Re: dynamic stress analysis .

From: <Christopher>
Date: Wed Dec 29 2004 - 15:11:00 EST

On Dec 29, 2004, at 2:01 AM, Suman.Banerjee@ril.com wrote:

> response spectra is required to find out the frequency of nodal point
> at
> different time and to analyse that this frequency should not be same
> with
> the natural frequency to avoid resonance.
I don't want to get into a lot of hairsplitting about all this, but we really should get it right. A response spectrum shows the maximum response of a single degree of freedom (SDOF) system to a particular excitation. It's a plot of the maximum response against the frequency of the system. Since a multi-degree of freedom system responds like a collection of SDOF systems you can use the spectrum to find the maximum response of a complex system as the combined response of all the modes. The spectrum tells you about relative response, it doesn't have anything to do with resonance.

> Generally in dynamic analysis the pipes are considered as in plastic
> state,so
> allowable stresses are higher than the allowable stress defined in
> codes in
> static condition.

This isn't true either. safety critical systems usually are not permitted to yield for the OBE since they must remain operational. Some systems may be permitted to yield somewhat, provided they remain functional.

Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=fA__TAjtwbvmGBEQhts3-aeqKof9daf5vgwgnixR9LhH-SoWnWjn0qcEmOAZBvbS4ukjiije888M">chrisw@skypoint.com</a> | this distance" (last words of Gen.

...................................| John Sedgwick, Spotsylvania 1864)

<a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a> Received on Wed Dec 29 15:11:00 2004