Substituting the above quantities for a given noncircular pile cross 

 section, equation (7-20) 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 hydrodynamic 

 coefficients C^ and C^ depend strongly on the cross-section shape of the 

 pile. If values for C^ and Cw 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 oscillating 

 flows. Equation (7-20) in the form applicable for a circular cylinder, with 

 D taken equal to the width of the plate, gave 



3 < C^< 4.5 

 and \ ^°^ ^^ 10 (7-71) 



1.8 < Cj^ < 2.7 



The fact that C^ approaches the value of 1.8 as A/D (eq. 7-50) 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 available for 

 values of C,. and C^ . 



(1) The width of the pile measured perpendicular to the flow direction is 

 assumed to be the diameter of an equivalent circular cylindrical pile, D . 



(2) 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 . 



(3) The hydrodynamic coefficients are chosen within the range given by 



equation (7-71); i.e., C « 3.5 and C„" 2.0 . 



M D 



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

 accurate analyses require empirical determination of Cr, and Cn 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 

 constructed in the surf zone, lateral forces from the largest wave breaking on 

 the pile should be used for design (see Sec. 1,2). While 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 results in a small total 

 force. Pile design in this region is usually governed primarily by vertical 

 loads acting along the pile axis. 



7-160 



