What is the scale factor given in the IS:1893 RSA-definition dialogue box?

Answer: The spectrum ordinates defined within various code options, including IS:1893, are normalized values in which spectral accelerations are divided by gravity acceleration. The spectrum must be converted to the specific set of units used throughout the model by applying a scale factor given as the value of gravity acceleration in the current units of your model.

Note that the design spectrum of IS:1893 is actually the MCE-level spectrum which must be reduced by dividing this value by a factor of 2R, in which R is the response reduction factor. In the first run, the value of the scale factor should be SF = I*g/(2R), in which I is the importance factor. After the first run, check the base shear which develops in the model, and if this value is less than the code-prescribed minimum, then increase the scale factor of the first run such that the resultant base shear matches the code specification.

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