## Recommendation points

- Principles of calculating concrete stairs
- Reinforcement rules for staircases
- Formwork installation
- Pouring stairs
- Finishing work: how to simplify cladding

One of the best solutions for interfloor communication is a concrete staircase. Precast concrete products have quite categorical standardization and their use in atypical architecture is limited. In this article we will look at the process and technology of creating a concrete staircase with our own hands..

## Principles of calculating concrete stairs

In order for the staircase to be convenient for each tenant, it must be correctly calculated. You can, of course, determine the parameters empirically by measuring the height and length of the steps of a real staircase that you use and which you find comfortable. But it’s better to stick to a proven calculation methodology..

The horizontal plane of a step is usually called a tread, and the vertical plane is called a riser. The width of the tread should be sufficient so that the foot rests on it at least 80%. The safest and most comfortable treads are those with a 300 mm tread; when climbing stairs with wider steps, you are likely to lose your step, and a narrower tread will make the descent uncomfortable. The width of the flight of stairs must be at least 80 cm for easy passage of people and at least 120 cm if you plan to carry furniture or bulky items up the stairs.

Dependence of the height and width of the step on the angle of rise of the stairs

The height of the riser is selected depending on the width of the tread. For steps with a width of 300 mm, a height of 150 mm will be optimal. If you want to make the steps wider by 10 mm, the riser should be reduced by the same value and vice versa..

It is believed that the sum of the double height of the riser and the width of the tread should be equal to the average step of a person – 400–600 mm. This indicator is individual and depends on the height of the person, so if children live in the house, make the stairs safer by increasing the tread and reducing the width of each step.

Knowing the optimal riser height, divide by this value the height difference between floors, and you get the number of steps in the staircase. The fractional remainder is the height of the first frieze step. By multiplying the number of steps by the tread width, you determine the length of the horizontal projection of the staircase and determine whether the staircase fits into the space allotted for it.

If the flight of stairs does not fit, you can make it shorter by increasing the angle of rise. The most convenient and safest is a staircase slope of 26–37 °, it is more difficult to climb steeper stairs, and with a slope over 45 °, descent is possible only backwards. To determine the angle of the stairs, use the model of a right-angled triangle, in which the legs are the tread and the riser. You can calculate the angle by dividing the step height by its width and using the table of angle tangents values.

Determination of the angle of inclination of the stairs according to the height and width of the step

If you do not want to sacrifice comfort, do not change the width and height of the steps. Instead, divide the span with an inter-flight platform, make 5-6 lower steps run-in, or build a radial spiral staircase. Please note that in this case, the width of the step at the narrowest point should not be less than 100 mm..

## Reinforcement rules for staircases

A concrete staircase is a self-supporting structure that needs additional support only if the flight angle exceeds 180 °. Otherwise, in the central part of the monolithic structure, the fracture load will exceed the standard values and compensation will be required – fastening to walls or construction of support columns..

The main load in a concrete staircase falls on the reinforcement, the number of which is record-breaking in comparison with other concrete products – from 1.7 to 3% of the cross-section along the span and up to 0.8% of the cross-section in width. ST-5 reinforcement is laid along the span with a step between the rods:

- 120 mm with a rod diameter of 10 mm;
- 160 mm with a diameter of 12-14 mm;
- 180 mm with a diameter of 16 mm;
- 200 mm with a diameter over 18 mm.
Reinforcement in the lateral projection is performed in increments of 250–300 mm. Reinforcement of platforms is performed with a step of 200 mm in each direction.

Fastening of reinforcement to embedded elements in the walls is carried out not so much in order to provide additional support, but for the sake of the solidity of the structure and in order to avoid the appearance of cracks during settlement of the building. However, the monolith of the staircase must be rigidly fastened to the ceilings by means of the release of embedded reinforcement by 60-80 mm.

The reinforcement forms a mesh, folded without a gap and placed on plastic clips that regulate the protective layer of concrete 3-5 cm from each edge. Double-row reinforcement is sufficient for stairs with 18 steps, in longer spans an additional third row of longitudinal reinforcement will be required, located 5-6 cm above the main mesh.

At the crosshairs, the mesh is tied with wire or nylon clamps. Each rebar should be solid along its entire length or width, but this is not always possible on long spans or radius staircases. Therefore, it is allowed to splicate embedded elements:

- knitted with an overlap of 24 nominal diameters;
- welding with a one-sided seam with an overlap of 12 diameters;
- welding with a double-sided seam with an overlap of 6 diameters.
The steps do not need reinforcement, but to protect them from chips, it is reasonable to use a 4×50 mm steel mesh under a 2 cm layer of concrete.

## Formwork installation

Formwork for the stairs is simpler than it might seem. First, a gutter is mounted from moisture-resistant plywood or OSB, strictly horizontal in diameter and with vertical walls fastened to each other by tie bars, one for each step. The role of the gutter walls can be played by adjacent walls. On the inner surface of the walls, a thickness gauge marks the height of the ramp – the supporting slab of the staircase, which is equal to the thickness of the reinforcement plus the upper and lower protective layer. Further, with a ruler, and for a radius staircase – with a thread of a fixed length, the vertical edges of the steps are marked on the drawn line. The length of the inclined segment is equal to the square root of the sum of the squares of the height and length of the steps (Pythagorean law).

Vertical lines are drawn along the marks made, on which the height of the steps is marked. To check, set aside a horizontal line at the new mark and measure the distance between the points of intersection with the vertical and the slope of the ramp: it should be equal to the length of one step.

According to the marks applied, the boards of the formwork of the steps are installed vertically, fixing them to the walls of the gutter, the top of each step remains open. Adjacent boards are fastened with wedge-shaped spacers, one for every 80 cm of the span width. The wide part of the wedge is attached to the end of the upper board, the narrow part is superimposed on the upper edge of the lower one. Particular attention must be paid to the walls of the gutter, they will have the main load.

The formwork is supported from below with scaffolds or telescopic racks with a permissible load of up to 800 kg. Number of racks – one for every 1.2 m

^{2}surface of the ramp. To install the props to the bottom of the formwork, transverse bars 40×40 mm are screwed from below to form a semblance of an inverted ladder.## Pouring stairs

The filling of the flight of stairs between floors is performed in one stage. Manually, such an amount of concrete cannot be prepared, and you cannot vouch for the quality of the homemade mixture. Therefore, you will have to calculate the internal volume of the formwork, equal to the volume of the ramp plus the volume of one step, multiplied by their number. It is recommended to order concrete of class B30 or higher with a margin of at least 10% of the original volume to take into account losses during transportation.

The pouring of the stairs begins with the lower steps, gradually advancing as the formwork is filled and the surface is leveled. The concrete must be tamped, and at the end of the pouring, shrink it with vibration. Sagging of the mixture on the steps after shrinkage can be eliminated by adding immediately or grouting with M300 cement mortar on 500 grade cement the next day.

Concrete gains sufficient strength within 14 days. During the drying period, it is imperative to moisten the surface to avoid cracking. After two weeks, the formwork is removed and proceeds to finishing work.

## Finishing work: how to simplify cladding

There are many options for facing stairs, ranging from simple painting to the installation of special marble slabs. It is only important to give a few tips that will greatly simplify further refinement..

Tip 1.Prepare the formwork carefully. Up to complete filling of cracks and complete filling. Formwork is a form, and if its surface is perfectly flat, then after dismantling, all that remains is to eliminate minor defects in the concrete to obtain an absolutely smooth coating.

Tip 2.Iron the steps the day after pouring. If the formwork is installed correctly, in the future it will only be necessary to grind the edges a little..

Tip 3.Provide in advance the embedded elements for handrails and fences. This will not only simplify their installation, but also will not violate the strength of the structure..

Tip 4.Don’t skimp on spacers and formwork support. Even slight curvature or punching will ruin the look.

Tip 5.Make the steps of the same height, with the possible exception of the frieze.

Tip 6.Start finishing the stairs only after the complete renovation in the house.