Rd - Pd (d ^- 2 ♦ H/2 ) (59) 



2 



and the overturning moment is given by 



-4- 



% - ^ri d '»2+H/2 (60) 



3 



271» For the 7 and 9-second waves, these values are 



TABLE 18 - Static Pressures, Thrusts and Moments 



Breaker 

 Period T Height H^ Pressure Thrust Moment 



(seconds; (feet) (Ib./ft,^) lbs. /ft.) (ft. -lbs. /ft) 



7 9 1,060 8,750 U8,000 



9 10 1,090 9,360 52,500 



The manner in which these breaking wave pressures are applied is illustrat- 

 ed in Figure 9h< 



272, Broken Waves . - To evaluate the dynamic force due to the 11- 

 second wave, the relationships 



Pp, =^d/2)(l - X1/X2) for maximum pressures (61) 



^d" = ^m ^^c) for total thrust per foot of wall (62) 



\ = (^d-jv^'^^ * l^^V ^°^ maximum moment (63) ■ 

 may be used, where 



d » the breaker depth for the 11-second wave and equals 

 8 X 1.5 = 12 feet , (Table lU) 

 X2 = 12' X 20 - 2^0' s landward limit of uprush 



x-j^ = 2U0 - 10 X 20 = iiO' distance of wave crest to wall 



h^ = elevation of wave crest over still water level = 0.7 x 11 = 

 8 feet 



h^ = elevation of wall base above still water level measured 

 positively upward = -10 feet. 



Therefore for the 11-second wave, the dynamic pressure is 223 pounds per 

 square foot, the cfynamic thrust would be 1,780 pounds per lineal foot of 



13k 



