Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	STAAD.Pro Analysis Solutions
	Subarea:	Response Spectrum Analysis
	Original Author:	Sanjib Das & Rajat Chakroborty

What is the Scale Factor (f4) that needs to be provided when specifying the Response Spectra?

The spectrum data consists of pairs of values which are Period vs. Accn.  or Period vs. Displacement. The acceleration or displacement values that you obtain from the geological data for that site may have been provided to you as normalized values or un-normalized values. Normalization means that the values of acceleration or displacement have been divided by a  number (called normalization factor) which represents some reference value.  One of the commonly used normalization factors is 'g', the acceleration due  to gravity.

If the spectrum data you specify in STAAD is a normalized spectrum data,   you should provide the NORMALIZATION FACTOR as the SCALE FACTOR. If  your spectrum data is un-normalized, there is no need to provide a scale factor(Another way of putting it is that if you provide un-normalized spectrum values, the scale factor is 1, which happens to be the default value also.) Make sure that the value you provide for the SCALE FACTOR is in accordance with the length units you have specified. (A common error is that if the scale factor is 'g', users erroneously provide 32.2 when the length unit is in INCHES. The correct SCALE FACTOR to use in this specific case would be 386.1)

STAAD will multiply the spectral acceleration or spectral displacement values by the scale factor. Hence, if you provide a normalized acceleration value of 0.5 and a scale factor of 386.4 inch/sq.sec., it has the same effect as providing an un-normalized acceleration value of   193.2 inch/sq.sec. and a scale factor of 1.0.

In Response Spectrum Analysis if code defined Response Spectrum data is used, per the IS:1893(Par-1)-2016 code, the spectral data(Sa/g) is taken by the program from the equations provided in the code, against the specified Soil Type. After getting this value from the equations, STAAD internally multiplies that quantity with the value of "g" in the current input unit.

In such a case, the SCALE Factor is given in the input as 1.