Steel Buildings in Europe

Part 5: Detailed Design of Trusses 5 - 39 The slenderness is given by: 1,085 2594 8600 0,355 ,    x N Af cr y y y  The buckling curve to use is curve b (see EN 1993-1-1, table 6.2), and the imperfection factor is: 0,34   ) 1,239 0,5 (1 ( 0,2) 2 z y y          Φ 0,544 1,239 1,085 1,239 1 1 2 2 2 2          y y y y   The design buckling resistance is: kN Af N M y y b y Rd 1661 1,0 8600 0,355 0,544 1 , ,        The buckling resistance in the plane of the truss is less and the verification is: 0,541 1,0 1154 624,4 b,Rd Ed    N N OK The resistance of the diagonal is adequate; its section could be optimised. Connection battens The diagonal is composed of two angles linked by battens. The calculation of the resistance previously undertaken assumed the section is homogenous (for the buckling out of plane of the truss). In order to support this hypothesis, EN 1993-1-1 requires the placing of connection bars spread out at no more than 15 times the minimum radius of gyration of the isolated angle;, for an angle 150 × 150 × 15 that is a distance of 15 × 29,3 = 440 mm. In view of the resistance reserves, it is recommended that the connection bars be spaced further apart (the costs of fabrication and installation are not negligible). Instead of the 12 connection battens per diagonal which the above condition lead to, consider only 3 bars be placed, 1366 mm apart. L 150x150x15 Plate 150x150x10 and 2 pre-tensioned bolts with controlled tightening Figure 4.4 Connection batten In order for the battens to be effective, they must be arranged as illustrated here. This results in a buckling length about the principal axis equal to 0,7 × 1366 = 956 mm.