Dear Mr. Stone,
Your suggestion brings us back to the most debatable issue in any engineering analysis. How to decouple two interconnected systems. Let me tell you frankly. In my opinion, a comprehensive dynamic analysis of the piping system inclusive of the pipe supporting structure (like piperack) is not a feasible solution, both in terms of the effort involved in the modelling as well as the time taken for analysis. There is no such software, as far as my knowledge goes, that gives a comprehensive modelling options for all possible piping and structural elements.
So I suggest again that we do a comparative study of the Eigen frequencies of piping as compared to the structural eigen frequency. Based on the result we have several options:
a) Increase or decrease Eigen Frequency of the piping system b) Increase or decrease the Eigen frequency of the supporting structure. c) Use vibration dampers
In general, however, the structural members (specially of it is a concrete member) has a higher stifness than a piping system and the chances of a resonance is thus avoided.
Regards,
Pankaj Mandal
-----Original Message-----
From: Geoff Stone DD&D Australia [mailto:blenrayaust@yahoo.co.uk]
Sent: 29 May 2002 03:28
To: PipingDesign@yahoogroups.com
Cc: Sunny Cessna
Subject: RE: [PipingDesign] Query
Dear Mr Joshi,
May I preface this by saying that I am not a structural engineer.
In vibrating applications such as in a coal prpeparation plant (sometimes
referred to as a coal washery ) the vibrating screens cause vibrations for
the
structure. In my experienc ethe structural engineers were always concerned
about the natural frequency of the building in respect of the exciting
frqequency. they would go to great lengths to change beam sections in order
to
avoid this occurence.
There are of course other means of excitation such as earthquakes that
require
a pectrum analysis to determine if the excitation is in harmony with the
dynamic response.
I use Algor's pipepak for modal analysis of piping systems to establish the
response to excitation from positive displacement pumps. This package has a
FEA
component that allows the input of AISC sections as structures for pipe
supports. I doubt if it is comprehensive enough to cover a whole structure
as
in a building but you should check with Algor. They are very helpful and may
be
able to provide you with more information.
Geoff Stone
--- Mandal Pankaj <Pankaj.Mandal@siemens.com> wrote:
<HR>
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<tt>
Dear Mr. Joshi,<BR>
<BR>
Normally piping systems are more flexible than supporting systems (of
course<BR>
with exceptions). The reason behind this is that as a piping engineer, a<BR>
flexible piping system is always preferred whereas a structural engineer
is<BR>
interested in making the structure rigid by adding bracings etc.<BR>
<BR>
Eigen frequency of a piping systems is determined by the supporting of
the<BR>
piping system which in many cases are governed by stress analysis and
hence<BR>
controlling the stifness of the piping system by adding guides is not
always<BR>
possible. Of course, we can modify stifness of the piping system by
adding<BR>
snubbers but again the cost and utility of the same should be
investigated.<BR>
On similar lines, civil structures have also their own limitaions in the<BR>
range of eigen frequencies.<BR>
<BR>
In general, making one system more flexible than the other is often not<BR>
possible from engineering point of view. What you have to look for is
the<BR>
comparative study of the eigen frequencies of the piping and the
supporting<BR>
structure. You may refer to the FEMA302, 1997 code for a comparative
study.<BR>
<BR>
However, I am still unable to understand your last question.<BR>
<BR>
Regards,<BR>
Pankaj Mandal.<BR>
<BR>
-----Original Message-----<BR>
From: KAUSTUBH JOSHI [mailto:kvj@epc.ltindia.com]<BR>
Sent: 28 May 2002 17:07<BR>
To: PipingDesign@yahoogroups.com<BR>
Subject: [PipingDesign] Query<BR>
<BR>
<BR>
Hi all,<BR>
<BR>
When designing the piping and support structure, what is better:<BR>
1) To have a rigid piping and flexible support structure?<BR> 2) To have a flexible piping and rigid support structure?<BR> 3) To have a rigid piping and rigid support structure?<BR> 4) To have flexible piping and flexible support structure?<BR>
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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Wed May 29 01:16:00 2002
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