Piping seismic analysis, structures influence 1

[carletes]

Dear all!

Regarding dynamic analysis of piping systems with earthquake forces, I see that most structural codes give ground acceleration and response spectrum at ground level depending on the location, but, if I am not wrong, piping system is subjected to the acceleration and movements of its supports, some of wich are attached to structures, and therefore I suppose that the response spectrum of the groung must be "corrected" in some way. Is it so? Is there any code, publication, guide etc that helps in getting such reponse spectrum of the piping supports without carrying out and exhaustive dynamic analysis of the structures?

Any help will be really appreciated.

best regards

 

[BRIS]

I last looked at this problem some 15 ears ago - and investigated a number of papers from the nuclear industry. I regret that I did not keep the references.

My conclusion was that since the whole pipeline and its associated structures are buried then they move together with the ground and there is no need to consider seismic forces.

I have been neglecting seismic acceleration ever since - but I may be wrong and I would be interested in seeing answers from those better qualified in this field.

Brian

 

[carletes]

Dear Bris,

Perhaps I did not explain myself very well but the pipes I am thinking of are not buried, they are aerial, so structures do not move together with the ground.

best regards

 

[carletes]

Going on with my search, I have found that BSSC (

http://www.bssconline.org)

in "2003 NEHRP Provisions" states some rules for piping analysis under earthquake. Does anybody know if it is applicable for power piping? Moreover, it clasiffies the types of calculations to perform depending on the importance of the pipen its NPS and location. any comment?

Best regards

 

[BRIS]

Dear carlets - my mistake - your question is perfectly clear
cheers Brian

 

[LSThill]

carletes (Chemical) & Team Members

Seismic Design and Retrofit of Piping Systems
July 2002

http://www.americanlifelinesalliance.org/pdf/Seismic_Design_and_Retrofit_of_Piping_Systems.pdf

Guideline for the Design of Buried Steel Pipe - July 2001

This guideline presents design provisions to evaluate the integrity of Buried steel pipe for a range of applied loads. It applies to new or existing buried pipe made of carbon or alloy steel; welded pipe; piping designed, fabricated, inspected and tested in accordance with an ASME B31 pressure piping code; and buried pipe and its interface with buildings and equipment.
Seismic Fragility Formulations for Water Systems (2 parts) - April 2001

This state-of-the-art study provides comprehensive data on damage to water conveyance systems caused by earthquakes around the world. The results represent an important element in the process of seismic mitigation of lifelines risks. Use of these fragility data will allow water system owners to estimate the vulnerability of their systems and make informed decisions to mitigate risks.

Seismic Fragility Formulations for Water Systems:
Part 1 - Guideline (104 pages)


Seismic Fragility Formulations for Water Systems:
Part 2 - Appendices (239 pages)


Leonard@thill.biz

http://www.thill.biz

 

[xhpipe]

Well you have one of two options...

Option1:
Gather data from the structural engineering folks. They may have captured what you need from their frame analysis... if they did a dynamic analysis spectra and G values may be available from their work.

Option2:
Create a model of the piping system, the structural frame and account for all large mass items such as equipment etc.. Then after you have a complete model together accelerate your model at grade. The partcicpation of the piping system and the "G" value increase due to the building frame interaction should be accounted for.

And yes you are correct in your assumption that the whipping action of the building may be signifiacnt in increasing the "G" loads the system will experience.

Finally don't forget SAM, Seismic Anchor Motion causes more failures than inertia. If you are unfamiliar with this I suggest you get some help from an experienced person in the field because you are navigating terra incognito.



Regards,
XHPIPE

 

[MJCronin]

carletes,

This book, (its out of print now) by Paul Smith, discusses seismic "response spectra" analysis of piping systems

"Piping and Pipe Support Systems: Design and Engineering
by Paul R. Smith, Thomas J. Van Laan

You may find old copies on the internet....

Additionally, the USNRC published guidelines on methods for response spectra envelopes (ie piping running between buildings) and SAM back in the heyday of nuclear power plant design (19805-1990)

Also, contact COADE ( the company that offers CAESAR-II, piping analysis software)

Good Luck !!

MJC

 

[vpl]

carletes

I think the short answer to your question is "it depends." And what it depends on are the postulated amount of seismic activity in the area and the stringency of the application (for example piping in a nuclear power plant is generally held to a higher standard than domestic water supply piping.)

If you go to the NRC website (

http://www.nrc.gov)

you can find references to the regulatory guides which MJCronin referenced. Specifically, you may like to look at Reg Guide 1.124, "Service Limits and Loading Combinations for Class 1 Linear Type Component Supports." You can access this document by following this link:

http://www.nrc.gov/reading-rm/adams.html

and typing "ML003739380" in the search box. [Note: If you are outside the United States, I can't guarantee the links will work.] This reg guide references the ASME Code, Section III, Article NF-1213, which would be another good source to review.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[frankandrews]

Carletes,

Current building codes take into consideration the height within the building in which equipment and piping are supported. If you have a FAX number, I can FAX you a couple pages which have the equations.


Regards,


Frank Andrews
SVS-Engineering
FAndrews@SVS-Engineering.com

Frank Andrews, PE
SVS-Engineering

 

[MikeHydroPhys]

Pipeline anchored above ground will flex according to the suspension characteristics (bridge design) and the fluctuations set up in the fluid due to the quake shock, plus compression along the line and shear from the distortion, this would happen tosome extent to pipe in the ground, plus the effect of lateral stress from shock wave disturbance of the soils. The problemof course with any point, or discrete load bearing system is the differential force on links and open span and it is these shear zones that should be given earthquake shock force attention and the span flex attention alike bridges with heavy dead load and some twist effect due to the contained fluid. There must be a mass of Alaskan oil data on this and plenty of bridge engineering column and tube (cable cladding) analyses and you may just end up with a highly conservative load bearing result to keep it moderately stable.
MikeHydroPhys

mdshydroplane

 

[ruth44]

For the seismic load of piping supported in a building one needs a floor response spectrum for the higher elevations within the building. The floor response spectrum is derived from the ground response spectrum, the soil properties and the dynamic properties of the building. This usually requires a dynamic computer analysis. The soil and building can magnify or damp the ground accelerations in certain frequency ranges of the ground response spectrum.The horizontal accelerations usually increase substantially higher in the building. The vertical accelerations usually do not increase so much at the higher floors. Piping that is supported well, also in the horizontal direction, can take very seismic loads. The thinking now is that the failure mode for well supported piping is fatigue.

 

[carletes]

Thank you all for your answers.

So, a dynamic analysis of the structures that support the pipes with computer is the only way to perform this type of designs? Isn't there any recommendation or publication for doing a "simplified" calculation? For example, to take the ground response spectrum and, depending of the heigth and type of structure, to magnify or damp such spectrum, without using computer progrmas??

Finally, calculating power piping according to 31.1, don't you consider that computing seismic stresses in the pipe and comparing them with 1.2Sh (as occasional load) is too conservative?

Best regards

 

[ashu1]

If you are looking for the static equivalent method for seismic analysis then ASCE 7 gives some guidelines for calculating "g" for piping systems which can be imparted on the piping system as a uniform horizontal acceleration. and yes it depend on the height of the structure.

cheers

ashu

 

[DavidCR]

For a simplified static seismic modelling for aboveground pipes. Som comments:

-Get a correct static force equivalent. Be sure you are using a correct lateral and vertical "g" force equivalent from your strucutral engineer. There is another aproach, calculating an equivalent force for which IBC or other codes state some rules and formulas.
Most of the cases the vertical seismic force is not considered.

-Most static analysis software lets you analyse with the obtained static equivalent applied uniformly to the pipe with the correspondent ocassional load factor and load combination depending on your criteria or code you are following.

-Be sure your pipe has a good natural frecuency and perform a good simple modal analysis to be sure your pipe is ok coorectly supported in this simple terms.

Remember that industrial facility damage on pipes is due to:
-Ground shaking (inertial damage),
-Relative displacemnet (anchor motion),
-Interactions (falling and swing impact),
-Soil liquefaction,
-Permanent ground movement,
-Landslides,
-Consecuential damage (fire, explosions, etc.).

In the case your pipe is a good candidate for a equivalent static analysis, remember that you are cosidering a simplification of the first two points notted. So be very careful.

 

[bvi]

As stated by various folks aboe, simple equivalent static per the building codes with an adjustment for height, is a simple way to consider this. You are correct that the ASME B31.1 factor of 1.2 or ASME B31.3 factor of 1.3 for these occasional loads is extremely conservative. There is ongoing work to develop a more realistic criteria, but that is where the codes presently are. When thinking about structural movements, do not forget differential structural movements which can tear the piping apart, when the piping is restrained by different structures moving in different directions.

 

[carletes]

Another question about seismic forces according to b31.1. According to section 104.8.2 of B31.1 "if calculation of moments due to earthquake is required, use only one half the aerthquake moment range". So, only one half of the reccommended static force due to earthquake must be considered? Is it so?

regards

 

[LSThill]

Hi carletes (Chemical) and Team Members

Please read the below technical paper:

http://www.bechtel.com/PDF/BIP/2003_4.pdf

Title: Seismic Analysis and Design with Maxwell Dampers
Authors: Mahendra P. Singh, F.ASCE, Dept. of Engineering Science and Mechanics,
Virginia Tech.
Navin. P. Verma, Engineer, Bechtel Power Corporation
Luis M. Moreschi, Engineer, Bechtel Power Corporation
Date: March, 2003
Publication/Venue: Journal of Engineering Mechanics
Copyright ASCE March 2003

Leonard@thill.biz

http://www.thill.biz

 

[stanier]

http://www.americanlifelinesalliance.org/pdf/Seismic_Design_and_Retrofit_of_Piping_Systems.pdf

You may also like to consider the paper at the above website.

 

[carletes]

Very good the link sent by Stanier (it appears to be some kind of draft used by ANSI B31, isn't it?). But I have an important question about it: why that document in section 4.3.2 take an amplification factor of 1 for any pipe? why the natural frecuency of the pipe is not considerated? taking an amplification factor of 1 would be valid only if the pipe was very rigid, but in the other cases? Is it conservative?

Best regards