where F = impulse loading holding capacity 



F = short-term static holding capacity 

 st 



I = influence factor for adjusting the soil strength 



R = reduction factor for determination of cyclic 

 c 



loading holding capacity 



R = reduction factor for repeated impulses 



I = inertial factor for capacity increase under very 

 rapid loading 



I is determined from Figure 6- 1 . To use this figure the load duration 

 of the pulse of concern must be estimated and the general soil charac- 

 teristics be known or estimated. It is not possible to generalize sea- 

 floor soil characteristics, but when the undrained shear strength has 

 been estimated, the curve for normally consolidated, moderately sensi- 

 tive clays is used. If the impulse load is the first event in an anchor's 

 history or when cyclic loading is not expected, R = 1. However, when 

 cyclic loads are expected prior to the impulse event, R is the inverse 

 of the allowable double amplitude cyclic load expressed as a fraction of 

 the static short-term capacity as determined in paragraph 6.2.1. R,, 

 the reduction factor for repeated impulses, can be calculated from: 



Rj = 1.33 e" 1 - 15 f (6-2) 



where f = average frequency, in impulses per hour, for a 4-hour 

 period 



The inertial factor, I., should only be applied if the impulse duration is 

 less than 0.01 second. Values of I f can be found directly from 

 Figure 6-2. 



6.1.2 Cohesionless Soils 



The impulse loading capacity in cohesionless soil is determined by 

 the application of factors to the short-term holding capacity. 



48 



