Discrete Points (Equivalent Linear)

The option of defining the soil curves using discrete points is only applicable for the Equivalent Linear analysis. For this option, the G/Gmax and damping ratio (%) are defined as functions of shear strain (%).

This procedure was developed in the late 1960s and early 1970s. It became widely adopted in engineering applications via the program SHAKE (Schnabel et al, 1972) and SHAKE 91 (Idriss and Sun, 1992). SHAKE used discrete points to define the soil dynamic curves (Normalized shear modulus and damping curves versus shear strain).

In the Seed and Idriss, 1970 curves for sand, the normalized shear modulus versus shear strain curve reflects the reduction in shear modulus with increasing shear strain, while the damping curve versus shear strain reflects the increase in soil damping with increasing strain. The curves are commonly discretized as individual points. In the RSSeismic, these points can be entered into the Discrete Points table in the Soil Model Properties tab. The resulting graph shows the curves plotted by connecting these points.

For an example of discrete points, see Tutorial 2 - Equivalent Linear Analysis with Discrete Points.

References

Schnabel, P. B., Lysmer, J., and Seed, H. B. (1972). “SHAKE: A computer program for earthquake response analysis of horizontally layered sites.”Rep. No. EERC 72-12, Earthquake Engineering Research Center, Univ. of California, Berkeley, Calif.