2. Nonbreaking Wave Forces on Walls . 



a. General . In an analysis of wave forces on structures, a distinction 

 is made between the action of nonbreaking, breaking, and broken waves (see 

 Sec. 1,2, Selection of Design Wave). Forces due to nonbreaking waves are 

 primarily hydrostatic. Broken and breaking waves exert an additional force 

 due to the dynamic effects of turbulent water and the compression of entrapped 

 air pockets. Dynamic forces may be much greater than hydrostatic forces; 

 therefore, structures located where waves break are designed for greater 

 forces than those exposed only to nonbreaking waves. 



b. Nonbreaking Waves . Typically, shore structures are located in depths 

 where waves will break against them. However, in protected regions, or where 

 the fetch is limited, and when depth at the structure is greater than about 

 1.5 times the maximum expected wave height, nonbreaking waves may occur. 



Sainflou (1928) proposed a method for determining the pressure due to 

 nonbreaking waves. The advantage of his method has been ease of application, 

 since the resulting pressure distribution may be reasonably approximated by a 

 straight line. Experimental observations by Rundgren (1958) have indicated 

 Saniflou's method overestimates the nonbreaking wave force for steep waves. 

 The higher order theory by Miche (1944), as modified by Rundgren (1958), to 

 consider the wave reflection coefficient of the structure, appears to best fit 

 experimentally measured forces on vertical walls for steep waves, while 

 Sainflou' s theory gives better results for long waves of low steepness. 

 Design curves presented here have been developed from the Miche-Rundgren 

 equations and the Sainflou equations. 



c. Miche-Rundgren: Nonbreaking Wave Forces . Wave conditions at a 



structure and seaward of a structure (when no reflected waves are shown) are 



depicted in Figure 7-88. The wave height that would exist at the structure if 



the structure were not present is the incident wave height H. . The wave 



height that actually exists at the structure is the sum of H^ and the height 



of the wave reflected by the structure H . The wave reflection coefficient 



X equals H /H . . Wave height at the wall H is given as 

 r X u' 



H =H.+ H =(l+x)H. (7-72) 



W % r ^ 



If reflection is complete and the reflected wave has the same amplitude as the 

 incident wave, then X = I and the height of the elapotis or standing wave at 

 the structure will be 2H . . (See Figure 7-88 for definition of terms 

 associated with a elapotis at a vertical wall.) The height of the elapotis 

 crest above the bottom is given by 



y = d + h + ^-4r^ H. (7-73) 



e o I % 



where h is the height of the elapotis orbit center above SWL. 

 o 



The height of the elapotis trough above the bottom is given by 



y = d + h - ^^-^ H. (7-74) 



t o 2 t 



7-161 



