SSIEffects Description None References NIST (2012). Soil-structure interaction for building structures Formulae get_footing_half_width get_footing_half_length get_effective_profile_depth_rotation get_average_effective_shear_velocity_xx get_structure_effective_modal_height get_structure_to_soil_stiffness_ratio get_ssi_effects_expected get_period_lengthening_ratio