Combined Stress
Combined Stress
(OP)
I am analyzing an HSS Round section to determine combined stresses for evaluation of fatigue. The AASHTO Standards for Signs, Luminaires, and Signals 2009 is the governing code.
In several of the critical location the section experiences bending (multiple axes), axial compression, and shear (multiple axes). Could someone provide clarification on how these stresses can be combined? Is it simply addition or are square roots of the sum of the squares required? We recently had an office fire, which took my strengths of materials literature, so I could really use the help.
i.e.
fa + fvx + fvy + fbx + fby
fa + SQRT(fvx^2 + fvy^2) + SQRT(fbx^2 + fby^2)
or some other variation?
In several of the critical location the section experiences bending (multiple axes), axial compression, and shear (multiple axes). Could someone provide clarification on how these stresses can be combined? Is it simply addition or are square roots of the sum of the squares required? We recently had an office fire, which took my strengths of materials literature, so I could really use the help.
i.e.
fa + fvx + fvy + fbx + fby
fa + SQRT(fvx^2 + fvy^2) + SQRT(fbx^2 + fby^2)
or some other variation?






RE: Combined Stress
The steel manual covers this pretty well. See chapter H.
RE: Combined Stress
RE: Combined Stress
if you've got bending about two axes then the resultant normal stress is the sum of the normal stress from each moment.
RE: Combined Stress
The question originated from an attempt to meet constant amplitude fatigue limits (CAFL) set by AASHTO in the LTS Section 11.9. This section simply states a stress limit for a given detail category. In my case, I have a Category E Detail and the CAFL is 4.5 ksi.
Do fatigue stresses include shear and torsion stresses, or do they only include bending stress? If shear and torsion are included, how are these stresses to be combined?
Hope this clears things up a bit.
RE: Combined Stress
just my 2c