How to calculate spiral staircase dimensions
As spiral staircase requires less area as compared to traditional staircase, it saves significant square meters. Spiral staircase comes with different shapes and structural configurations. Among the configurations, the most common one contains a circular format with a central mast from which the steps are settled.
For designing the spiral staircase, the following three main factors should be considered :-
• How high should the staircase go up vertically? (space among floors)
• What is its angle of rotation?
• What is its diameter?
There should be clear idea about where the staircase will start and where it will finish at the upper level, as per the flows which are settled in the plan. It is also required to determine the angle of rotation, that is based on the diameter of the stair.
The calculation of the number of steps, is dependent on the diameter and the length of the staircase. The total length can be calculated with the following formula:
length of helical staircase = (π (Pi) x radius x angle of rotation) / 180)
Assume that the steps contain irregular shapes when they move toward the central mast, it's necessary to identify the point at which the calculation of the steps of the staircase will be done. Normally, it is found that where the user walks, is situated 2/3 from the center.
The similar method can be applied for any conventional staircase except that as the process is complicated for employing the Blondel formula, a slightly greater tolerance should be utilized.
As for instance, when there is a distance of 3.00 m among slabs and the space for a staircase of 100 cm radius, in accordance with its layout in space, the staircase should commence at the similar point where it will finish, it means that it will contain a rotation angle of 360 °. While putting the values in the previous formula, its total circumference becomes 6.28 m.
By applying the useful line, the calculated length becomes 4.18 meters where people will put steps. For 15 steps, there will be 27 cm treads and 20 cm risers.
With the use of the Blondel law, there will be a total of 67, that would surpass a traditional staircase to some extent. In a spiral staircase, that value is acceptable with specific limitations.
The minimum radius in a helical staircase should be taken as 70 centimeters, but preference should be given to stairs with minimum 80 centimeters radius. It should consider a minimum height of 2.15 meters among the steps and the roof, or the upper steps.