Terrain amplification coefficient

The ground amplification coefficient, S, takes the following value: For ρ·ab <= 0.1 g S= C/1,25; for 0.1 g < ρ·ab < 0.4 g S=C/1,25 + 3.33(ρ·ab/g-0.1)(1-C/1,25); for 0.4 g <= ρ·ab S=1. Being: C: Ground coefficient, ab: Basic seismic acceleration, ρ: Adimensional risk coefficient. It takes the value ρ=1.0 for constructions of normal importance, and ρ= 1.3 for constructions of special importance.