BEHAVIOR OF PRESTRESSED CONCRETE SUBJECTED TO LOW TEMPERATURES AND CYCLIC LOADING (CRYOGENIC, OFFSHORE)

Concrete has exhibited excellent behavior in cryogenic containment vessels for several decades under essentially static conditions. Tests were conducted to determine the response of prestressed lightweight concrete subjected to high-intensity cyclic loading and simultaneous cryogenic thermal shock, simulating the relatively dynamic conditions encountered offshore or in seismic areas.; The experimental research was divided into three phases. Phase 1 examined the mechanical properties of plain structural lightweight concrete with varying temperatures and moisture contents. These tests included compressive strength, splitting-tensile strength, Young's Modulus and Poisson's ratio. Phase 2 examined the response of uniaxially prestressed lightweight concrete subjected to fully reversible axial tension and compression together with simultaneous cryogenic shock from liquid nitrogen at -321(DEGREES)F (-196(DEGREES)C). These tests, and the tests in Phase 3, simulated an accidental release of liquefied natural gas (LNG) at -260(DEGREES)F (-160(DEGREES)C) on the hull of an offshore concrete containment vessel subjected to severe wave loading such as could be encountered in the North Atlantic. In Phase 3, biaxially prestressed concrete slabs were subjected to cyclic membrane shear, under cryogenic conditions, simulating the wave loading conditions in the sides and longitudinal bulkheads of an offshore concrete containment vessel.; Lightweight concrete has several attractive properties for cryogenic service including: (1) very low permeability, (2) good strain capacity, (3) relatively low thermal conductivity, and (4) a low modulus of elasticity. Experimental results indicated that the mechanical properties of plain lightweight concrete significantly increase with moisture content at low temperatures, while cyclic loading fatigue effects are reduced at low temperatures. Also, tests on uniaxially and on biaxially prestressed lightweight concrete both indicate that the test specimens performed well under severe cyclic loading and cryogenic thermal shock with only moderate reduction in flexural stiffness.; Supplementary tests conducted in this study indicate that conventionally reinforced concrete degrades significantly faster than prestressed concrete when subjected to cyclic loading and thermal shock. Additional tests also indicate that biaxially prestressed concrete performs well under post-elastic cyclic loading.; These test results, combined with results from earlier researchers indicate that high-quality prestressed lightweight concrete can provide adequate safety for the containment of cryogenic liquids offshore and in seismic areas.