The Pratt type trusses of a factory building are spaced at 4.5 m c/c & purlins are spaced at 1.4 m c/c. The pitch of the truss is ¼ & the span of the truss is 10 m. The wind load on the truss normal to the roof is $1200 N/m^2$(suction), the dead load due roofing sheets purlins may be taken as $400 N/m^2$ and the live load may be taken as per I.S 875 (part-II).

(a) Design principal rafter of the truss and the main tie for the critical load combination as per IS800-2007.

(b) Write step by step procedure to design wind load as per IS 875(part-III)