Factor of safety 



74. The design stress from the joint EPF can be compared to the 

 fatigue-reduced strength as follows: 



o' c yC z k F f' t (27) 



k f' 

 FS = ^fil (28) 



o' c yc 



75. If the stress exceeds or is near the strength, the factor of 

 safety will be near to or less than 1 and the designer will iterate back 

 through the preliminary design phase. For greater factors of safety, selec- 

 tion or rejection of the design may hinge on economics. The conclusion of the 

 preliminary design phase could include a comprehensive economic analysis, 

 which may lead to more iteration to determine the optimum dolos . 

 Reinforcement 



76. If the internal stresses are too high within an unreinforced 

 dolos, the designer may elect to incorporate some sort of structural rein- 

 forcement. Several types of reinforcement that have been investigated for 

 dolosse include fiber, rebar, and post- tension tendons. Fiber reinforcement 

 can add significantly to the strength but it can also be of negligible value. 

 Fibers were used in the Crescent City dolosse and the Humboldt, California 

 dolosse. There is no evidence that these dolosse have performed better or 

 worse than similar unreinforced units. 



77. The primary disadvantage of fiber reinforcement is that the fibers 

 are distributed uniformally across the section and throughout the dolos. 

 Because steel reinforcement of any kind is relatively expensive, in conven- 

 tional concrete design, steel reinforcement is generally placed at locations 

 of highest stress. Fibers are therefore not a very efficient use of reinforc- 

 ing steel. But, depending on the dolos boundary condition, position, and 

 orientation, the maximum stress can occur at a number of locations in the 

 dolos, with the location of highest tensile stress being random. But because 

 flexural shear stresses are, in general, small the maximum stresses will occur 

 close to the outer fibers of the cross section. Therefore, having fibers 

 throughout the dolos may still be an inefficient use of reinforcement. But 

 fibers tend to be less expensive than the other forms of reinforcing. A list 



35 



