in ASTM C39-83b (ACI Committee 215R-74 (1981)). Fatigue in concrete dolosse 

 has been investigated by Tait and Mills (1980) and Burcharth (1984). Howell 

 et al. (1992) summarize and compare the results of Burcharth and Tait and 

 Mills. Tait and Mills' results include pulsating fatigue S-N (stress versus 

 number of cycles to failure) curves, while Burcharth 's results compare impact 

 fatigue with Tait and Mills' results. Because impact stresses are not in- 

 cluded in this design methodology, only the pulsating results of Tait and 

 Mills are used. 



67. From the above comparison of fatigue pulsating S-N curves, based 

 on the research by Tait and Mills and Burcharth, a fatigue strength reduction 

 coefficient can be developed for pulsating loads as 



k F = -0.067 log 10 iV + 1 (26) 



where N is the number of design storm pulsating cycles occurring within the 

 design life. The value of N can be determined for a given coastal region from 

 knowledge of the characteristics of local storms. 

 Polos material properties 



68. The preliminary design critical strength in the dolos will be the 

 product of the concrete tensile strength f , and the fatigue reduction 

 factor, k F . The design tensile strength is highly variable, depending on 

 concrete quality. To prevent corrosion of the concrete through chemical re- 

 action with seawater and reinforcing steel, the concrete must be dense and 

 watertight. Mixing and curing procedures as well as water-cement ratios, 

 aggregate quality, and admixture types and amounts are therefore extremely 

 important. Procedures for selection of concrete materials are given in 



EM 1110-2-2000 (US Army Corps of Engineers). 



69. Tensile strength tests consist of indirect measurements including 

 flexure tests of beams, splitting tests of small cylinders, and direct meas- 

 urements including pulling tests of cylinders and rectangular blocks. Tensile 

 strength tests, in general, achieve widely varying results depending on the 

 particular concrete mix, the care taken in making the sample, and the testing 

 procedure used. Also, it is generally accepted that direct tensile test re- 

 sults are not as reliable as indirect tests because of the difficulty in 

 gripping the sample. Finally, tensile strengths based on tests of ideal 

 specimens may not be representative of the actual tensile strength because of 

 the highly complex stress state within the slender CAUs . The actual strength 



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