To limit the probability that the acceleration time-histories used in the numerical time-history method will not be spectrum-compatible and will not take into account how site amplifications affect the response of buildings subjected to ground motions, which could lead to structural failure, which could lead to harm to persons.
To direct Code users to Sentence 4.1.8.4.(7) for the determination of the design spectral response acceleration values, S(T), and their intermediate values.