M

h M Fd k ,\ b ht a h I 4Iā€ž "h k = ā€” h h b) Uplift loading

Figure 10.3: Conversion of torsion into lateral bending of the free flange

(5) The lateral bending moment MfL Sd should be taken as equal to zero if the free flange is in tension, otherwise MfetSd should be determined from:

Mt fe.Sd fz.Sd

where:

^0,fz.Sd's initial lateral bending moment in the free flange without any spring support; 0R is a correction factor for the effective spring support.

(6) The initial lateral bending moment in the free flange M0 iz Sd should be determined from table 10.1 for the critical locations in the span, at supports, at anti-sag bars and between anti-sag bars.

(7) The correction factor jSR for the relevant location and boundary conditions, should be determined from table 10.1, using the value of the coefficient R of the spring support given by:

KL 4

where:

/fz is the second moment of area of the gross cross-section of the free flange plus 1/6 of the web height, for bending about the z - z axis;

K is the lateral spring stiffness per unit length from 10.1.5.1;

La is the distance between anti-sag bars, or if none are present, the span L of the purlin. Table 10.1: Values of initial moment Mo fz Sd and correction factor /?R

/fz is the second moment of area of the gross cross-section of the free flange plus 1/6 of the web height, for bending about the z - z axis;

K is the lateral spring stiffness per unit length from 10.1.5.1;

La is the distance between anti-sag bars, or if none are present, the span L of the purlin. Table 10.1: Values of initial moment Mo fz Sd and correction factor /?R

System

Location

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