Therefore, the total force on the 2-pile group, corrected for the finite 

 amplitude design wave, is given by, 



(F ) 

 _ "* /»"«'^e amplitud e ^ 



\STotaU2-piles ~ 7f~\ \rTotaU2-piles 



(corrected ^ (computed 



for finite from Airy 



amplitude theory) 



design 

 wave) 



43 900 

 l^TotJ\2.piles = ^ (42,000) = 73,750 lbs. , say 73,800 lbs. 



************************************* 



This approach is an approximation ^ and should be limited to rough aalaula- 

 tions for checking purposes only. The use of tables of finite amplitude 

 wave properties (Skjelbria^ et al., 1960 and Beany 1972) is recommended 

 for design calculations. 



As the distance between piles becomes small relative to the wave- 

 length, maximum forces and moments on pile groups may be conservatively 

 estimated by adding the maximum forces or moments on each pile. 



The assumption that piles are unaffected by neighboring piles is not 

 valid when distance between piles is less than three times the pile diam- 

 eter. A few investigations evaluating the effects of nearby piles are 

 summarized by Dean and Harleman (1966). 



7o318 Calculation of Forces on a Nonvertical Cylindrical Pile . A single, 

 nonvertical pile subjected to the action of a two-dimensional design wave 

 traveling in the + x direction is shown in Figure 7-62. Since forces are 

 perpendicular to the pile axis, it is reasonable to calculate forces by 

 Equation 7-13 using components of velocity and acceleration perpendicular 

 to the pile. Experiments (Bursnall and Loftin, 1951) indicate this 

 approach may not be conservative, since the drag force component depends 

 on resultant velocity rather than on the velocity component perpendicular 

 to the pile axis. To consider these experimental observations, the follow- 

 ing procedure is recommended for calculating forces on nonvertical piles. 



For a given location on the pile (x^, y^, z^ in Figure 7-62), the 

 force per unit length of pile is taken as the horizontal force per unit 

 length of a fictitious vertical pile at the same location. 



************** PY^^PLE PROBLEM *************** 



GIVEN : A pile with diameter D = 4 ft. at an angle of 45° with the 

 horizontal in the x-z plane is acted on by a design wave with height 

 H = 35 ft., period T = 12 sec. in a depth d = 85 ft. 



7-121 



