Load Combination, Limit Load Analysis

[Doodler3D]

Hi,

For a work bin experiencing mild vacuum and a valve at its lower end, I have two loads:

1. Vacuum (P)
2. Valve weight on lower end (D)

Is that a load combination of: 1.5*P and 1.5*D based on table 5.4 for a limit load analysis (5.2.3 of the ASME BPVC Sec VIII Div 2 code)?

If the bin is filled with material, I will have to include 1.5*P, 1.5*D and 1.7*L?(transient material loading)

Thank you

 

[TGS4]

That seems reasonable.

With your vacuum condition, you will have compressive stresses. So, don't forget to complete the analysis with a buckling analysis per 5.4.

 

[Doodler3D]

@TGS4 Thank you. Is a mechanical engineer allowed to perform ASCE 7-16 calculations for wind and seismic loading after prerequisite training?

 

[TGS4]

Is a mechanical engineer allowed to perform ASCE 7-16 calculations for wind and seismic loading after prerequisite training?

I am not aware of any restrictions in this regard.

 

[saplanti]

Isn't this part of the ducting for material handling?

Why do you consider to use a pressure vessel code to design this structure?

Why cannot use a structural design code or one of the ducting design code?

 

[Doodler3D]

saplanti, yes material handling but not ducting.

Clients have unrealistic demands and the cost of steel is making it harder. ASME/FFS elastic-plastic method seems to do the job. I'm still learning, so this is only a practice task.

 

[saplanti]

In case this is a chute or a feeder you need to provide us pressures are occurred with an adequate diagram. I believe the suction that you talk about is not a full suction. Solving this kind of application by the pressure vessel code will be highly costly, first analysis and second manufacture. Mostly, these are not the subject of the pressure vessel codes. Check the applicability for pressure and temperature in the code.

Please tell us the demand of your client. I guess they are looking for a resistance to abrasive wear the most, and you may have to use the suitable steel with adequate strength. Providing some stiffeners outside might solve the suction, and perhaps the internal pressure requirements. Do you think a suction/pressure pulses are available in the system? If so you need stiffness which may be provided by the stiffeners again.

I think today most of the designers want to use FEA programs for this kind of applications. I believe it is waste of time for many cases.

 

[Doodler3D]

Saplanti,

Jobs have been sent outside for analysis by structural engineers, and separately to analysts who did a full FEA analysis in addition to testing. Elastic-plastic (ASME FFS-1) was way cheaper and aligned with the test results. This particular job is only training. I have a year at least, till I am able to make engineering design decisions.