still unravel and ultimately fail due to structural failure of several CAUs 

 even though model tests showed a stable armor layer. Thus traditional CAU 

 design methods based solely on hydrodynamic stability are inadequate. 



17. Figure 4 shows CAU design methods, which include structural 

 response determination as suggested by various researchers. Also shown in 

 this figure are the armor layer design requirements. The table shows which 

 design requirements are satisfied by a particular design methodology. It is 

 evident that the only design methods satisfying all of the design requirements 

 are the stochastic stress methods as proposed herein. The following para- 

 graphs describe the pros and cons of each of the design methods. 



DESIGN METHODS 



DESIGN METHOD REQUIREMENTS 



Empirical - scale strength 



Deterministic - FEM 



Based on stochastic methods 



I Verify structural response in lab 

 ! Contains failure criteria 



Separate impact response 

 Incorporate strength modification 

 Incorporate fatigue 

 Reliability analysis 

 Combine varied loads 



STOCHASTIC STRESS 

 STOCHASTIC MOMENTS - LRFD 



Figure 4. CAU design methods and design requirements 



Empirical CAU design methods 



18. Determining an armor unit structural failure empirical formula and 

 verifying structural failure in the small-scale physical model simultaneously 

 with hydrodynamic stability would be advantageous because, as noted above, the 

 CAU structural strength and hydrodynamic stability are coupled. Empirical 

 methods have been developed to determine the structural response of armor 

 units in conjunction with small-scale model stability tests. Timco and 

 Mansard (1982) were successful in developing scaling criteria for the struc- 

 tural failure of concrete armor units. This methodology is very attractive 

 from a design point of view, but application of the method is expensive and 



12 



