Container Design

[engpes]

In analyzing DNV 2.7-1 containers, the primary load case assumed is a 2.5:1 load factor of the max gross rating of the container. Also, according to DNV 2.7-1 the allowable Von Mises stress is 85% of the yield stress (for steel).

I typically apply the ASD design method which, after code checks per H-1 & H-2, typically leads to my stresses maxing out at around 65% of the yield (roughly).

My question is this:

1.) Am I being overlly concervative by using the ASD method?

2.) Would the LRFD method by more realistic? Also is the 2.5:1 load factor a sufficient load case to apply this criteria as no load cases in ASCE really apply to a container.

Thanks in advance.

 

[truckdesigner]

I too have recently been involved in some Offshore Containers (never mind my user name).

To me a Von Mises stress of 85% is purely for guys analysing the frame in a 3D frame analysis software - that is a typical unit/readout.

I have a copy of some old school hand calculations that show a calculted bending stress of say 250 MPa as OK as it is less than 0.85 x 350 MPa (Grade 350 Steel).

I argue that that is incorrect as it is greater than 0.66 x Fy = 231 Mpa. (Australian Standard AS3990).

Am I correct?

Would be keen to get some opinions on this...

Regards.

 

[CTW]

You're probably being overly conservative using 0.66Fy. The 0.66Fy applied to ASD is used in conjunction with the load cases in AISC. If DNV recommends a load case of 2.5:1 with a allowable stress at 0.85Fy, this essentially results in a safety factor near 3. This is reasonable as it is in line with the safety factor on most lifting devices.

Since containers fall outside the scope of ASCE, you are correct using DNV 2.7-1 for the load factor.