s » 1 s a) single edge fold b) double edge fold Figure 4.2: Edge stiffeners
(1) The cross-section of an edge stiffener should be taken as comprising the effective portions of the stiffener, element c or elements c and d as shown in figure 4.2, plus the adjacent effective portion of the plane element b?.
(2) The procedure, which is illustrated in figure 4.3, should be carried out in steps as follows:
- Step 1: Obtain an initial effective cross-section for the stiffener using effective widths determined by assuming that the stiffener gives full restraint and that crcom ^ = /yb/7M1, see (3) to (5);
- Step 2: Use the initial effective cross-section of the stiffener to determine the reduction factor for flexural buckling, allowing for the effects of the continuous spring restraint, see (6) and (7);
- Step 3: Iterate to refine the value of the reduction factor for buckling of the stiffener, see (8) and (9).
(3) Initial values of the effective widths bel and Z?e2 shown in figure 4.2 should be determined from clause 4.2 by assuming that the plane element bp is doubly supported, see table 4.1.
(4) Initial values of the effective widths ceff and dQff shown in figure 4.2 should be obtained as follows:
a) for a single edge fold stiffener:
with p obtained from 4.2(4), except using a value of the buckling factor ka given by the following:
b) for a double edge fold stiffener:
with p obtained from 4.2(4) with a buckling factor ka for a doubly supported element from table 4.1;
with p obtained from 4.2(4) with a buckling factor ka for an outstand element from table 4.2.
(5) The effective cross-sectional area of the edge stiffener As should be obtained from:
(6) The elastic critical buckling stress acr s for an edge stiffener should be obtained from:
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