Normally we get response spectrum at ground level. If a pipe is running on pipe bridge which is at say 8 m , is there any code which calls for application of any amplification factor which has to be used for obtaining spectrum at pipe rack level ?
Do we need to multiply the ground spectrum with this factor and input new spectrum and apply the same for nodes corresponding to pipes at that level ?

Is there any method to amplify the spectrum as described ?

Regards,
bag_piper

Dear,

At each elevation you will find different response spectrum. In my current company, spectrums are calculated by civil, if we are going to perform a dynamic analysis.

For static equivalent calculations, displacements are imposed on each supports. This displacements depends on structure configuration and stiffness, so may be calculated as usual.

Regards.

Sir,

The project bid document says that "Seismic analysis shall be based on a linear dynamic analysis based on modal & spectral analysis. The applicable response spectrum are those applicable to their support anchor point locations. In addition to inertial effect, differential anchor motion shall be taken into account ."

Now our defense is that we can apply same spectrum for piping running on sleepers and on pipe rack of 8.0 m TOS ( same piping continues from sleepers to rack) since we are already superimposing the pipe rack structural deflections in response spectrum module and not static module. Pipe rack deflections are due to seismic event.
Now that we are applying pipe rack deflections at supports derived from pipe rack , why we need to additionally use different spectrum at 8.0 m ?

There is one more issue -
Since there are displacements superimposed , whether we can compare the induced stresses with displacement stress range , i.e. ( EXP) and not with OCC limits , i.e. 1.33 SH ? In dynamic module whether we need to make the stress check case as EXP ?
This is as per 319.2.1 (d) of 31/3 which says that-
"Thermal displacements , reaction displacements ,and externally imposed displacements all have equivalent effects on the piping system , and shall be considered together in determining the total displacement strains ( proportional deformations )in various parts of the piping system"

Regards,
bag_piper

If you are using response spectrum module, you don't have to add displacements but you have to make sure you are using correct spectrum at 8m height. If you have some idea of how the rack is going to be and the dead load of pipes, you can ask a structural analyst to calculate amplified spectrum for you.

Alternatively, I don't know if this is correct but you can model the rack in CAESAR-II structural modeller and connect pipe with it using CNode. You will not need to amplify the spectrum in this case. But this method is a little complicated and requires some knowledge of structural analysis.