To limit the probability that the design base shear for the structural analysis of the building according to the equivalent static force procedure will not take into account all the factors that affect the expected magnitude and distribution of seismic forces and displacements in the building structure, which could lead to structural failure, which could lead to harm to persons.
To limit the probability that the design base shear will include values for periods greater than 2.0 s where there is considerable uncertainty associated with those values at such long periods, which could lead to structural failure, which could lead to harm to persons.
[Clause (c)] To supersede the application of Sentence 4.1.8.11.(2) and limit the design base shear at short periods in all but the most brittle structural systems and in buildings on soils for which the determination of site amplification is problematic, on the basis that experience during earthquakes has demonstrated that damage to well designed short-period structures with even limited ductility is very unusual.