A flat steel bulkhead of sandwich construction was selected as the closure for the condition where two cylinders are to be joined end-to-end. Although this is a relatively heavy closure, it provides a more convenient mating surface than a hemispherical arrangement. A vertical guide system incorporating a ball-and-funnel assembly

was selected for joining the cylinders. When the cylinders are joined, a 10 ft. by 10 ft. section may be removed from the center of each closure to -provide limited access between cylinders.

Emphasis has been placed on structural design of the closure in the first phase of this re-port. In developing the several concepts the 60 ft. diameter concrete cylinder was used as the basic case. However, a parametric study was conducted involving closures for the 20 ft. and 40 ft. diameter concrete cylinders.

Closure handling methods were emphasized in the on-land phase of the study. Using the structural calculations developed in Phase I, as a foundation, only limited additional calculations were necessary to assure concept feasibility.

Because the variation of closure weight with respect to size is more critical on land than in the buoyant medium of water, preferred closure concepts were developed for the 20 ft. , 40 ft. , and 60 ft. diameter concrete cylinders.

For the 20 ft. diameter cylinder, an oversized steel sphere with an opening equal to the cylinders' diameter is the recommended end-closure . The sphere, similar to a ball-valve, is mounted on trunnions, and may be rotated to provide either full access to the cylinder or completely seal the opening.

Closure weight does become significant when a 40 ft. diameter cylinder is considered. In this case the flat steel bulkhead is recommended because its geometry permits a rolling movement. The bulkhead is rolled on its edge on a prepared mat, away from the cylinder. The rolling motion is induced by shifting water between the bulkhead's internal compartments. In this manner, heavy lifts are avoided.

Because of the excessively large weight associated with any closure configuration for the 60 ft. diameter concrete cylinder, the preferred concept consists of floating a full spherical concrete shell closure from the cylinder while in shallow water and then transporting the cylinder to land. A light steel secondary closure is necessary to keep the cylinder water tight until it reaches land.

As a result of this study, it is concluded that, although closure structures of this size and weight are not common, design and construction is within the current state of technology. It is recommended however, that due to the conceptual nature of this study, further evaluation be undertaken including model design and testing.

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