being used for oil storage, an extra compartment to provide perforations 

 on the leeward side may not be justified. This would depend on economic 

 and physical conditions at each specific site. 



The sizes of the units required for 50- to 70-foot depths are 

 different for the oil storage and nonoil storage alternatives. If a 

 significant amount of oil storage is required, an increase in the over- 

 all size of the units is necessary. 



The extra compartment needed to incorporate perforations on the 

 leeward face of the units does not seem justified for this range of water 

 depths, unless exceptionally quiet conditions within the harbor is 

 essential. 



The preceding results are shown in Figure 2, and certain implications 

 of these results on concrete volumes and draft requirements are shown in 

 Figures 3 and 4. 



In summary, as indicated in the calculations of the Appendix: 



(a) The critical condition (maximum force on the structure) 

 can be estimated from the equivalent static load obtained from 

 maximum wave conditions, by using the Sainflou equation along 

 with a wave height reduction factor due to the perforated 

 breakwater. 



(b) Since the structure is rigid, the dynamic response due 

 to wave forces can be assumed negligible. 



(c) Maximum wave forces are greater than earthquake forces. 

 Since both earthquake forces and maximum wave forces will seldom 

 occur simultaneously, the maximum wave force was used for design. 

 A wave of 37.5 feet acting simultaneously with earthquake forces 

 will give a force equivalent to that of the maximum design of 



60 feet combined with earthquake force will still result in a 

 safety factor of 1.4, rather than the safety factor of 2 used in 

 the design. 



III. CONSTRUCTION METHODS 



1 . Previous Work . 



In recent years, construction requirements and construction capabili- 

 ties have pushed each other forward. The work contemplated here falls 

 well within the construction industry's capabilities. 



Offshore platforms for varied uses of the oil industry have been 

 constructed all over the world. With depths ranging from relatively 

 shallow water to over 300 feet, platforms have been constructed using 

 free-standing piling connected only by the platform deck itself, braced 

 templates with piles driven through the legs, and sunken caissons, some 

 floated out and sunk directly, and some floated on the side and upended 

 for sinking. 



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