Allowable compressive stress due to bending
Allowable compressive stress due to bending
(OP)
Hi all,
The question may be silly, but what is the allowable compressive stress due to bending during lifting or shipping ?
Please refer to the attached sketch.
Still 2/3 of the yield like on the tensile side ? or any other formula ?
The question may be silly, but what is the allowable compressive stress due to bending during lifting or shipping ?
Please refer to the attached sketch.
Still 2/3 of the yield like on the tensile side ? or any other formula ?





RE: Allowable compressive stress due to bending
RE: Allowable compressive stress due to bending
The compressive stress in this case would be in the as-built thickness, ambient-temperature condition as well, which might increase it substantially.
I've seen data elsewhere to the effect that allowable compressive loading due to a moment could be considerably higher than compressive stress due to pure axial loading, and, if not required to be limited by the code, that might also allow some increase.
RE: Allowable compressive stress due to bending
Definitely take advantage of the as-built thickness and room temperature - buckling is based on the Young's Modulus as the sole material property.
RE: Allowable compressive stress due to bending
But look for the stress risers for likely places where the buckling will start. AND , yes, construction failures while lifting up "simple" walls from horizontal to vertical ARE a failure mode.
RE: Allowable compressive stress due to bending
RE: Allowable compressive stress due to bending
RE: Allowable compressive stress due to bending
Vessel can have many vacuum stiffing rings for external pressure. Does it means we can use “B” from UG23 and 28 to calculate the allowable buckling stress and treat it as the allowable compressive stress due to bending moment during lifting or transportation ? I wouldn’t think so.
In my sketch, the maximum compressive stress is close to 2/3 of the yield due to head heavy. If UG23 and 28 are a valid method, then I can simply add two stiffing ring between the maximum point, may be 1’ part, to make B exceeds compressive stress, or even I can define the small cone as line of support and make B large enough, and then I claim the maximum compressive stress is fine? Does not sound right.
The maximum compressive stress from bending moment will be very local at the farest point from the vessel center line. I do not think a gross buckling will occur even the compressive stress exceeds the “B” value from UG23 and UG28 if that can be calculated.
I could be wrong for all the thinking, but I am still not convinced the use of UG23 and 28.
RE: Allowable compressive stress due to bending
RE: Allowable compressive stress due to bending
Regards
r6155
RE: Allowable compressive stress due to bending
RE: Allowable compressive stress due to bending
"Vessel can have many vacuum stiffing rings for external pressure. Does it means we can use “B” from UG23 and 28 to calculate the allowable buckling stress and treat it as the allowable compressive stress due to bending moment during lifting or transportation ? I wouldn’t think so. "
In my view there is no problem with that as we are addressing the same failure mode (buckling) on both cases.
RE: Allowable compressive stress due to bending
In Dennis Moss 3rd edition page 389 (4th ed, page 664) for erection analysis, it says: " Compression (for short members only), allowable compressive stress = 1.33 x B. ". If that is true, that will save my vessel from any changes. Any opinion on that 33% increase on the B value ? And what is the "short members" the manual talking about ?
RE: Allowable compressive stress due to bending
Either way, get someone who actually understands buckling failure to assist you.