Shear Design for steel beams
Shear Design for steel beams
(OP)
The AISC spec, Eq. G2-1 says
Vn= 0.6*Fy*Aw*Cv
What is the 0.6 factor for? Does it have something to do with the fact that maximum shear stress is 1.5 times greater than the average shear stress?
Vn= 0.6*Fy*Aw*Cv
What is the 0.6 factor for? Does it have something to do with the fact that maximum shear stress is 1.5 times greater than the average shear stress?






RE: Shear Design for steel beams
RE: Shear Design for steel beams
DaveAtkins
RE: Shear Design for steel beams
RE: Shear Design for steel beams
That is interesting. That is what my S&J text says (when shear is acting alone - which is typically pretty close to the case unless there is a moment connection). My other text mentioned what I stated above. I certainly trust S&J over the other text, but that then doesn't account for the increased max shear over the average shear stress. That coupled with the fact that phi and omega for shear is 1.0 is leaving me a little confused. What is used to account for the max shear stress being higher than the average if that 0.6 is really 1/(sqrt3) ?
RE: Shear Design for steel beams
For one, the difference between the maximum and average shear stress for a wide flange is much less than the 1.5 for rectangles. My Salmon and Johnson, 4th edition, has an example on page 392 showing the maximum shear stress on the wide flange in the example is 18.1 ksi. The average shear stress, using V/(d tw), is 16.0 ksi, a difference of 11.6%.
We do wind up with less factor of safety against shear than we normally have for other checks, for the three reasons mentioned:
1. Using the average shear stress.
2. Using 0.6 instead of 0.577.
3. Phi is 1 instead of 0.9.
RE: Shear Design for steel beams
RE: Shear Design for steel beams
If Fy is based on a uniaxial tensile test, using mohr's circle would show the shear stress = Fy/2
Unfortunately I don't have S&J right now, could someone please explain the 1/sqrt(3) reasoning.
Thanks
RE: Shear Design for steel beams
The area of steel used in the Vn calculation is the area of the web, Aw. The code assumes a uniform shear stress of 0.6Fy acting over the area of the web and ignores the flanges due to their relatively small stresses from VQ/It.
RE: Shear Design for steel beams