Elliptical staircase is a staircase that is formed or shaped like an egg or ellipse. Elliptical is used to describe an orbit or round shape that is not perfectly circular but nothwithstanding originated from circles with one or more focal points, in otherwords it can be oval or ellipse in shape.
This type of stair could be an offshoot of perfect circle in that is having just one focal point, this type is called helical stair and is the type we are discussing on this article. Though same principle can be used to form other shapes you want only that focal points will be more than one.
An helical staircase is a staircase formed from a curve formed by a straight line drawn on a plane when that plane is wrapped around a cylindrical surface of any kind, especially a perfect cylinder with a central focal point as shown in diagram below.
Check these samples— http://tinyurl.com/nkvk2vl
Elliptical stairs are the most difficult to construct especially when it is concrete, as you know stairs can be made of wood,steel,concrete etc
The difference between elliptical stair and the spiral stair is that spiral are perfect circular stairs and are always anchored on a column/pillarat the center to help in carrying the weight, while elliptical/helical are mostly left to stand with points on the ground floor and the connecting upper floor.
2)1”by12”by12” boards/planks (just your normal planks you buy in sawmill)
4)granite stones of very small thickness/granules-(half inch)
7)And of course a good carpenter..lol
To do the helical stair as shown on plan you must first have a proper understanding of the span the stair will cover, the starting point and the final connecting point on the upper floor.
To calculate the expanse of stairs remember your secondary school mathematics, calculate the circumference of circle for the parent circle which is 2? r
i.e 2 x 22/7 xradius
Assuming our radius of the circle is 4m, then the circumference/length of the circle is 2 x 4 x22/7=25.
But remember our stairs covers only the semi circle, therefore the circumfence or length of the semicircle is 25/2=12.5m
Taking the height of room as 3m, we are expected to share the risers and threads evenly to fall at the end of 12.5m
The normal thread is usually 0.3m, but dividing 12.5m by 0.3m will give us 42 threads , this is much ,to make the stair enjoyable we can decide to widen the thread to 0.6m which will give us 21 numbers of threadsthat is desirable.
Risers are usually one number higher than threads which makes ours 22 risers. But we have 3.15m height to span. Divide 3.15 by 22 =0.143m or 143mm for each riser.
But if the stair doesn’t have a blockwall laid in curve to support it, you will have to create a temporal wall at the external line to give it a temporal support, and is also useful for your markings.
Nail your planks standing upright along the line “a” being supported at the floor under by 2 by 3 wood, join the planks together side by side, then you can begin to do your markings on the plank which serves as temporal wall, measure and draw the riser, follow by thread and vice versa until you get to the top using our established valuesof 143mm or 0.143m and 0.6m or 600mm respectively.
After the line measure the waist which could be 120mm to 150mm (waist is the conctrete between the end of thread and the bottom platform of the concrete). Mark the spot on the first riser and the last riser, draw a line to join them, this line is where the plywood will be place just as shown in pics above.
Support or brace the formwork with 2by3 wood and use bamboo as studs, then cover the edge “b” with another plywood of the riser’s height which is properly supported to give the concrete a smooth edge, then nail the same planks along the markings of the risers between “a” and “b” to form the stair risers from bottom to top after the iron bender must have placed the required iron rods to be able to support the weight of the concrete. However to get this perfectly, trace your parent circle focal point and nail to the spot on ground an iron rod or thin wood as tall as the height of the room then tie a rope which you can easily adjust round it and use it to trace the line of the plank that will form the riser which lies from “a” to “b” . Note that the thread is bigger in “b” because of a wider circumference/length.
Then mix a concrete that has granite of small thickness of half inch type with sharpsand and cement , the mixture must be pure and strong. Pour and leave for 27 days minimum before dismantling the formwork.