A W section steel purlin span 6.7 m between roof trusses on centers. The roof is assumed to support a dead load of 880 N/m2 of roof surface including self-weight and a live load of 816 N/m2 of horizontal roof surface projection. The slope of the roof truss is 1 vertical to 2 horizontal and the purlins are spaced 1 m on centers. Use A36 with Fy = 248 MPa. Assume all loads pass through the center of gravity of the section. Sag rods are to be placed at the middle thirds between trusses. Determine the ratio of the actual to the allowable bending stress. DO NOT ROUND-OFF DURING THE COURSE OF SOLVING. ANSWER IN FOUR DECIMAL PLACES. Properties of W Section A = 2,887 mm2 d = 192.5 mm bf = 100.7 mm tf = 10.82 mm Sx = 174,900 mm3 Sy = 36,133 mm3 tw = 6.1 mm Use the following allowable stresses (NSCP 2001): For bending about strong axis, Fbx=0.66 Fy For bending about weak axis, Fby=0.75Fy
A W section steel purlin span 6.7 m between roof trusses on centers. The roof is assumed to support a dead load of 880 N/m2 of roof surface including self-weight and a live load of 816 N/m2 of horizontal roof surface projection. The slope of the roof truss is 1 vertical to 2 horizontal and the purlins are spaced 1 m on centers. Use A36 with Fy = 248 MPa. Assume all loads pass through the center of gravity of the section. Sag rods are to be placed at the middle thirds between trusses. Determine the ratio of the actual to the allowable bending stress. DO NOT ROUND-OFF DURING THE COURSE OF SOLVING. ANSWER IN FOUR DECIMAL PLACES.
Properties of W Section
A = 2,887 mm2
d = 192.5 mm
bf = 100.7 mm
tf = 10.82 mm
Sx = 174,900 mm3
Sy = 36,133 mm3
tw = 6.1 mm
Use the following allowable stresses (NSCP 2001):
For bending about strong axis, Fbx=0.66 Fy
For bending about weak axis, Fby=0.75Fy
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