An example of precast prestressed concrete construction in a 
marine environment is found in the oil-storage platform situated 35 
miles offshore in the Gulf of Mexico. The platform supports two 5,000- 
bbl tanks on a prestressed piles some of which are 192 feet long (Bruce, 
1956). This structure is situated in 37-foot-deep seawater and rises 
41 feet above mean high tide level. It is designed to withstand a 
hurricane load of 62 psf and 36-foot high waves. The piles having an 
outside diameter of 54 inches and a wall thickness of 4 inches, are 
braced horizontally and diagonally by steel pipe. The sections composing 
the platform deck are prestressed concrete slabs 48 feet long and nearly 
17 feet wide. 
Another example of a prestressed concrete platform, 254 by 136 feet 
in area and supported by 192-foot long precast prestressed concrete 
piles, is situated 28 miles offshore in the 81-feet-deep water of Lake 
Maracaibo in Venezuela. The structure was erected in conjunction with 
an offshore natural gas conservation plant. The centrifugally spun 
piles are hollow, 3 feet in diameter, wall thickness 5 inches, and 
each prestressed by 12 cables in addition to longitudinal and spiral 
reinforcement (O'Connor, 1964). 
In 1968 the Federation Internationale de la Precontrainte's 
Commission on Durability authorized a survey of the performance of pre- 
stressed concrete structures in America, Canada, Guam, Australia, New 
Zealand, Japan, Republic of China, India, and Ceylon (Szilard, 1969). 
Among eight categories of structures was the category "Wharves, Piers, 
and Quays.'' In a total of 103 of these maritime facilities, represent- 
ing those in America (72), Canada (1), Austrialia (10), and New Zealand 
(2), only one structure showed evidence of damage. In the category 
"Bridges'', in America the most serious case of damage to prestressing 
tendons (caused by corrosion) was found in the Lake Washington floating 
bridge. The survey revealed that instances of distress or failures 
were very few. The report indicates that distress is mostly the result 
of improper constructional techniques; it is also due to improper 
structural design, faulty materials, insufficiently detailed specifica- 
tions, and insufficiently strict inspection and quality control of 
concrete. 
SIGNIFICANT FLOATING STRUCTURES 
The first floating structures made of portland cement mortar, the 
forerunner of today's ferro-cement type of construction, were the 10- 
foot long reinforced mortar rowboats built in 1848 or 1849 by J. L. 
Lambot on France (Cassie, 1967 and Morgan, 1968). This patent, issued 
in 1856, describes how the mortar hull is reinforced with wire fabric 
and iron grid. More than a centruy later, one of the aforementioned 
boats was afloat (at age 118 years) in the freshwater pond on Lambot's 
estate; this boat is now on display in a French museum and a companion 
boat, 1 year younger, is boxed and in storage at Paris. 
