A design chart approach is given in Figure 3. Enter the chart 



with the structure's L/D and t/D ratio to determine the P. /f ratio. 



o o im c 



Factor of Safety 



Overall Factor of Safety . Up to this stage, the implosion pressure 

 calculated by Equations 3, 12, and 14 (or from the design chart of Fig- 

 ure 3) is a short-term strength without any factors of safety incorpor- 

 ated. Different codes of practice have different approaches to assign- 

 ing factors of safety. Without discussing the various methods, it can 

 be stated that the overall factors of safety for concrete compression 

 members range between 2.5 and 3.0. 



This report recommends the same range. A structure whose 

 intended purpose is to store liquid material might be designed with a 

 2.5 factor of safety; whereas, a structure for human occupancy should 

 have a 3.0 factor of safety as a minimum. 



The design approach in Reference 8 included a long-term loading 

 factor, \. Codes of practice typically recognize the long-term loading 

 effect in the overall factor of safety without itemizing the effect. This 

 report follows that practice. Results have recently been published on 

 concrete spheres subjected to long-term hydrostatic loading (Ref 13) 

 that have shown behavior similar to the known behavior of concrete in 

 on-land compression members . This represents some assurance that 

 following existing on-land practice is appropriate for in-ocean concrete. 



Concrete Compressive Strength . The implosion pressure is directly 

 related to the compressive strength of concrete, f ' , at the time of 

 failure. From available data (Ref 13), it appears that the strength 

 development of concrete in the ocean is different than that of the 

 standard fog-cure condition. 



The results from Reference 13 are summarized herein . 



20 



