7.18 require a higher degree of alignment than is necessary for an individual hull. The analysis is complicated by the interaction of the hulls and the bulkheads due to the differential radial expansion of the inner and the outer hulls after pressurization and spin-up (see Section VII.4.4). A major benefit, however, is the fact that the bulkhead-hull assembly forms a large "box beam" structure which makes the hull resistant to bending and torsional loads (see Appendix VII.BJ. This compartmentalized hull leads to several major assembly decisions, the first of which is the determination of the compartment size. The size was chosen as a convenience, not too small as to require an excessive amount of material and assembly time and not too large as to negate the safety aspect of the compartments by making the inner hull plate too large to take the pressure differential 'resulting from a failure in the outer hull (see Sections VII.2 and VII.4). The size settled on is a 12° circumferential arc (20.9m at the inner hull and 21.99m at the outer hull) and five axial sections in the cylindrical portion of the hull to make the length 20m and to have the compartments take the shape of squares. The compartments in the endcaps remain~ 20 meters in length but their width narrows as the apex of the endcap is approached. The axial bulkheads remain as continuous units along the entire colony length and follow "great circles" on the endcaps (see Figures 7.5 and 7.6). This eliminates the problem of terminating the load of one bulkhead into the middle of a transverse bulkhead. The assembly procedure (see Sections VIII.5 and VIII.7) calls for the welding of relatively small panels into 20m x 20m hull sections and 20m x Sm bulkhead sections, and the attachment of these sections by fasteners to the hull (see Figure 7.7). This fastening of major panels and bulkheads allows a relaxation of the assembly tolerances and provides a means for physically separating hull panels to prevent cracks from propagating from one compartment to an adjacent compartment. Finally, the compartmentalized hull leads to a simple inspection technique. For further details concerning inspection and repair of the completed hull see Chapter VIII.
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