Steel Buildings in Europe

Title APPENDIX D Worked Example: Design of portal frame using elastic analysis 4 of 44 4 - 85 3.4. Load combinations For simplicity, the wind actions are not considered in this example. Therefore, the critical design combination for choosing the member size is:  G G +  Q Q Where: Q is the maximum of the snow load and the imposed load.  G = 1,35 (permanent actions)  Q = 1,50 (variable actions) EN 1990 The snow loads are greater than the imposed loads on the roof, therefore Q = 4,45 kN/m 4. Preliminary sizing Single-storey steel buildings. Part 2: Concept design [2] provides a table of preliminary member sizes, according to the rafter load and the height to eaves. Rafter load = 1,35( 2,16 + self weight )+1,5  4,45 = 9,6 kN/m + self weight Say 10 kN/m to include self weight. The section chosen for the rafter is an IPE 450, S355 The section chosen for the column is an IPE 500, S355 5. Buckling amplification factor  cr In order to evaluate the sensitivity of the frame to 2 nd order effects, the buckling amplification factor,  cr , has to be calculated. This calculation requires the deflections of the frame to be known under a given load combination. EN 1993-1-1 §5.2.1 An elastic analysis is performed to calculate the reactions under vertical loads at ULS, which provides the following information: The vertical reaction at each base: V Ed = 168 kN The horizontal reaction at each base: H Ed = 116 kN The maximum axial force in the rafters: N R,Ed = 130 kN 5.1. Axial compression in the rafter According to the code, if the axial compression in the rafter is significant then  cr is not applicable. In such situations, Appendix B of this document recommends the use of  cr,est instead. The axial compression is significant if Ed y 0,3 N Af   or if N Ed  0,09 N cr , which is an equivalent expression. EN 1993-1-1 §5.2.1(4) Note 2B N Ed is the design axial load at ULS in the rafter, noted N R,Ed in this example.