Table 7-8 lists the concrete armor units that have been cited in 

 literature and shows where and when the tinit was developed. One of the 

 earlier non-block concrete armor imits was the tetrapod. It was devel- 

 oped and patented in 1950 by Neyrpic, Inc., o£ France. The tetrapod is 

 an unreinforced concrete shape with four truncated conical legs project- 

 ing radially from a center point. (See Figure 7-88.) International 

 patent coverage requires a royalty be paid per cubic yard of concrete 

 used in the unit. A general patent license agieement now exists between 

 Neyrpic, and the U.S. Government regarding the royalty payment for use 

 of tetrapods and quadripods. 



Figure 7-89 provides volume, weight, thickness of layers, and dimen- 

 sions of the tetrapod unit. The quadripod (T"ig. 7-88) was developed and 

 tested by the United States in 1959; details are shown in Figure 7-90. 



In 1958, R. Q. Palmer, United States, developed and patented the 

 tribar. Tliis concrete shape consists of three cylinders connected by 

 three radial arms. (See Figure 7-88.) The need for steel reinforced 

 concrete in tribars depends on the techniques of placement and the size 

 of the unit. Generally, when using land-based equipment, steel rein- 

 forcement is not required for units weighing less than 20 tons. Placing 

 any type of armor unit from a floating plant subject to wave action can 

 result in bumping of units resulting in overstress of the concrete. Some 

 form of reinforcement may be required for tribars weighing about 10 tons 

 or more when placed by floating equipment. Figure 7-91 provides tribar 

 details on the volume, weight, thickness of layers and dimensions. Accord- 

 ing to the patent rights of the tribar, the U.S. Government is granted 

 royalty-free use. 



The Dolos armor unit was developed in 1963 by E. M. Merrifield, 

 Republic of South Africa. (Merrifield and Zwambom, 1968.) The Dolos is 

 illustrated in Figure 7-88. This concrete unit closely resembles a ship 

 anchor. Generally, reinforcement is not required for units weighing up 

 to 20 tons, but for units over 20 tons reinforcement is required. 

 (Magoon and Shimizu, 1971.) This armor unit is not patented in the 

 United States. Detailed dimensions are shown in Figure 7-92. 



As noted in Table 7-6, various other shapes have been tested by the 

 Corps of Engineers. Other shapes are the modified cube and the hexapod. 

 Details of the modified cube and hexapod are shown in Figures 7-93 and 

 7-94 respectively. 



Projects using tetrapods, tribars, quadripods, and dolosse in the 

 United States, are listed in Table 7-9. 



7.377 Design of Structure Cross-Section . A rubble structure is nor- 

 mally comprised of a bedding layer and a core of quarry-run stone cov- 

 ered by one or more layers of larger stone and an exterior layer(s) of 

 large quarrystone or concrete armor units. Typical rubble-mound cross 

 sections for nonbreaking and breaking waves are shown in Figures 7-95 



7-182 



