The following parameters will be needed to calculate radiation damping = Half the shorter dimension of the foundation footprint = 150 ft / 2 = 75 ft for B structure’s this structure = Half the longer dimension of the overall foundation footprint = 180 ft / 2 = 90 L structure’s ft for this structure = Fixed base period = 0.39 s T Flexible base period = 0.49 s (typically the upper bound value since it will produce the = least reduction) = Effective shear wave velocity over a depth equal to below the foundation = 570 ft/s vs ‘B’ = Effective shear modulus over a depth equal to below the foundation = 1,200 k/ft2 G ‘B’ = ratio of the soil = 0.3 ν Poisson’s = Fundamental mode effective mass = 14,500 kips (from the analysis model) M* = Effective structure height at the fundamental mode = = 41.5 ft (from the h* h / (Γϕroof) analysis model) To determine the translational contribution to radiation damping, first the fictitious periods is Ty calculated. Where Then the translational contribution to radiation damping is computed as
The following parameters will be needed to calculate radiation damping B = Half the shorter dimension of the structure’s foundation footprint = 150 ft / 2 = 75 ft for this structure L = Half the longer dimension of the structure’s overall foundation footprint = 180 ft / 2 = 90 ft for this structure T = Fixed base period = 0.39 s = Flexible base period = 0.49 s (typically the upper bound value since it will produce the least reduction) vs = Effective shear wave velocity over a depth equal to ‘B’ below the foundation = 570 ft/s G = Effective shear modulus over a depth equal to ‘B’ below the foundation = 1,200 k/ft2 ν = Poisson’s ratio of the soil = 0.3 M* = Fundamental mode effective mass = 14,500 kips (from the analysis model) h* = Effective structure height at the fundamental mode = h / (Γϕroof) = 41.5 ft (from the analysis model) To determine the translational contribution to radiation damping, first the fictitious periods Ty is calculated. Where Then the translational contribution to radiation damping is computed as
121715_DesignExamples1-8.docx