Column Design Questions

[paulpatrick]

Euler or Johnson..?

The columns are short about .6m to 0.9m

I am inclined to use Johnson from what I was taught at college. when comparing the slenderness ratio with the column constant they both come out saying use Johnson.
Any structural guys out there have a good argument about each?

The Bloke at work is recommending the use of Euler.


Next you use the above to get and Critical stress.

Adjust the above by a factor of safety .

The you get the maximum stress as a result of bending at the the section location of interest.
If the maximum stress is less than the critical stress times the safety factor that means it ok Right?
Other wise you design may be subject to fail....Is my thinking flawed memory is a tad hazzy but this is the stuff I went to college for..ten years of just doing cad and what ever to pay bills and now been asked the right questions .
So I need some reminding please..

I have about 300 x 50 tonne loads to do. The stands are being transported from overseas to hold the load at sea. So bending moments must be taken in as well as static loads I am trying to use Box section mostly to but I have to use RHS too.

The blokes at work will be checking it!!

 

[ishvaaag]

So it seems you have some short columns part of stands that have to sustain containers or whatever the load in the sea, at ships,or maybe planes. This is a somewhat different environment than structural design for buildings, particularly in the effects of marine impact for ships, high g's environment in planes, fatigue, and then the ordinary considerations for material and geometrical nonlinearities.

I would look for some code that defines how to deal with the named (unusual for a "on earth" designer) solicitations. It may turn that for naval shipment just higher safety factors are used and the same procedures than on shore. One quick way to get it may be politely asking your senior structural designer, they should have made that kind of work before. Or just some naval -or aeronautical- engineer out there.

 

[csd72]

paulpatrick,

The basic theories that you talk about are not design codes and can be (in the case of euler) as much as 60% out. I am not familiar with the johnson method but I would not expect much greater accuracy.

It is also important to note that depending on the configuration, the effective length could be as much as double (or more) the actual length.

 

[BAretired]

Elastic buckling (Euler buckling) applies to slender columns. Inelastic buckling applies to intermediate columns. Short columns do not buckle...they fail axially at yield stress. If your columns are only 600 or 900mm long, they are not likely to be governed by Euler buckling.

You should decide which code applies to your work and follow the recommendations contained in it.

BA

 

[msquared48]

Depending on the section used, and the kl/r, they may not be short columns, but probably are.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask