what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
(OP)
from aisc 9th edition 0.6fy or 0.66fy. does asme have different formula?
I'm lifting a pipe and wants to know the maximum unsupported length and maximum cantilever length.
pipe is just self weight. i can calculate the maximum moment and section modulus of pipe.
I just need the capacity formula to compare it to. also deflection is not an issue during lifting as long as deflection is elastic.
I'm lifting a pipe and wants to know the maximum unsupported length and maximum cantilever length.
pipe is just self weight. i can calculate the maximum moment and section modulus of pipe.
I just need the capacity formula to compare it to. also deflection is not an issue during lifting as long as deflection is elastic.






RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
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RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
tolerances will work against you all of the wrong ways:
You need to do the math, but you must:
-use the maximum allowed wall thickness when figuring the weight per unit length. Gives you highest weight.
-use the minimum allowed wall thickness when figuring the buckling stress at the most critical position (the point of buckling starting) which gives you the minimum expected strength to resist the buckling
-use the minimum allowable metal strength
But try both the minimum and the maximum allowed diameter at the point of buckling: I'm not sure which is more likely to fail.
Also, assume a point load at the hook - as if all the weight were at the bottom of the pipe at single point. If you ALWAYS use a sling or a support to spread the load out below the hook, then you could assume a linear load the length of the lifting clamp.
I say buckling (not long radius bending) because your failure will happen when the pipe kinks, not when it sags. Or when the pipe sags so much you cannot lift the middle high enough to pick both ends up off the floor. (For example, in a 20 foot high building with a 16 foot crane height, you cannot lift a 120 foot long string of pipe high enough to get it out the door.)
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
Moment max = 446 kip-in, Sx of pipe = 984.73 in3
stress = 0.45ksi
even at 0.3 fy = 0.3*35 = 10.5ksi
am I missing something here? since I'm neglecting deflection, 15' even 20' cantilever is more than ok
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
Bucking is more for compression, not flexure. Althogh there are flexure limits on AISC due to local buckling of flanges.
Not sure what it says about round shapes.and its local buckling of wall.
15' cantilever doesn't seem crazy to me for a 3.5' diameter pipe.
T
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
Local Buckling in flexure for that pipe is not applicable as it is a compact section. In more slender members local buckling can start to control flexure strength.
I show the nominal flexural strength of that pipe to be 3722.6 kip-ft via formula F8-1 and an assumed Fy of 35 ksi.
That pipe can easily cantilever 15' under self weight. I've seen 80' long sections of pipe choked with two straps about 10' apart in the middle and the deflection is hardly perceptible.
You'll also find that the code tables using these formulae (like 3-13 for square tubes) reduce all the allowable stresses by 7% due to specification tolerance and mills that are really good at hitting the bottom end of the spec. Take that for what it's worth in your application.
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
But not in this case. If you pick up a very long hollow member by the middle, the very long flexible member (the pipe obviously) WILL bend down on both ends with the highest stress where the crane hook (chain or cable) is wrapped around the pipe. the middle of the pipe goes up as the crane lifts, the ends sag down (and slide towards the middle) until the the whole pipe is lifted off of the ground.
But if the "pipe" (or hollow tubing, or sheet metal gutter, or 1/4 tubing, or 40 foot length of poly) is too flimsy (has too small a S value) then the middle of the pipe buckles as the shape collapses. Zero axial load, but only bending load at the sharp-edged lifting point.
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic
RE: what is the maximum allowable bending stress formula for pipe? deformation needs to be elastic