INTRODUCTION 

 Background 



In the mid- 1960' s ocean engineering attracted considerable interest 

 in research and development on providing man with the technology to 

 work in the deep ocean. Research on undersea concrete structures was 

 initiated at this time, and exploratory test results showed much promise 

 (Ref 1) for concrete structures at depths to 3,000 feet (1,000 meters). 

 The economic payoff of the research was that massive undersea concrete 

 structures would cost about one-tenth that of metallic structures. 



For the first several years, research was directed solely to con- 

 crete spheres, but tests on cylinders started about 1970. The early 

 cylinder models had an outside diameter of 16 inches (406 mm). Param- 

 eters such as cylinder length, wall thickness, end closure conditions, 

 and concrete compressive strength (Ref 2 to 4) were investigated and 

 studied . 



The North Sea oil boom occurred in the early 1970's, and the first 

 offshore concrete platform, called Ekofisk, was built. With the success- 

 ful installation of Ekofisk in a water depth of 270 feet (90 meters), 

 industry ordered additional concrete structures for oil drilling and 

 production. A dynamic development period ensued during which it 

 became apparent that knowledge on the behavior of pressure- resistant 

 concrete structures was substantially lacking. 



In an attempt to make existing data known. Civil Engineering 

 Laboratory (CEL) test results were distributed widely (Ref 5 to 8). 

 However, the early work on cylinder structures was quite tentative 

 because of hmited data on thin-walled cylinders . 



