Steel Buildings in Europe

Title APPENDIX D Worked Example: Design of portal frame using elastic analysis 40 of 44 4 - 121 In this case, all cross-sections have been treated as Class 3, and therefore the elastic properties have been used. This is conservative. However, from previous calculations carried out to check the rafter, it is observed that cross-section No.1 is Class 1. It may be that other sections between cross-sections No.1 and No.5 are plastic sections and therefore a greater moment resistance could be achieved. Table 5 Bending verification for cross-sections 1 to 5 Cross- section (i) M Ed (kNm) W el,min (mm 3 )  10 3 M el,Rd (kNm) M Ed  M el,Rd 1 661 4055 1440 Yes 2 562 3348 1189 Yes 3 471 2685 953 Yes 4 383 2074 736 Yes 5 298 1500 533 Yes 8.3. Buckling resistance There is a torsional restraint at each end of the haunched length. 298 kNm 661 kNm 471 kNm 2740 mm Buckling length considered When the tension flange is restrained at discreet points between the torsional restraints and the spacing between the restraints to the tension flange is small enough, advantage may be taken of this situation. In order to determine whether or not the spacing between restraints is small enough, Annex BB of EN 1993-1-1 provides an expression to calculate the maximum spacing. If the actual spacing between restraints is smaller than this calculated value, then the methods given in Appendix C of this document may be used to calculate the elastic critical force and the critical moment of the section. On the contrary, if the spacing between restraints is larger than the calculated value, an equivalent T-section may be used to check the stability of the haunch.