Section modulus of hollow section with a hole 3

[gasma1975]

Hi,

I have a hollow structure round section dia. 10''. I have to drill a hole 1'' on one side only, I need to know how it will affect the flexural resistance. How to calculate the section modulus ?

Thank you for helping

gasma1975

 

[structSU10]

You can calculate the new properties fairly easily, by using the full ciruclar section, and approximate the hole with a negative rectangular section. A really fast way is to draft it in AutoCAD and use massprop command. from that you can get I and the center of gravity, and calculate your S.

 

[gasma1975]

Thank you, I will try it...

 

[dhengr]

Gasma1975:
It staggers my imagination, that structural engineering has become such a rote process as to eliminate any need for thinking through the problem or for understanding how structures and members really work. Dig out your Strength of Materials ref. books and put your thinkin cap on, and try this approach on for size. Look up stress concentrations around a hole. Also, there are times when you do use the reduced, net area or net section, but this probably isn’t one of them. Do you go through this same process at every location and for every hole drilled or punched in a simple WF beam? You have a 10" o.d. pipe, of some reasonable wall thickness, and you want to drill a 1" hole someplace in one side, say btwn. 2 & 4 o’clock, right? Just for the heck of it, do the section property calcs. StructSU10 suggests, and report back, but the section props. shouldn’t change that much, nor should the gross section stresses. This is such a localized and small anomaly , that I would use the whole section props. and then ask the question, ‘what are the stress concentration effects in the region of the drilled hole, and what are the gross stress levels?’ This might be a different story if the drilled hole was larger and at 12 or 6 o’clock, and at the max. moment location; or if you were drilling an 8" dia. hole, leaving you a round open section, channel (C) type shape. And, it might be a different story if there were a whole line of closely spaced 1" holes. Pipe sections are not particularly efficient bending sections because of the lack of material in the max. normal bending stress regions. And, if they are thin walled or their dia. over thickness ratio (D/t) gets too large, they develop wall buckling and ovaling problems under high compressive stresses. For this you’ll want some more advanced ref. books.

 

[Ron]

Ditto dhengr. Well said.

You can drift as far as you want from the "basics" of engineering, but if you don't know the route to get back, you'll find yourself in deep do-do.

 

[a2mfk]

dhengr brings up a good point(s)- what is this pipe doing? It's a beam?