a structure, waves can impart 10 cycles of load, which is a significantly 

 large number of cycles. On-land concrete is known to possess good fatigue 

 resistance if the level of stress does not exceed 50% of the com- 

 pressive strength. L J With periods of rest between cycle loadings, the 

 autogenous healing properties of concrete assist to improve the overall 

 fatigue resistance. In the ocean, the randomly varying loads due to waves 

 and lack of rest periods may require a re-evaluation of the existing design 

 guides for fatigue. 



Design for Shear . Shear is one of the more troublesome loading con- 

 ditions for concrete because of the tensile component of force. It is 

 recognized that shear stresses can be reduced by introducing precompression 

 forces. However, design guides are not available to assist in the design 

 of large shell structures to resist shear loads. 



Punching shear is another problem for concrete shell structures. 

 Curvature assists in resisting punching shear failures, but guides for 

 design are lacking. 



Design for Impact . The impact behavior of concrete structures has 

 not been adequately researched. For OTEC structures, it is most desirable to 

 understand the mechanism of impact resistance for concrete and have a 

 means of quantifying impact behavior. Concrete has considerable capacity 

 for strain energy absorption by reinforcing with closely spaced bars or 

 fiber reinforcement. Guides for the design against impact loading are 

 lacking. 



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