Steel Buildings in Europe

Part 5: Detailed Design of Trusses 5 - 37 545 kN 470 kN Axial force N Ed Figure 4.3 Axial force in the lower chord 4.1.3 Diagonal in compression The diagonal, whose resistance is calculated here, by way of example, is the second diagonal from the right support (element B40 in Figure 3.1), under ULS gravity loading. The compression force is: N Ed = − 624,4 kN Initially, as in common practice, the bending moment due to the self weight of the member is ignored. The effect of this moment will be evaluated later. Cross-section properties of a single angle For a 150 × 150 × 15 L A = 43 cm 2 z G = y G = 4,25 cm I y = I z = 898,1 cm 4 I v = 369 cm 4 For a pair of angles Section area: A = 2 × 43 = 86 cm 2 Second moment of area out of plane of the truss (the section is assumed to be homogeneous), assuming the gap between the angles is 10 mm: I y = 2 × 898,1 + 2 × 43 × (4,25+1,0/2) 2 = 3737 cm 4 . Second moment of area in the plane of the truss: I z = 2 × 898,1 = 1796 cm 4 Class of section in uniform compression Material parameter for f y = 355 N/mm 2 :  = 0,81 For an angle (EN 1993-1-1 Table 5.2 (Sheet 3)): 10 11,5 9,31 2 15 2 150 2 10 15 12,15 15 150              t h b t h