## Nqp

fyb^Mi f) Step 3: Repeat step 2 using reduced effective area ^ of stiffener As red from previous iteration, continuing until Xn « X(n - 1) but Xn ^ X(n - 1)

g) Adopt an effective cross-section with bx e2 , b2 c\ and reduced thickness r^ corresponding to xn

Iteration n

Figure 4.5: Compression resistance of a flange with an intermediate stiffener

(4) The reduction factor x may be taken as equal to 0,5 if:

otherwise the reduction factor x may be taken as approximately equal to 1,0 if:

where:

/s is the effective second moment of area of the stiffener, taken as that of its effective area As about the centroidal axis a - a of its effective cross-section, see figure 4.4.

(5) The reduced effective area of the stiffener As red allowing for flexural buckling should be taken as: ^s.red = xAs ... (4.28)

(6) In determining effective section properties, the reduced effective area As red should be represented by using a reduced thickness rred = x i for all the elements included in As.

(7) The effective section properties at serviceability limit states should be based on the design thickness t for all values of /s.

4.3.4 Trapezoidal sheeting profiles with intermediate stiffeners

### 4.3.4.1 General

(1) This sub-clause 4.3.4 should be used for trapezoidal profiled sheets, in association with 4.3.2 for flanges with intermediate flange stiffeners and 4.3.3 for webs with intermediate stiffeners.

(2) Interaction between the buckling of intermediate flange stiffeners and intermediate web stiffeners should also be taken into account using the method given in 4.3.4.4.

### 4.3.4.2 Flanges with intermediate stiffeners

(1) If it is subject to uniform compression, the effective cross-section of a flange with intermediate stiffeners should be assumed to consist of the reduced effective areas As re<j of up to two intermediate stiffeners and two strips of width 0,5freff adjacent to the edges supported by webs, see figure 4.6.

(2) For one central flange stiffener, the elastic critical buckling stress oCT should be obtained from: