Hi Richard and all members,

I have a model successfully run and all are within allowable code stresses. I changed the insulation density field with a reduction of 20% all throughout the system. I anticipated that the result would yield lower stresses and of course lower loads on the restraint summaries. The actual result however showed failure on SUS+F1+F4. restraint summay however showed a lesser figure as I expected. What I was doing was saving my original file with a higher insulation density to a new file name. I then change the insulation density of the new file in spread sheet and run it. Is this due to load cases setup? I can send the whole load case combination if needed. So far the one I mentioned is the only one failing. Please advice.

Art Dieter
New Member

If you use the "\File\Save As" option, your load case setup is also copied to the new job name.

The first thing to do here is to compare the two "center of gravity reports" presented by the Error Checker.

Thanks Richard,

Yes I did it and obviously I found the problem too. It is the right mechanics. The heavier the insulation, or saying it the other way, the higher the SUS weight the better against Forces. Thanks.

Richard,

Just on the process of learning this job and reading the code, studying frommte forum too I think the code required load with sustained are wind, seismic, snow only ex. SUS+H+U1/U2 OR ...+WIN1/WIN2 etc. Am I right? Is SUS+F1+F4 code requirement? Thank you for the help.

For the evaluation of primary, force based, collapse loads, the B31.1/B31.3 codes require:

1) A Sustained case evaluation, which would consist of force based load primatives such as Weight, and Pressure.

2) An Occasional case evaluation. What the codes say is that the "stresses" from the occasional loads are to be summed with the stresses from the Sustained loads.

As to your questions:

1) Does the code want you to evaluate SUS + Wind (or seismic, or snow)? Yes. Be careful how you setup your Occasional load cases to properly account for non-linear restraints. Here is the correct way to set things up.<table border="1"><tr><th>Case</th><th>Components</th><th>Stress Type</th><th>Comment</th></tr>
<tr><td>1</td><td>W+P1+T1</td><td>OPE</td><td>Typical operating case</td></tr>
<tr><td>2</td><td>W+P1</td><td>SUS</td><td>Typical sustained case</td></tr>
<tr><td>3</td><td>W+P1+T1+U1</td><td>OPE</td><td>Operating case including occasional event</td></tr>
<tr><td>4</td><td>L1-L2</td> <td>EXP</td><td>Typical expansion case</td></tr>
<tr><td>5</td><td>L3-L1</td> <td>OCC</td><td>Construction case to obtain the occasional
stresses. This is not a code case.</td></tr>
<tr><td>6</td><td>L5+L2</td> <td>OCC</td><td>Occasional case for code compliance.</td></tr>
</table>

You can't simply setup case 3 (above) as U1 and then sum L2+L3 (or setup W+P1+U1) because the non-linear restraints won't be in their operating position.

2) Is SUS + F1 a code requirement? Maybe, it depends on what F1 is. If F1 represents are part of the system, say a valve hand wheel, I would suggest you model this as a rigid element with the appropriate weight, then this weight will be part of "W" and you won't need F1. If F1 represents a load, then does it act all the time or only some time? If it acts all the time then this load primative should be part of the Sustained load case. If it acts some of the time (like a relief thrust load) then it is a component of an Occasional load case.

Thank you very much Richard,

Yes, we are required to comply wind and seismic. Also that F1 & F4 represent relief thrust load and I was made to consider it OCC. Thank you so much for the load case above. I am very pleased all the time how much we could learn thru all your supports and the expert members. I maybe attending seminar most likely this coming year on static and dynamic there in Houston. Thanks again Richard.