feet, and maximum observed tidal velocity is nearly 3 knots; when wind 
velocities reach 92 knots (the observed extreme) the choppy waters in- 
volve 5 feet high wave at 35-foot wave lengths. The roadway is 20 
feet above the waterline, or 14 feet above the pontoon decks, to protect 
automotive vehicles from seawater spray. Each concrete pontoon is 50 
feet wide, divided into cells 15 feet long and 12 feet wide; pontoon 
lengths range up to 360 feet; bottoms and sides are 9 inches thick, 
decks are 7 inches thick and the walls of the interior cells are 6 
inches thick. The draft of the typical pontoon is nearly 9 feet. 
Adjacent pontoons are joined by bolts spaced at 15-inch centers around 
the perimeters of the pontoons. The bolts pass through heavy concrete 
beams that are integral with the top and bottom slabs and the side walls 
of the pontoons. Two continuous floating structures were thus created, 
each being attached to a 600-foot draw span which is situated near the 
middle of the floating bridge in order to accommodate passage of air- 
craft carriers. The floating highway is anchored by means of wire 
cables that extend from the pontoons to concrete-filled anchorage blocks 
previously placed underwater; there are 42 of these gravity anchorages, 
each of which has a submerged weight of 550 tons. The pontoons were 
precast in a graving dock. Each pontoon was post-tensioned before the 
deck was cast; the tendons, composed of eight 3/8 inch diameter strands 
of seven wires each, lie in the bottom slab (at 2-foot centers) and in 
the lower portions of the walls (interior and exterior). The cost of 
construction was $20,000,000 and required three years to complete; the 
pontoon work represented $14,000,000. A severe storm early in 1960, 
when ten of the 23 pontoons had been joined, damaged the joints between 
adjacent pontoons and cracked the decks and bottom slabs of seven pontoons 
(Engineering News-Record, 1961). Repairs and modifications during 1961 
cost an additional $3,500,000. The modified design involved joining 
the pontoons with bolts supplemented by epoxy resin bonds, and post- 
tensioning the assembly (Nichols, 1964). 
Also of interest, although never built, is the floating tunnel 
proposed 19 years ago to accommodate automotive traffic across Puget 
Sound. The nearly 14,000-foot long underwater concrete tube was 
designed to have a buoyancy nearly three times the maximum live load, 
to be situated 50 feet beneath the surface so as to not obstruct ocean- 
going ships, and to be anchored to the 800-foot deep floor of Puget 
Sound. The tube was to consist of 34 precast sections, each 400 feet 
long by 60 feet wide by 30 feet high. The cross-section was to be 
similar to the outer end of binoculars, a configuration adopted for the 
BART twin-tube described previously. Precasting was to be done ina 
graving dock, necessitating 400,000 cubic yards of concrete. The 
estimated cost of this floating concrete structure was about $55,000,000 
based on 1949 price levels (Andrew, 1951). 
Hollow concrete pontoons have been used for marinas since the early 
1960's (Sellner, 1964). Customary sizes of the modular units range 
from 6 feet long by 3 feet wide by 1 foot high to 8 by 2-1/2 feet; in 
this range the wall thickness varies from 1-1/2 to 2 inches (Noble, 1964). 
