Piping seismic analysis, structures influence
Piping seismic analysis, structures influence
(OP)
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
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





RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
Best regards
RE: Piping seismic analysis, structures influence
cheers Brian
RE: Piping seismic analysis, structures influence
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
www.thill.biz
RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
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 (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.
RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
MikeHydroPhys
mdshydroplane
RE: Piping seismic analysis, structures influence
RE: Piping seismic analysis, structures influence
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
RE: Piping seismic analysis, structures influence
cheers
ashu
RE: Piping seismic analysis, structures influence
-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.
RE: Piping seismic analysis, structures influence
RE: Piping seismic analysis, structures influence
regards
RE: Piping seismic analysis, structures influence
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
www.thill.biz
RE: Piping seismic analysis, structures influence
You may also like to consider the paper at the above website.
RE: Piping seismic analysis, structures influence
Best regards
RE: Piping seismic analysis, structures influence
You have come across a paradox that invariably gets ignored by most engineers; more often due to the difficulties in interfacing and establishing the actual seismic effects.
Referenced within threads are "magic" factors taken from ASCE 7, UBC or alike. When using such factors one must bear in mind that they are based on the primary structural system yielding/behaving in a ductile fashion. If the performance criteria of your "pipe" is such that it must remain elastic then you are goosed - since the raft displacements will govern the design of the pipe.
If you are designing to B31.3 (say) the earthquake is linked directly to UBC, and UBC gives little or no guidance. You then end up with ASCE 7(ish) and you could ferret out a factor, which for the reasons above is rather suspect.
The key to the whole deal is what is acceptable to the Client and Authority having Jurisdiction. One should also bear in mind the "custom and practice" in your respective industry may dictate alternate routes.
You have probably realised that the more you know the worse it gets... I advise to stop reading!!!
Invariably pipes perform well under earthquakes, the rather modest stress limitations in 31.3(3) do not consider plastic hinge formation and all that good stuff; normally the residual capacity is significant.
So in terms of what you need to do....
Be cautious about transitions in rafts, in this respect say from the ground to a piled structure; build in loads of flexibility. So that any settlement etc can be accomodated.
In terms of designing the systems.
1. Establish the performance criteria for the system; you may have 2 earthquake levels to design for typically 1 in 500yrs and say 1 in 5000yrs. In this respect the systems normally remain linear elastic under the lower event and you must ensure they do so!!!
If you have a single earthquake then ductility is the key and you will end up with significant attenuation of motion.
2. Establish with the Client etc what is acceptable; my experience is that normally response spectra or static G will suffice.
3. Failing this you may need to use Multiple Response Spectra, some form of enveloping or Time History.
You would be best shooting for the "quick and dirty method" of input spectra; if necessary make allowances in terms of seismic displacements between structures etc.
There is as you are aware an absence of data in the industry in respect of piping design!!!
The references you will find are rather contrdictory and embroiled in folklore and legend.
Good Luck
Lucifer