All purlins shall be designed in accordance with the requirements for uncased beams as specified in 8.2.1 and 8.2.2, and the limitations of bending stress based on lateral instability of the compression flange and the limiting deflection specified under 5.6.1 for the design of purlins. The maximum bending moment shall not exceed the values specified in 8.2.1. The calculated deflections should not exceed those permitted for the type of roof cladding used as specified in 5.6.1. In calculating the bending moment, advantage may be taken of the continuity of the purlin over supports. The bending about the two axes should be determined separately and checked according to the biaxial bending requirements specified in Section 9.
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