Created a simple spreadsheet which permits a semi-graphical approach to finding a suitable rise and run (going) for a staircase. Since the Building Code of Australia (BCA) and referenced fixed standard AS1657: platforms, walkways, stairways and ladders, have different criteria for acceptability of a stairway the first step was to graphically see the difference. For several years have had a spreadsheet which uses the formulae from both codes to determine acceptability, and by trial and error adjusted values of rise and going until achieved compatibility with both codes: but never sat down and over laid the two methods on the one chart as given in AS1657 to see where the differences lay in familar terms. The two codes have different upper and lower limits and different formula but how does that relate visually. The other issue to check at a later date is does the BCA method produce stairways in situations which AS1657 identifies as needing a ramp.

The spreadsheet is setup with 3 input parameters:

1) Rise of individual step
2) Going of individual step
3) Total height

stair1bThe chart shows two points, one in green which is the design reference point, which plots the chosen rise and going. The other point is cyan and plots the rise and going for the design height. The chart provides a visual aid to where the two design points are located and thus gives a guide as to what adjustments need to be made to bring the points within the acceptable bounding envelopes,  and over lay the two points.

stair2b

The spreadsheet uses the selected rise as the basis of calculating the number of risers (a whole number), this number needs to be less than 18 to comply with AS1657. The spreadsheet “ceil()” function is used to get the whole number of risers from the calculated value. If the value is greater than 18 then it is highlighted in red. The height is then divided by the number of risers to calculate the required step rise for the staircase. If this number does not match the value of the rise which was input into the spreadsheet then the calculated rise is highlighted in red. This may occur if the number of risers requires a smaller rise. Theerfore adjust the magnitude of the rise which was input to match the calculated value.

The total going or length of the staircase is calculated by multiplying the selected going for a step by the required number of risers.

All individiual rises and goings are checked for compatibility with the lower and upper limts of both the BCA and AS1657, a simple return value of 1 is used for compliance and 0 for non-compliance. Mere compliance with the lower and upper limits does not necessarily mean the stairway is compliant, additional checks are made to the code formula for final decision as to whether compliant or not. A stairway does not have to be compliant with both the BCA and As1657, but its helpful if it is so that future changes to building use do not require replacement of the stairway. Therefore checks are made for compliance with the individual codes and compatibility between the two codes.

A suitable rise and going for a stairway can be determined by manual trial and error using the chart as a visual aid, or the goal seek function for the spreadsheet can be used.


The spreadsheet can be downloaded here:

stairCalculator.xls


Related Products:

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  2. Structural Design of Stairs