Stress Combination
Stress Combination
(OP)
Here is something I have been arguing with another engineer about and wanted to what others say. It is a simple question: If you have a horizontal force and vertical force acting at the same time on a beam how the stresses should be added? I am saying that the stresses should be simply superimposed (regardless of the shape) but his thoughts were that the resultant force (sq. root of sum of sq’s) should be used to calculate the max. stress. Any thoughts?
Thanks in advance.
Thanks in advance.






RE: Stress Combination
RE: Stress Combination
corus
RE: Stress Combination
I would do P/A +or- M/S, making sure to account for any eccentricity of the horizontal (axial)load (if it exists.
RE: Stress Combination
RE: Stress Combination
RE: Stress Combination
For connection, you have to consider the combined effect of both.
For Beams, these forces will create shear and bending, so should handle as per code.
For columns, as structuralEIT has mentioned.
For other members, use your judgement.
RE: Stress Combination
Given the axial load, you could also take the secondary moment of the internal axial force times the deflection at that point, but this may not be necessary for what you are doing and also would affect both of your approaches the same way.
I still say you will get the same answer with both approaches.
RE: Stress Combination
the advantage that a vector load would have would be bending of an odd shaped section, where the load has to be resolved onto the principal axes for bending; with components you'd have to do this twice.
RE: Stress Combination
can you please elaborate? I am not seeing your point. If I were given a beam-column to analyze and it had a single load on it at some angle (theta), the very first this I would do is resolve this load into the vertical and horizontal components (or a load along the axis of the member and perpendicular to the axis of the member), then construct a shear and moment diagram.
I am not following you. How would you approach this seemingly VERY simple analysis?
RE: Stress Combination
RE: Stress Combination
Where it wont work is circular sections(or pipes) these would have the maximum stresse at different points. You should always get the resulant moment for circular members.
The one drawback with getting the resultant is that you dont get the benefit of the larger allowable stress around the minor axis. Also how do you calculate for buckling?
All the code clauses are based on major and minor axis treated separate.
csd
RE: Stress Combination
RE: Stress Combination
The reason I have mentioned code is because, for beams, per code the shear and bending can be handled seperately. Even though the resultant combination of these two will be more than the indivisual stress.
RE: Stress Combination
could your collegue mean that it is more conservative to apply the vector, and so "better" ?
RE: Stress Combination
the resulting stresses Bending and torsional are almost the SAME !
RE: Stress Combination
RE: Stress Combination
There is no combining of shear and normal stresses for a steel beam using the AISC code.
Re: Sections F4 and H1 of AISC 9th Ed.
RE: Stress Combination
The combined stress for an I shape, incidentally, is not the sq. root of sum of sq’s., but the sum of the stresses, i.e., ftotal=fa+fb.
I agree that a round shapes and those with axial force are handled differently, but I don't think that's what the OP had in mind.
RE: Stress Combination
RE: Stress Combination
I didn't mean to take issue with your post. In fact, I totally agree (Notice, I was in the 8th edition, as I'm at home). I was trying to clarify the issue for those who seemed to understand the OP differently than I did.
RE: Stress Combination
RE: Stress Combination
i took the sqrt of the sum of squares to refer to the vector addition (not the stress combination)