## Maximum beam stress calculation

## Maximum beam stress calculation

(OP)

I was wondering if anyone could tell me what is the standard for calculation the maximum stress on the outer fiber of a beam that is loaded laterally such that it has a beanding stress and a shear stress. My current understanding is that if the beam is short then the bending and shear stresses would need to be combined. I have been told that when these are combined, the aveage shear stress is combined with the maximum bending stress using Von Mises formula. If it is a wide flange section then only the web of the beam is considered when calculating the shear stress. When the web of the beam is considered, would the average shear stress (as opposes to the tranverse shear) on the web be combined with the max bending stress on the flange outer fiber?

How would the shear formula VQ/IT fit into the above analyses. Is it used in these calculations or only the average shear stress?

Thanks in advance,

How would the shear formula VQ/IT fit into the above analyses. Is it used in these calculations or only the average shear stress?

Thanks in advance,

## RE: Maximum beam stress calculation

## RE: Maximum beam stress calculation

Then the magnitude of the shear stress tau will follow a -if I remember well parabolical- law with a maximum at the center of the flanges -if we dismiss the web presence there, of course- and zero shear at the tips. This tau you evaluate by the equation you refer to, but remember that the static moment corresponds to the area beyond your ordinate in the direction of the load, and all data therein is for such direction of loading.

Bending Stress will follow the usual rule and for this direction will follow

sigma=My/(Iy/c)

By stating these laws as a function of c you may find a particular value of c at which the Von Mises comparison stress

sigmacomparison=SQRT(sigma^2+3·tau^2)

is at maximum.

This is easy to do in Mathcad or akin workspace, or you may chart for the combination.

But if you simply want to design a beam for these circumnstances you may check the on weak axis bending and corresponding shear by LRFD Chapter F, except it falls outside the specifications.

## RE: Maximum beam stress calculation

Thanks,

## RE: Maximum beam stress calculation

Yes use the von misses formula to determine resultant stress from bending and average shear stresses