D1.B.1.1.4 Bending Stress
Allowable bending stress for tension and compression for a symmetrical member loaded in the plane of its minor axis, as given in Section 1.5.1.4 is:
F_{b} = 0.66F_{y}
If meeting the requirements of this section of:
- b_{f}/2t_{f} ≤ 65/√(F_{y})
- b_{f}/t_{f} ≤ 190/√(F_{y})
- d/t ≤ 640(1 - 3.74 (f_{a}/F_{y}))/√(F_{y}) when (f_{a}/F_{y}) < 0.16, or than 257/√(F_{y}) if (f_{a}/F_{y}) > 0.16
- The laterally unsupported length shall not exceed 76.0 b_{f}/F_{y} (except for pipes or tubes), nor 20,000/(d F_{y}/A_{f})
- The diameter:thickness ratio of pipes shall not exceed 3,300/√(F_{y})
If for these symmetrical members, b_{f}/2t_{f} exceeds 65/√(F_{y}), but is less than 95/√(F_{y}), F_{b} = F_{v}(0.79 - 0.002(b_{f}/2t_{f})√(F_{y})
For other symmetrical members which do not meet the above, Fb is calculated as the larger value computed as per AISC formulas F1-6 or F1-7 and F1-8 as applicable, but not more than 0.60Fy. An unstiffened member subject to axial compression or compression due to bending is considered fully effective when the width-thickness ratio is not greater than the following:
- 76.0/√(F_{y}), for single angles or double angles with separators
- 95.0/√(F_{y}), for double angles in contact
- 127.0/√(F_{y}), for stems of tees
When the actual width-thickness ratio exceeds these values, the allowable stress is governed by B5 of the AISC code.
Tension and compression for the double symmetric (I & H) sections with b_{f}/2t_{f} less than 65/√(F_{y}) and bent about their minor axis, F_{b} = 0.75 F_{y} . If b_{f}/2t_{f} exceeds 65/√(F_{y}), but is less than 95/√(F_{y}), F_{b} = F_{y}(1.075 - 0.005(b_{f}/2t_{f})√(F_{y}).
For tubes, meeting the subparagraphs b and c of this Section, bent about the minor axis, F_{b} = 0.66F_{y} ; failing the subparagraphs B and C but with a width:thickness ration less than 238/√(F_{y}), F_{b} = 0.6F_{y} .