Area of a compression flange regarding d/Af
Area of a compression flange regarding d/Af
(OP)
I have a common combination section trolley beam. Its an S-beam with a channel riveted to the top flange. The unbraced length is large so I need to calculate Fb. I can use the radius of gyration with Equation F1-7 from the Manual of steel construction ASD 9th Edition to get Fb, however the value is only 13.3ksi. Does anyone know how to calculate the Area of the compression flange for this combination section so that I can use equation F1-8 from ASD?
Is it simply the area of the s-beam flange plus the cross section of the channel?
Is it simply the area of the s-beam flange plus the cross section of the channel?






RE: Area of a compression flange regarding d/Af
RE: Area of a compression flange regarding d/Af
RE: Area of a compression flange regarding d/Af
YOu may want to look into a stability textbook. I know that there is one out there that was edited by Galambos, et al. I do not have the reference in front of me. Perhaps you can lay your hands on one.
RE: Area of a compression flange regarding d/Af
If you assume that this built up section behaves as a single member, you can calculate the bending stresses using traditional mechanics and area properties.
Locate the neutral axis and calculate the moment of inertia and section modulus of the composite section. Use
f=my/i to compute the bending stresses and compare them to the allowable stress.
Good luck.
RE: Area of a compression flange regarding d/Af
The area of the compression flange consists of the area of the cap channel plus the area of the flange (ref. Gaylord and Gaylord, Second edition, Page 6-23).
A second reference is the AISC design Guide Number 7, in Appendix A, Table 2, their tabulated d/Af values; they did consider the area of the cap channel.
I have seen other references that use less than 100% of the cap channel area. It is my opinion that this is conservative.
I hope this helps.