Substituting the above quantities for a given noncircular pile cross 

 section. Equation 7-13 may be used. The coefficients K^^, etc., depend 

 only on the flow field, and are independent of pile cross-section geometry; 

 therefore, the generalized graphs are still valid. However, the hydro- 

 dynamic coefficients C^j and C/i^, depend strongly on the cross-section 

 shape of the pile. If values for Cj) and C^ corresponding to the type 

 of pile to be used are available, the procedure is identical to the one 

 presented in previous sections. 



Keulegan and Carpenter (1956) performed tests on flat plate in oscil- 

 lating flows. Equation 7-13 in the form applicable for a circular cylin- 

 der, with D taken equal to the width of the plate gave 



and 



3 < C^ < 4.5 



1.8 < Cn < 2.7 



for - > 10 (7-64) 



D 



The fact that C^ approaches the value of 1.8 as A/D (Equation 7-43) 

 increases is in good agreement with results obtained under steady flow 

 conditions. (Rouse, 1950.) 



The following procedure is proposed for estimating forces on piles 

 having sharp-edged cross sections for which no empirical data are avail- 

 able for values of C^ and C^j. 



ao The width of the pile measured perpendicular to the flow direc- 

 tion is assumed to be the diameter of an equivalent circular cylindrical 

 pile, D. 



b. The procedures outlined in the preceding sections are valid, 

 and the formulas are used as if the pile were of circular cross section 

 with diameter D. 



Co The hydrodynamic coefficients are chosen within the range given 

 by Equation 7-64, i.e., Cj^^ » 3.5 and Cj^ «= 2.0. 



This approach is approximate, and should be used with caution. More 

 accurate analyses reauire empirical determination of C^ and C^p for 

 the pile geometry under consideration,> 



Forces resulting from action of broken waves on piles are much smaller 

 than forces due to breaking waves. When pile-supported structures are con- 

 structed in the surf zone, lateral forces from the largest wave breaking 

 on the pile should be used for design. (See Section 7.12.) IVhile breaking- 

 wave forces in the surf zone are great per unit length of pile, the pile 

 length actually subjected to wave action is usually short, hence resulting 

 in a small total force. Pile design in this region is usually governed 

 primarily by vertical loads acting along the pile axis. 



7-126 I 



