The concrete was under sustained stress of 1,700 psi in the hoop 

 direction and 920 psi in the axial direction for 302 days . The average 

 total creep strain in the hoop and axial direction was 130 and 80 

 [jin . /in . , respectively ; these values represent a 34% and 47% increase , 

 respectively, over the short-term strain (not unusual for concrete). 

 The data gave no indication that the creep strain was nearing termina- 

 tion. 



The large penetration had little effect on the behavior of the 

 hemisphere. Again, the low stress level in the concrete might not have 

 been sufficient to produce a noticeable strain rise at the penetration. 

 In any event, it was significant that the penetrator, equivalent to 40% 

 of the structure's diameter, did not produce a harmful effect on the 

 structure . 



Watertightness . Upon retrieval of the cylinder from the 600-foot 

 (180-meter) depth after 10 months, the interior of the structure was 

 free from water that permeated the concrete walls . There was no 

 evidence of condensation, or even dampness, on the interior concrete 

 walls . * 



Results from long-term loading of concrete spheres in the ocean 

 (Ref 13) confirm this finding of watertightness. The 66-inch (1076-mm) 

 OD spheres had a wall thickness of 4.12 inches (105 mm) and were 

 located at depths that ranged from 2,000 to 5,000 feet (600 to 1500 

 meters). Some of the sphere exteriors were coated identical to the 

 SEACON structure and showed no water on the interior after 6 years in 

 the ocean . 



Implosion Test 



Depth at Implosion . The depth of implosion for the structure was 

 4,700 feet (1430 m). 



*Three quarts of water were found inside the structure due to a leak 

 in a check valve in one of the small penetrators under investigation . 



35 



