In 1971, the Navy surveyed the impact of building a mobile, ocean basing 

 system (MOBS) j a concrete structure of sufficient size to land C5A air- 

 craft, and found that one MOBS structure (the size equivalent to about 

 20 OTEC structures) required only a small percentage of the annual 

 quantity of construction materials, especially cement .L^J 



Joining Techniques . Precast construction using concrete elements is 

 an expanding industry for on-land structures. This technology is beginning 

 to be used, quite effectively, in constructing the North Sea structures 

 and large floating barges. The advantages are shorter construction time, 

 less congestion at the site, and better quality control. To use precast 

 construction requires that the elements be joined together with adequate 

 structural integrity and watertightness under hydrostatic head. Reliable 

 joining techniques exist; however, improvements in the technology would 

 expand application and utilization of precast concrete. For example, 

 in lieu of slip-forming the walls, a more rapid approach might be to use 

 precast wall elements and slip-form the vertical joints. The critical 

 item is the quality of the joint. 



Also joining methods encompass means to couple together large struc- 

 tural components. This approach is frequently used for underwater con- 

 struction of bridge piers and subaqueous tubes. Experience in its 

 application to large floating structures, other than pontoon bridges in 

 protected waters, does not exist; however, the technology does exist. 

 Significant advancements in construction engineering techniques for 

 joining large floating elements together could reduce construction time 

 considerably. 



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