How to Calculate Staircase Concrete Volume and waist slab start point for shuttering work

Dnyan Deshmukh

Staff member
Staircase Concrete Volume and waist slab start point for shuttering work
This is most complicated question ask by many and makes us tense, Today i will try to clear the concept and boost your confidence level to answer it as well as to do it at your project.

We See the measurement for trades, risers, landings etc on drawing provided by Architect (A good Architect also specify the waist slab start and end point for doing shuttering work, if its not provided you can ask him to incorporate it in drawing and make him a good Architect ;) )

Below is one of the cross section drawn by me for illustration purpose (Staircase may or may not have such dimensions).
Stair Layout section.png
It shows typical 2 landings of 1.5 meter length (i included top landing 250mm portion in trade to make calculation simple)
It shows trade and riser dimensions and thickness of the slab.

From the above drawing we can calculate the height and length difference between two landings.
Sum of trades will give you the length which is 10 x 0.25 = 2.5 Meter
Sum of risers will give you difference between height, which is 10 x 0.15 = 1.5 meter.
Waste slab is one which starts beneath the steps of stair, so we can calculate its length.
Waist slab Length Calculation.png

We can make use of Pythagorean theorem here to calculate the waste slab length

(This image is property of wikipedia.org)

Waist slab


By this formula we get waist slab length as 2.915 meter.

If we make this line as 150mm thick slab below, it wont connect to landing and we need to extend landing on one side and reduce on other side. the ration will be same and hence need not to worry for taking it into consideration for concrete quantity calculation.
If start and end point of waist bottom slab not mention on drawing you can calculate it now, refer below image. stair angle calculation.png
If you take the vertical face all angles on right side goes add up to 180 degree and same on other hand.
You need to measure the angle from drawing.
and then using formula as shown in image you can calculate, how much bottom shutter to extend for matching the waist slab profile.

This two colored portion cancel each other on both side of landing as shown in below image (Do not worry will tell you how to calculate quantity)
area overlap study.png

After understanding this concept we can further move to calculating concrete volume in staircase, for calculation i am assuming width of landing and flight as 1.5 meter
Stair Volume Calculation.png
The above image illustrate how you should calculate the volume.

1st or floor landing = 1.5 x 0.15 x 1.5 = 0.337 cum
2nd or mid landing = 1.25 x 0.15 x 1.5 = 0.281 cum
Waist Slab = 2.915 x 1.5 x 0.15 = 0.656 cum
Steps = 10 nos
area of triangle = 0.25 x 0.15 x 1/2 = 0.018 Sqm
Volume of steps = 10 nos x 0.018 x 1.5 = 0.281 cum

So total volume of staircase use for illustration becomes = 1.555 cum

This is how i do calculate volume of concrete, Your method may differ but the ultimate result will be same.

Now here we learn
How to calculate volume of staircase concrete
How to identify from where, waist slab shuttering to be started and where to end.
 

Pankaj Sharma

Royal Member
Staff member
Staircase Concrete Volume and waist slab start point for shuttering work
This is most complicated question ask by many and makes us tense, Today i will try to clear the concept and boost your confidence level to answer it as well as to do it at your project.

We See the measurement for trades, risers, landings etc on drawing provided by Architect (A good Architect also specify the waist slab start and end point for doing shuttering work, if its not provided you can ask him to incorporate it in drawing and make him a good Architect ;) )

Below is one of the cross section drawn by me for illustration purpose (Staircase may or may not have such dimensions).
View attachment 921
It shows typical 2 landings of 1.5 meter length (i included top landing 250mm portion in trade to make calculation simple)
It shows trade and riser dimensions and thickness of the slab.

From the above drawing we can calculate the height and length difference between two landings.
Sum of trades will give you the length which is 10 x 0.25 = 2.5 Meter
Sum of risers will give you difference between height, which is 10 x 0.15 = 1.5 meter.
Waste slab is one which starts beneath the steps of stair, so we can calculate its length.
View attachment 922

We can make use of Pythagorean theorem here to calculate the waste slab length

(This image is property of wikipedia.org)

Waist slab


By this formula we get waist slab length as 2.915 meter.

If we make this line as 150mm thick slab below, it wont connect to landing and we need to extend landing on one side and reduce on other side. the ration will be same and hence need not to worry for taking it into consideration for concrete quantity calculation.
If start and end point of waist bottom slab not mention on drawing you can calculate it now, refer below image.View attachment 923
If you take the vertical face all angles on right side goes add up to 180 degree and same on other hand.
You need to measure the angle from drawing.
and then using formula as shown in image you can calculate, how much bottom shutter to extend for matching the waist slab profile.

This two colored portion cancel each other on both side of landing as shown in below image (Do not worry will tell you how to calculate quantity)
View attachment 924

After understanding this concept we can further move to calculating concrete volume in staircase, for calculation i am assuming width of landing and flight as 1.5 meter
View attachment 925
The above image illustrate how you should calculate the volume.

1st or floor landing = 1.5 x 0.15 x 1.5 = 0.337 cum
2nd or mid landing = 1.25 x 0.15 x 1.5 = 0.281 cum
Waist Slab = 2.915 x 1.5 x 0.15 = 0.656 cum
Steps = 10 nos
area of triangle = 0.25 x 0.15 x 1/2 = 0.018 Sqm
Volume of steps = 10 nos x 0.018 x 1.5 = 0.281 cum

So total volume of staircase use for illustration becomes = 1.555 cum

This is how i do calculate volume of concrete, Your method may differ but the ultimate result will be same.

Now here we learn
How to calculate volume of staircase concrete
How to identify from where, waist slab shuttering to be started and where to end.
Nice article with full Explanation.
 
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