Lateral Forces 



Lateral forces and effective lateral forces on an installation are 

 caused, respectively, by current or surge drag forces and by the effect 

 of a sloping seafloor. Drag forces are related to the maximum expected 

 peak flow velocity, the area exposed to this flow, and the shape of the 

 structure or structural members making up this area. Two worst likely 

 situations are assumed here. For most locations in water depths greater 

 than 400 feet, a peak velocity of 2.3 feet per second is assumed. For 

 shallower water and for bay entrances, narrow passages, seamount tops, 

 and similar areas of higher velocity, 5.1 feet per second is assumed. 

 Resulting simplified relationships for calculating maximum drag force, 

 based on References 15 and 16 are the following: 



Most deeper water - 



F (pounds) = 12 * A- (square feet) (1) 



Shallower water and areas of high currents - 



F, (pounds) = 60 * A., (square feet) (2) 



d 1 



where A-, is the maximum lateral projected area as defined earlier. For 

 complex structures such as that shown in Figure 2h, A-, can be taken 

 simply as the entire area encompassed by the external members of the 

 structure. 



An installation located on a slope of inclination, i, relative to 

 the horizontal, will have a component of its submerged weight acting 

 parallel to the slope. This effective lateral force, F^, is given by 

 the following equation: 



F. = W * sin i (3) 



l sub 



If the slope at the site is not known, either from bathymetric charts 

 or a topographic survey, then a typical value for "i" can be assumed 

 from the following list. Values are based partially on data from 

 Shepard and take into account typical surface roughness and 

 micro topography. 



Continental shelf (water depth less than 600 feet) : i = 2 degrees 



Continental slope (water depth between 600 feet and 4500 to 

 17,000 feet): i = 6 degrees 



Deep ocean basins (water depth greater than 4500 to 17,000 

 feet) : i = 2 degrees 



