Allowable bending stress
Allowable bending stress
(OP)
Hi
I need some help with calculating the maximum allowable bending stress for a mild steel flat bar (fy = 248MPa). Is there a method for calculating this or do I just use 0.66*fy? Does it matter whether bending is about minor or major axis?
Thanks
I need some help with calculating the maximum allowable bending stress for a mild steel flat bar (fy = 248MPa). Is there a method for calculating this or do I just use 0.66*fy? Does it matter whether bending is about minor or major axis?
Thanks





RE: Allowable bending stress
If this is a fatigue/alternating stress application then you'll need to check the loads against a Goodman or Soderberg diagram.
The direction you bend it will change your stress due to that load but not the allowable since steel is isotropic.
http://www.linkedin.com/in/gregtirevold
RE: Allowable bending stress
Some codes will limit stress based on the idea of reaching yield at extreme fibers or yielding the entire section before buckling becomes a potential failure mode - so yes, it may matter which axis the bending is about.
jt
RE: Allowable bending stress
RE: Allowable bending stress
RE: Allowable bending stress
RE: Allowable bending stress
RE: Allowable bending stress
I'm not sure what other specs to refer to regarding bolted/welded steel fabrication. The SAE, from what I have seen, has very little in the way to offer. I saw one link a member here posted for an out of print SAE handbook for off-highway equipment and I think they still have a magazine on the topic but that is all I'm familiar with. They may have more to offer but their price structure isn't really friendly for small companies to "browse".
What would you recommend he use? I'm always up for new reading material.
http://www.linkedin.com/in/gregtirevold
RE: Allowable bending stress
RE: Allowable bending stress
If you can apply it to your design or industry great use it (good reference). Some times I can use the AISC code, some times I can't. Different codes may govern the assembly. A different SF might be selected that applies to the uncertainty of materials, loading, calculations, material strengths, duty, or manufacture quality.
ht
Cheers
RE: Allowable bending stress
The AISC code in question is a free download. The way the code is written, it is very convenient to adjust the factor of safety if the application requires it as well.
RE: Allowable bending stress
Thanks again
RE: Allowable bending stress
One way of looking at this is as a 'safety' factor. 0.66fy without any additional load factor is the same as a safety factor of 1.5. So decide what safety factor you require and work to that, for all the stresses in your design.
I am doing a similar project (luggage rack) and will be looking for a load factor of 3 or 4 times the anticipated working load to account for my lack of fabrication skill and any other unknowns. If I were making a fairing bracket I might design against a utilisation factor of nearly 1 on yield depending on the consequences of any failure.
RE: Allowable bending stress
0.66Fy is reasonable and acceptable for most building applications in the US.
The stress level will depend on the bending direction, as the section modulus of the flat bar changes with direction.