Steel Buildings in Europe

Title APPENDIX D Worked Example: Design of portal frame using elastic analysis 13 of 44 4 - 94 Verification of spacing between intermediate restraints In this case the restraint to the tension flange is provided by the siderails. These siderails are spaced at 1900 mm. The limiting spacing as given by Annex BB of EN 1993-1-1 is: L m = 2 y t 2 pl,y 2 1 Ed z 235 756 1 57 , 4 1 38              f AI W C A N i EN 1993-1-1 Annex BB §BB.3.1.1 C 1 is a factor that accounts for the shape of the bending moment diagram. C 1 values for different shapes of bending moment diagrams can be found in Appendix C of this document. For a linear bending moment diagram, C 1 depends on the ratio of the minimum and the maximum bending moments in the segment being considered. The ratios of bending moments for the middle and bottom segments of the column (without considering the haunch) are as follows:  = 444 222 = 0,50  1 C = 1,31 Appendix C of this document  = 222 0 = 0  1 C = 1,77 1 C = 1,31 is the most onerous case and therefore this is the case that will be analysed. L m =   2 4 3 2 2 3 235 355 89,3 10 11600 10 2194 756 1,31 1 11600 168 10 57 , 4 1 38 43,1                    L m = 1584 mm Siderail spacing is 1900 mm > 1584 mm Therefore the normal design procedure must be adopted and advantage may not be taken of the restraints to the tension flange. 7.5.2. Whole column (5275 mm) Firstly the whole column is verified. If the flexural buckling, lateral torsional buckling and interaction checks are satisfied for the length of the whole column, no further restraints are required. Otherwise, intermediate torsional restraints will be introduced to the column, or the column size increased. Flexural buckling resistance about the minor axis, N b,z,Rd b h  200 500  2,5 t f  16 mm