of the peak pressure pulse requires a transducer with a frequency response 

 exceeding about 1,000 cycles per second (1 kilohertz). The transducer 

 must have a good transient response and an amplitude range matched to 

 the wave dimensions used in the tests. This may require a capability of 

 measuring from 100 to 1,000 pounds per square inch, although the model 

 waves are only a few inches in height. Another important factor in 

 transducer selection is the need to avoid distortion of the pressure 

 pulse by changes in the shape or stiffness of the test structure that 

 result from the installation of the transducer in the face of the test 

 structure. Experiments at WES during the period 1963 to 1968 used two 

 types of pressure transducers in model tests of breaking wave pressure — 

 the miniature flush diaphragm strain gage and the miniature piezoelectric 

 pressure transducers. The transducers were selected on the basis of phys- 

 ical size and frequency response characteristics, and because of the ex- 

 perience with similar transducers in a large number of experiments where 

 pressures due to water shock were measured. The flush diaphragm cells 

 used were commercially available CEC Model 4-312 units. The piezoelec- 

 tric cells were fabricated at WES from zirconate ceramic elements. De- 

 tails of the experimental procedure and the equipment used in the tests 

 to determine pressures on vertical-wall structures due to breaking waves 

 were reported by Ross (1955), Garcia (1968), and Kamel (1968b). 



Pressure measurements are useful in understanding the nature of wave 

 action on structures. For nonbreaking waves when sufficient simultaneous 

 measurements will allow determination of the shape of the pressure curve 

 in the vertical, the total force per unit length of the structure can be 

 estimated with enough accuracy for design purposes. However, pressure 

 measurements alone, which provide time-pressure histories on relatively 

 small areas of the breakwater face, are not sufficient for determining 

 the force time histories needed to design structures to withstand the 

 forces of breaking waves. These forces have been measured in the lab- 

 oratory by Carr (1953, 1954a, 1954b) and by Leendertse (1962) using a 

 three -component wave force balance. The measured quantities were the 

 Qorizontal component of force, the vertical component of force, and the 

 total moment about an arbitrary horizontal reference axis. Forces on 

 vertical, inclined, and stepped barriers were investigated by Carr. The 

 geometry of the force balance is shown in Figure 6-16, where R is the 

 resultant force on the barrier; T is the horizontal component of the 

 resultant force; L is the vertical component of the resultant force; 

 Mp is the moment of the resultant force about the fixed balance pivot; 

 x and y are the horizontal and vertical distances of the pivot from 

 the toe of barrier; M is the moment of the resultant force about the 

 barrier toe (M = NL + Ty + Lx) ; 9 is the angle of inclination of the 

 resultant force from the horizontal; and c.p. is the center of pressure 

 distance (i.e., the perpendicular distance from the barrier toe to the 

 line of action of the resultant). The vertical and horizontal forces and 

 the moment about the fixed balance pivot were measured by shop-fabricated 

 force-sensing cells of 1,000-pound capacity. The cells consisted of heat- 

 treated stainless-steel bars with a milled flat gage section (about 0.375 

 inch wide and 0.08 inch thick) bonded by four Baldwin Type AB-7 gages. 

 Two gages were bonded on each side, one parallel and one transverse to 



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