(d) Selection of Armor Unit, Concrete Density, and Structure 

 Slope Based on First Cost (Construction Cost) . The preceding analysis is 

 considered the first cost of the structure. To complete the analysis, average 

 annual maintenance and repair costs should be established for each alternative 

 and for a range of design wave heights. Maintenance and repair costs may 

 modify the conditions established here as the most economical based on first 

 cost. 



1. Type of unit: tribar 



2. Weight of unit: 11.5 metric tons 



3. Structure slope: cot 6 = 1.5 



4. Unit weight of concrete: 24.87 kN/m 



5. Cost per 100 meter of structure: $3,180,000 

 Stability Check 



W = 



Wp H" 



% (s^ - l) 



Kd = 10.0 



Wj, = 24.87 kN/m 



cot 6 = 1.5 



= 2.47 



cot g 



(24.87) (6)^ 



10.0 (2.47 -1)^(1. 5)(9. 806) 

 W = 11.5 metric tons 



•3 



6. Volume of concrete per 100 m: 5794 m 



7. Number of armor units per 100 m: 1288 



8. Thickness of armor layer: 3.37 m 



9. Volume of first underlayer per 100 m: 5988 m 



10. Thickness of first underlayer: 1.52 m 



11. Weight of underlayer stone: 1.15 metric tons 



8-73 



