D8.A.2.6 Bending
The design bending moment capacity of a section is primarily dependent on whether the member is laterally supported or unsupported.
You can control the lateral support condition of the member by the use of
LAT
parameter. The type of member (i.e., cantilever, simply supported,
or general) is specified using the CAN
parameter.
If the member is laterally supported, then the design strength is calculated as per the provisions of the section 8.2.1 of IS 800:2007, based on the following factors:
- Whether section with webs susceptible to shear buckling before yielding
- Ratio of shear force to design shear strength
- Section classification
If the member is laterally unsupported, then the design strength is calculated as per the provisions of the section 8.2.2 of IS 800:2007, based on the following factors:
- Lateral Torsional Buckling
- Section Classification
Laterally unsupported sections of a solid rod are considered as laterally supported as mentioned in Cl. 8.2.2(b). The plastic moment of inertia, Zp , is calculated as D3/6.
Working Stress Design
Actual bending stress values are given by, about major (Z) and minor (Y) axes, respectively:
The permissible bending stress is given as follows:
-
For laterally supported beams:
- Fabc = Fabt = 0.66·Fy for Plastic or Compact sections
- Fabc = Fabt = 0.60·Fy for Semi-compact sections
-
For laterally unsupported beams:
-
About the major axis:
fabcz = 0.60·Md/Zeczfabtz = 0.60·Md/Zetz -
About the minor axis, the permissible bending stress is calculated as for a laterally supported section.
-
Slender Sections
For member with slender section subjected to bending, moment is taken by flanges alone. Design bending strength should be calculated with effective elastic modulus disregarding the contribution of web of the section.
Where:
The Moment Capacity will be Md = Ze· fy/γm0
for Laterally Supported
condition.
The Moment Capacity will be Md = Ze· fbd/γm0
for Laterally Un-Supported
condition.
Where, fbd is defined in clause 8.2.2 of IS:800-2007 (described in previous Working Stress Design section).