There was an instance when I was made to disregard the effect of seismic in an isolated platform 30 ft. high. I always thought that it is subject to uniform loads, the g factor being determined by UBC or lately IBC, needs occassional load cases with sustained loads. However I was told that the structure is not a building where infact I am used to (having in the past most piping system I analyzes inside the building). I am a bit confused but I think I need to include seismic in such platform.

Regards and thank you to everybody.

What code are you doing this work under???

Does the particular code require the consideration of the seismic G load??

Does the contract between the various parties require anything???

And finally your conciense tells you something is amiss hence your question.

Hi John,

Thanks for the reply. The project was for B31.1. Code requires it the way I undersderstand if the code say piping should be evaluated with occassional events, seismic, wind, etc. But I was stunned when I was argued that that structure was not a building. I used to prepare formal stress analysis report before and one page a bit more is always dedicated to the calculation of seismic "g" factor and our reference is of course UBC/IBC following their methodology for calculating this piping lateral loads. He said they have treated in the past steam boilers piping without occasional load simply because they are not classsified as buildings. My argument was: building are structure but not all structure are called building and I think wherever the pipe is, so long it is in seismic field it is always subject to acceleration load factor, g. I realized later they have problem with overstressing in some projects on occasional load cases.

The contract clearly stated piping has to be designed as per ASME B31.1.

Thanks John,

I quote from B31.1-2004

“101.5.3 Earthquake. The effect of earthquakes, where applicable shall be considered in the design of piping, piping supports, and restraints, using data for the site as a guide in assessing the forces involved. However, earthquakes need not be considered acting concurrently with wind.”

Nowhere does the code say ignore earthquakes because the pipe is on a specific item…. So there you go you need to consider earthquake loads regardless of what the pipe is sitting on. Consider may be anything from a computer static or dynamic analysis or it could mean some hand calcs using span formulas or it could mean simply strapping the lines down at some regular interval, but the word consider is not the same as ignore.

Thanks for the support and validation John. More power to you and the committee.

Regards

Gimini55 let me remind you too and the other members about the use of verb, "shall" and "should". As John quoted,

“101.5.3 Earthquake. The effect of earthquakes, where applicable shall be ......".

Notice the verb "shall" to mean mandatory and if it could have been "should" it would rather just be a recommendation or an option.

regards,

good point Ed... as a matter of fact there is an effort to edit B31.3 to make sure the shoulds become shalls.... the edit task group work long and hard on such tasks....

And by the way Dr. Becht will be publishing a companion to B31.1 c/o the ASME press soon... I'm doing a review on it and it looks top notch!

Dr. Becht on B31.1...... for so long , my group has been talking about it just like what he did to B31.3 and here we go, I hope I can get a 10% discount with my membership. Let it go, let it go, let it go.

Regards,

If you have a free hand, not only should you be considering seismic as discussed above, but an isolated 30' platform is likely to cause some dynamic amplification. A while ago I modelled a vessel of about 8' dia on a 35'high skirt. It had a top platform with some large valves. When modelled from the ground up, the calc gave a natural frequency of about 2hz with and amplified peak acceleration of well over 1 g even though the ZPA was only 0.2 g or thereabouts. This was the wrong answer. Somebody else modelled the vessel as a weightless rigid element and got the right answer. Best policy is to go with the flow.