Question

Flexural strength design check of sections of a typical internal portal frame:

The load cases which you are expected to analyse for portal frame in this exercise, and from which the design bending moments and the coincident axial forces required for this section should be derived, are discussed in the ‘Supplementary Notes’. The moment capacities Msx and Mbx and the axial capacities Ns, Ncx and Ncy may be determined using the tables in the AISC ‘Design Capacity Tables for Structural Steel’ publication.

Rafters:
Check the flexural strength of the rafters in a typical internal portal frame, in the general vicinity of the ridge. Again, check for the two cases of maximum sagging B.M. at or near the ridge and maximum hogging B.M. at or near the ridge, and allow for the coincident axial force. Again, note that:
 The purlins in the roof are at 1250mm centres, generally.
 Assume there is fly bracing at the ridge and then at 4 spaces from the ridge (obtain value depending on frame geometry).
For the rafters assume Grade 300 steel.

Answer 1