with standing edge, and thickness of 3mm.
Rise height: ± 18cm
Tread length: 25cm
Risers available on request.
The frames of the landings are composed of hollow profiles of 208mm x 30mm x 2mm with double chambers. Joists of at least 60mm x 20mm x 2mm and spaced at least 30cm apart are fixed in this frame. These joists support a deck made of aluminum alloy tread plates that are perforated to drain rain water. The tread plates are riveted to the joists. The tread plates are either five-bar pattern plates with a thickness of (2.5mm to 4mm), or plates with perforations of 39mm and 14mm with standing edge, and a thickness of 3mm.
The minimal width of the landings is 15cm in excess of the useful width of the steps.
The guardrails of flights and landings are linked. They are made of a handrail of at least 50mm wide with rounded edges at a radius of at least 1.5mm. They are mounted onto hollow pickets of 60mm x 25mm x 3mm with rounded edges. The pickets are fixed into the stringers and in the landing frames at least every 74cm.
In between these pickets is constructed one of the following:
- A guardrail with three round tubes of 18mm x 2mm, set parallel to the handrail and running through the pickets.
- A guardrail with square tubes of 25mm x 25mm x 1.5mm with rounded edges, placed parallel to pickets and spaced at 11cm; tubes fixed into the handrail at top and in a square tube of 30mm x 30mm x 2mm at bottom; pickets running through this tube.
- A custom made guardrail according to agreed specifications.
The height of the guardrail is at least 1m on the landings and at least 90cm on the flights, measured at the step nosing.
For secure evacuation, no part of the stair interfere with the flowing line of the handrails. The handrails are at least 40mm cleared from all obstacles.
The manufacturer can provide a children’s handrail at intermediate height, on request.
The supporting structure consists of columns or of wall bracings, depending on the stair type.
The columns or bracings are made of U-shaped or L-shaped channels of appropriate sizes, with rounded edges. They provide the required mechanical resistance.
Columns are constructed on an adequate foundation. Wall bracings are fixed by anchor bolts of adequate sizes and numbers.
4. Mechanical properties
The stair is able to support a uniformly distributed load of 102 lb/ft2 or 500 Kg/m2 on the flights (surface projected on horizontal plane) and landings, as well as a point load of 200Kg applied anywhere on the steps or landing deck (standards NBN 1-50 and NFP 06-001).
The guardrails can withstand a horizontally applied uniform load of 67 lb/ft or 100 Kg/m without permanent deformation (standards NBN 03-103, NFP 06-001 and NFP 01-012).
The manufacturer will share calculations of stability, deformations and stresses, on request.
5. Counterbalanced stairs
To prevent improper use or limit use of space at ground level, the lower flight can be counterbalanced.
The pivoting system is composed of two guiding rings of polyamide reinforced by fiberglass and a spindle in drawn stainless steel of 20mm diameter.
Two types of counterweight positioning are possible. One system is based on prolonged stringers. The lower flight has two prolonged stringers sides which project over the rotation point. The counterweight is inside these stringers. The flight is in equilibrium at rotation point.
In the cable an pulley system, the counterbalance is applied to the tip of the stair flight by a system of one or more stainless steel cables and pulleys. The cable connects to counterweights that move inside a vertically positioned hollow profile.
The flight is blocked in its upper position by a mechanism controlled by a small gate on the access landing. Opening the gate automatically releases the flight. The counterweights ensure a soft descent of the flight.
The staircase and its installation have to be inspected. The inspection report needs to be submitted to the client within one month after the installation.