API BULL 2U-2004 pdf download.Bulletin on Stability Design of Cylindrical Shells.
effective length factor (K) : The ratio between the effective length and the unbraced length of the member. effective section : Stiffener together with the effective width of shell acting with the stiffener. effective width : The reduced width of shell or plate which, with an assumed uniform stress distribution, produces the same effect on the behavior of a structural member as the actual width of shell or plate with its nonuniform stress distribution. elastic buckling stress : The buckling stress of a cylinder based upon elastic behavior. general instability : Buckling of one or more circumferential (i.e., ring) stiffeners with the attached shell plate in ring-stiffened cylindrical shells. For a ring- and stringer-stiffened cylindrical shell general instability refers to the buckling of one or more rings and stringers with the attached shell plate. hierarchical order of instability : Refers to a design method that will ensure development of a design with the most critical instability mode (i.e., general instability) having a higher critical buckling stress than the less critical instability mode (i.e., local instability). hydrostatic pressure : Uniform external pressure on the sides and ends of a member. inelastic buckling stress : The buckling stress of a cylinder which exceeds the elastic stress limit of the member material. The inelastic material properties are accounted for, including effects of residual stresses due to forming and welding. interaction of instability modes : Critical buckling stress determined for one instability mode may be affected (i.e., reduced) by another instability mode. Elastic buckling stresses for two or more instability modes should be kept apart to preclude an interaction between instability modes. local instability : Buckling of the shell plate between the stiffeners with the stiffeners (i.e., rings or rings and stringers) remaining intact. membrane stresses : The in-plane stresses in the shell; longitudinal, circumferential or shear.
1.1 SCOPE 1.1.1 This Bulletin provides stability criteria for determining the structural adequacy against buckling of large diameter circular cylindrical members when subjected to axial load, bending, shear and external pressure acting independently or in combination. The cylinders may be unstiffened, longitudinally stiffened, ring stiffened or stiffened with both longitudinal and ring stiffeners. Research and development work leading to the preparation and issue of all three editions of this Bulletin is documented in References 1 through 16 and the Commentary. 1.1.2 The buckling capacities of the cylinders are based on linear bifurcation (classical) analyses reduced by capacity reduction factors which account for the effects of imperfections and nonlinearity in geometry and boundary conditions and by plasticity reduction factors which account for nonlinearity in material properties. The reduction factors were determined from tests conducted on fabricated steel cylinders. The plasticity reduction factors include the effects of residual stresses resulting from the fabrication process. 1.1.3 Fabricated cylinders are produced by butt-welding together cold or hot formed plate materials. Long fabricated cylinders are generally made by butt-welding together a series of short sections, commonly referred to as cans, with the longitudinal welds rotated between the cans. Long fabricated cylinders generally have D/t ratios less than 300 and are covered by AP RP 2A. 1.2 LIMITATIONS 1.2.1 The criteria given are for stiffened cylinders with uniform thickness between ring stiffeners or for unstiffened cylinders of uniform thickness. All shell penetrations must be properly reinforced. The results of experimental studies on buckling of shells with reinforced openings and some design guidance are given in Ref. 2. 1.2.4 Failure due to material fracture or fatigue and failure caused by dents resulting from accidental loads are not considered in the bulletin. 1.3 STRESS COMPONENTS FOR STABILITY ANALYSIS AND DESIGN The internal stress field which controls the buckling of a cylindrical shell consists of the longitudinal membrane, circumferential membrane and in-plane shear stresses. The stresses resulting from a dynamic analysis should be treated as equivalent static stresses. 1.4 STRUCTURAL SHAPEAND PLATE SPECIFICATIONS Unless otherwise specified by the designer, structural shapes and plates should conform to one of the specifications listed in Table 8.1.4-1/2 of API RP 2A, 20th edition, or Table 4 of API RP 2T. 1.5 HIERARCHICAL ORDER AND INTERATCTIONOF BUCKLING MODES 1.5.1 This Bulletin requires avoidance of failure in any mode, and recommends sizing of the cylindrical shell plate and the arrangement and sizing of the stiffeners to ensure that the buckling stress for the most critical general instability is higher than the less critical local instability buckling stress.