4. An A36 light gage cold-formed steel channel (C9X20) used as purlins are simply supported on roof trusses at 3m apart. Sag rods are placed at midspan of the purlins. Assume the purlins to be a compact section and that all the loads are acting at the centroid of the purlins. Use LRFD method and Co = 1.30. Given: Slope of the top chord of the truss: 14 degrees Purlin spacing: 1m Dead load (including self-weight): 2kPa Live load: 2.5kPa Wind load: 1.5kPa Windward coefficient: 0.20 Its = 21.6 U = 1.2DL + 1.6LL + 0.5W Sx = 221.23x10 mm S, = 19x103 mm Zx = 258.92x103 mm Z, = 38.51x103 mm Determine the following: Design flexural strength about x-axis (15pts) Design flexural strength about y-axis (5pts) Factored moment about x-axis (10pts) Factored moment about y-axis (5pts) Interaction ratio (5pts) . . . For this problem only, compute rusing approximate fomula instead of the exact one. 4. An A36 light gage cold-formed steel channel (C9X20) used as purlins are simply supported on roof trusses at 3m apart. Sag rods are placed at midspan of the purlins. Assume the purlins to be a compact section and that all the loads are acting at the centroid of the purlins. Use LRFD method and Co = 1.30. Given: Slope of the top chord of the truss: 14 degrees Purlin spacing: 1m Dead load (including self-weight): 2kPa Live load: 2.5kPa Wind load: 1.5kPa Windward coefficient: 0.20 Its = 21.6 U = 1.2DL + 1.6LL + 0.5W Sx = 221.23x10 mm S, = 19x103 mm Zx = 258.92x103 mm Z, = 38.51x103 mm Determine the following: Design flexural strength about x-axis (15pts) Design flexural strength about y-axis (5pts) Factored moment about x-axis (10pts) Factored moment about y-axis (5pts) Interaction ratio (5pts) . . . For this problem only, compute rusing approximate fomula instead of the exact one